PDA

View Full Version : How White the Whites???



Arthur Morris
03-22-2008, 07:24 PM
This thread started in Avian Wild & Free but I have copied most of it here as it turned into a tremendous learning opportunity for me.

later and love to all, artie

While leading my IPTs I go to great lengths to ensure folks wonderful opportunities. On the recently concluded SW FLA Spring IPT, the last ever large (14 folks) group, we carried a bucket and a cast net out to Estero Lagoon on our afternoon trek. I was able to catch a variety of small fish that the Snowy Egrets enjoyed. Then I caught a mullet about 8 inches long. The snowies investigated but decided that it was too big for them. Out of nowhere a gorgeous Great Egret in full breeding plumage flew in and gobbled down the mullet before any of us knew what had happened... Fortunately, it stuck around and posed and posed for the group.

Canon 500mm f/4L IS lens with the EOS-1D MIII. ISO 200. Evaluative metering +2/3 stop: 1/1250 at f/4.

Don't be shy: all comments welcome. Later and love and thanks to Alfred and Fabs and Axel for their help on the IPT

Axel Hildebrandt
03-22-2008, 08:12 PM
Great-looking specimen, details, and BG. It could go a tad brighter for my taste.

Robert O'Toole
03-22-2008, 08:41 PM
This is what the image looks like with an embedded BPN monitor Cal strip. the whites are too dark, really they are a light gray. This was post was requested by Artie after I brought the dark image tone to Artie's attention. FYI the last square on the strip is not to reference a white tone in an image, the level is 255 so if any white in your image matches that tone it is totally blown :)
Robert

Robert O'Toole
03-22-2008, 08:43 PM
This is a repost with a more natural white tone and lightened (masked) BG.

Looks better to me, comments welcome.

Reposted with Vignetting correction of +23, +34 in CS3.

Robert

Linda Robbins
03-22-2008, 09:08 PM
Great repost of Artie's beautiful image. That is one gorgeous great egret!

Steve Wheeler
03-22-2008, 10:20 PM
Two thumbs up for the re-post!

Steve

Bob Blanchard
03-22-2008, 11:09 PM
That sure was a beautiful bird! Great work on the re-post Robert. Thanks Artie for a wonderful IPT, that was full of opportunities like this one. I love the ones I got of him too.

Leroy Laverman
03-23-2008, 01:50 AM
The repost is a nice improvement but it looks a little washed out with the lighter background. How about this version? Levels/curves adjustments with some selective sharpening on the bird's shoulder/neck through an edge mask.

The image itself has a nice painterly feel to it. The subtle color changes in the background are especially nice.

Arthur Morris
03-23-2008, 05:51 AM
Thanks to Robert and Leroy. Below is my re-post incorporating changes suggested by each. I have been in a "too-dark whites" rut lately. Thanks to all for opening my eyes to that.

I do prefer the background a bit darker than in Robert's version. The brightest whites are now R; 252, G; 240, B: 226.

The major question now is, "Is there detail in the whitest feathers?"

In an e-mail Robert, wondering about the vignetting, asked if the image was made with the 1Ds MIII where the vignetting would be expected. I double-checked: it was created with the 1DIII.

later and love to all, artie

Axel Hildebrandt
03-23-2008, 06:46 AM
I like Artie's repost best since the plumage doesn't have a blueish cast anymore and there is plenty of details.

Dave Phillips
03-23-2008, 06:54 AM
looks really nice now to my eye Artie, still seeing details in the whites.
Only found one teeny tiny wee itsy bitsy area in red channel at 255(guess that is on my monitor).....I was laughing and going nuts trying to find after looking at histogram, was a challenge. Definitely the dark bg looks good IMO. This has been a bit of learning experience

Arthur Morris
03-23-2008, 07:41 AM
Here is an e-mail exchange with Robert O'Toole that many might find educational:

ROT: 255 is pure white, with no detail. Since RGB is additive that means there is zero info there.


AM: Can you explain that. I understand that 255 is pure white = no detail but am confused about the additive part...

ROT: With RGB all the colors add up to make white. With LAB, there is a separate Luminosity, or black-gray-white tone channel. The color info separate. In CMYK is subtractive so no color at all, 0,0,0,0 is pure white.

AM: Should the whites be at 254?

ROT: Not usually. Best would be if they are one square over to the left of the whitest (255) box on the monitor calibration strip, that is, the tone next to pure white. Or, whenever there is detail in the whites.

You can, however, have the whites in the 230-240 range and not have any detail.

AM: That is what always bugs me; is there a way to explain that?

ROT: Yes, sometimes a white area on a bird looks blown, but when you measure the RGB value it is 241,245,242. The whites are not at all technically blown (overexposed) but the white lacks detail.

This has a lot to do with the surface and texture of an object. The softer and flatter the lighit technically is light-light-light gray and not pure white.

AM: That makes sense but I sometimes have whites in the sun, even in nice light, where the whites are at 245 but seem to lack detail... Is there an explanation for that?

Thanks for your help here Roberto!

And later and love, artie

Lyall Bouchard
03-23-2008, 09:10 AM
This thread is one of the best I've read on BPN. Thanks, Artie, for showing us that everyone can benefit from the knowledge here. And Robert, I ordered your APTATs CD a couple of days ago, and now I'm more anxious than ever to get it!

Robert O'Toole
03-23-2008, 11:27 AM
Here is an e-mail exchange with Robert O'Toole that many might find educational:


This has a lot to do with the surface and texture of an object. The softer and flatter the lighit technically is light-light-light gray and not pure white.

AM: That makes sense but I sometimes have whites in the sun, even in nice light, where the whites are at 245 but seem to lack detail... Is there an explanation for that?



I think in many cases it can be the quality of the light, diffused or direct, and the angle of the light, straight on and flat or angled to accentuate texture and details.
Also the camera itself can be a big factor (in terms or dynamic range), and the between the same cameras the settings can have a big impact (contrast and color space).
The RAW convertor used can have a huge impact. Breezebrowsers is much easier to use and faster in many cases but I dont like the way it handles white tones. I have found ACR (Photoshop's Raw Convertor) handles whites much much better with great detail in the whites.


Robert

Leroy Laverman
03-23-2008, 01:31 PM
Great edit Artie. One of the problems with bright whites (and dark grays for that matter) is that it becomes difficult for our eyes to see subtle differences between shades that are similar in the extreme ends of the color gamut. In the squares above the upper left square is (255,255,255) and the right is (245,245,245). It's easy to see the difference between them with a straight edge. In the bottom rectangle the white forms a gradient from over the same color range. Each block is shown against a dark and light background. In a high contrast scene our eyes have more trouble with fine shade differences. If you look closely you should be able to see vertical bands of gray in the lower rectangle (posterization effect). To my eyes its easier to see the shade differences with a light background (lower dynamic range) than with the dark background.

This optical effect shows up in editing images as well. For example the background colors in lightroom are fairly dark. If you get the image looking good then post it against a bright white background it will look too dark, even though it looked fine with a dark background.

Arthur Morris
03-23-2008, 02:03 PM
Hi Leroy, I am a bit confused. Can you please clarify the diagram above?

Thanks and later and love, artie

Leroy Laverman
03-23-2008, 03:01 PM
Maybe this is easier to see. The various color blocks are marked. On my monitor I can see vertical bands in the gradient region. You can see this numerically in photoshop if you scroll your pointer through the gradient region. If you can't see where the bands are then open the image in photoshop and move the midpoint slider towards the right in the levels menu.

I can see the bands fairly easily with the light background but it's harder for me to see against the dark background.

I hope that helps explain things better. It's complicated by the fact that all of our monitors or not the same - even when calibrated.

Dave Phillips
03-23-2008, 03:05 PM
this has been excellent Leroy....thanks for your time.
And thanks to you too Artie

Fabs Forns
03-23-2008, 05:54 PM
Excellent thread. Thanks to all involved!

Dieter Schaefer
03-24-2008, 05:03 AM
Leroy's demonstration is a very good one - our eyes are easily fooled. It also shows a problem with the concept of whites - as Robert alludes to: we consider 255, 255, 255 as "blown" and don't want the "whites" to reach that value - actually none of the RGB values should be 255. Trouble is - there are no "whites" - on the additive RGB scale there is only ONE white = 255, 255, 255. If you change the value to 254, 254, 254 you technically have gray - a very very light gray though. As long as you keep all the value identical, you will always have gray - exactly up to the point 0,0,0 which is black. So if your subject (egret) really is white you as a photographer would exclude his correct color from your consideration but not allowing it to be "white".

Again, technically speaking - change only one of the RGB values away from 255, 255, 255 - so 254, 255, 255, or 255, 254, 255, or 255, 255, 254 - then you are not talking white anymore but very light green, violet, or brown, respectively. This, of course, is a totally technical exercise - as Leroy pointed out, our eyes can not easily distinguish those small differences but will perceive a whole range of values as "whites" though they technically are light color "casts".

All the above does not even account for "white balance" - unless your light is exactly of one color temperature - let's say 5500K - any deviation from it will technically also register as "color cast".

This technical discussion is moot, however. As photographers, we are talking about detail or lack thereof - an area that is within a certain range of RGB values looks uniform to the eye - and we call this lacking detail. Whether or not this is because the subject really has no detail in that area or whether we already exposed the image incorrectly and "blew" it (the highlights that is).

We all know that to expose a mostly "white" subject correctly, we need to use some positive exposure compensation (Editor's note to avoid confusion: this is always true when you are spot metering but only sometimes true when using Evaluative or Matrix metering... Be careful here...) - and the reason for that is that your camera's exposure meter is calibrated for some "medium" gray, i.e. it assumes that your subject is reflecting somewhere between 12 and 18% of the light that hits it - without that exposure compensation, the egret would look very much gray. (Editor's note again: the situation is much more complex than Dieter is making it--he is here again referring only to spot metering. I would recommend that everyone check out my e-Zine article on Exposure as well as my additional comments in this Forum.)

If the egret was pure white - then we would have 100% reflection and hence a value of 255, 255, 255.

At this point, it is up to the photographer's experience to choose an exposure that attempts to match the percentage of light reflected from the subject - which could be measured correctly with an incident light meter (and in this day and age of digital cameras also get the "white" balance right) . Trouble is, for this to function properly, one would need to point the meter in the direction of the camera at the exact position of the subject - so hand that meter to the egret or make sure the egret doesn't mind that you get very very close to it.

(While Dieter is raising many excellent points here he is treading in dangerous waters; if you took a good incident meter reading while photographing a brilliant white bird you would need to stop down one full stop to maintain detail in the whites. This is John Shaw's Sunny f/22 for Whites....

The histogram is of great help here - but there are problems there as well. First off, it works of an 8-bit JPEG with all your camera settings applied - but you are shooting 12-bit or even 14-bit RAW (where white is either 4096, 4096, 4096 or 16384, 16384, 16384, respectively). So what we really try to achieve is not to have our exposure chosen in a way that the values "bunch up" against the right side of the histogram - which unless the subject reflects that much light would be interpreted as an overexposure = blown out highlights.

To sum this up, there is nothing inherently wrong with a value of 255, 255, 255 in your image - IF you are certain that there is an area in the subject that reflects all the light that hits it. Under those circumstances, there would be nothing wrong with the values "bunching up" on the right side of the histogram either. In practice though, it is "safer", to avoid that scenario, as it will - correct or not - generally be interpreted as an overexposure.

As Leroy pointed out - the eye has trouble distinguishing those fine changes in the "whites" and as Robert pointed out - detail or lack thereof has much more to do with quality of light and the light incident angle on the subject.

Arthur Morris
03-24-2008, 08:52 AM
Thanks Dieter for your many excellent comments above. I did add some editor's notes on exposure to your post as your were treading dangerously with your exposure advice. I do not think that we run into too many birds that are pure white...

Later and love, artie

Leroy Laverman
03-24-2008, 10:08 AM
The only things in an image that I don't mind being blown out (255,255,255) are strong specular reflections. The catchlight in eyes is a good example. A direct reflection of the sun (or flash) should probably be way overexposed to avoid way underexposing everything else. We have to make compromises somewhere. A real world scene may have 15 stops of exposure to cover 'correctly' while our film/transparency/sensor can only cover 8-11 or so. We have to judge how to compress this information into the available dynamic range.

For those that want to see all this in a technical manner this link explains things fairly well (http://www.normankoren.com/digital_tonality.html). I'm a chemist by trade so the technical aspects are fascinating to me. I also think it helps to understand what our cameras are doing with the light that comes through the lens. Noise is a big issue that is talked about frequently, especially in shadows. As a scientist this is simply a signal to noise ratio (S/N) problem. The thing to do is to overexpose by one or two stops with a raw capture then pull the exposure back to 'correct' after. The noise levels for a given sensor/ISO combination are fairly constant so by over exposing you've increased the signal and the apparent noise is less. The idea of "expose to the right" as talked about on the Luminous Landscapes site is based on this.

Wayne Nicholas
03-24-2008, 12:52 PM
Excellent post all the way around. Tons of useful information in this. Thanks.

Fero
03-24-2008, 01:16 PM
There are a few more issues - calibration and quality of the display itself. On my poor LG I hardly see anythiong above 245 :-( so I rely purely on measuring RGB. Often I must make compromises and say myself "sometimes white is white" and keep it ?blown.

Dan O'Leary
03-24-2008, 01:33 PM
One other thing to consider amongst all this great info - this is one more reason to use 16bit until the final output. Disk space is cheap and computers are fast. Getting 15bits of color data per channel (2^15 = 32768 "steps" rather than 2^8 = 256) is priceless when dealing with challenging exposures like Artie's fabulous photo.

Patty Sullivan
03-24-2008, 01:39 PM
Absolutely gorgeous Egret. Wow. I am reading the tips here.

Asher Kelman
03-24-2008, 01:43 PM
White 255,255,255, is not necessarily blown. It is just the whitest-white beyond which not whiter white can be demonstrated. If however, we had lights for each pixel, the flux could be dialed in to higher levels, which would just burn our eyes. So it's an issue of the scale being stopped at 255,255,255 such that is perceived at white-white in a modestly illuminated room.

The critical thing about shooting white is a collection of rules and ideas we mostly already know but do not always integrate when thrilled by the site of a wonderful bird in flight.


Cameras all have bias, like looking through a very slightly tinted window: The camera should have been already profiled and then we can remove the fingerprints of the camera on whites and one can record the birds colors as seen and colors of sunsets maintained! If we want to remove the cast of foliage reflected light (or even of sunsets), a gray card reference shot is used.


Light cannot overwhelm the shot, that's obvious! Use higher speed and neutral density filters if needed. In almost all circumstances, one can reduce aperture and increase speed. For the very best structural detail in the whites, however, if you can, avoid restrictive apertures tinier than f8 or 11 with a 1DIII or one is marching into degradation of the detail (as the light waves get overlapped) by the diffraction, smoothing out micro detail!


A modest illumination is best, so that the different reflectivities of the feathers of each part of the plumes can be defined, one micro detail against another. So for this, a slight under exposure may be best. Otherwise, the resolving power of the lens has nothing to cut into different pieces. All the pieces record close to the same.


Next, the direction of the light should be from the side to create micro shadows and bring out detail in three dimensional forms that may actually have identical reflectivity of 250,250,250! If not for some directivity of the light, the dimensional information in areas of unifform reflectivity would be lost. This is part of the reason for photographing early or late in the day, but of course you all know that already!




I hope this is of some value to a few to put this together.

Asher

Patty Sullivan
03-24-2008, 02:21 PM
Great help! Thankyou! Now if I had only studied more I would understand all the lingo! lol. http://zazzle.com/farmer77

Johnny Bravo
03-24-2008, 03:50 PM
Great thread. Let me recap what I've learned:

'Avoid shooting white birds. It is much, much too complicated for me'.

I'm sticking to LBJ's (little brown jobs) from here on out!!!

(But seriously folks--great thread--that image in the final iteration is just fabulous!)

Best to ya,
John

Jim Poor
03-24-2008, 04:35 PM
Wow great info here. One thing to add is that when we start talking about prints, the numbers change once again. Paper white is usually around 247 so anything higher than that will result in no ink and therefore no detail.

Roger Clark
03-24-2008, 08:58 PM
Another factor not discussed in this thread so for is that of visual perception, which is quite complex. For example, in bright office light, small details around 1-arc-minute in apparent size need on the order of 20% contrast to be just discernible wheres at about 20 arc-minutes in apparent size one can detect around 0.5% contrast details. The contrast detection drops (you need higher contrast) as light levels drop. So if you want to show detail in the highlights, you need to stretch the contrast for the target illumination.

Reference:
Blackwell, R.H., Contrast Thresholds of the Human Eye, Journal of the Optical Society of America, v36, p624-643, 1946.

Roger
http://www.clarkvision.com

Arthur Morris
03-25-2008, 04:31 AM
Another factor not discussed in this thread so for is that of visual perception, which is quite complex. For example, in bright office light, small details around 1-arc-minute in apparent size need on the order of 20% contrast to be just discernible wheres at about 20 arc-minutes in apparent size one can detect around 0.5% contrast details. The contrast detection drops (you need higher contrast) as light levels drop. So if you want to show detail in the highlights, you need to stretch the contrast for the target illumination. Reference: Blackwell, R.H., Contrast Thresholds of the Human Eye, Journal of the Optical Society of America, v36, p624-643, 1946. Roger

Hi Roger, Can you translate that for us? It appears in the fist part that you are saying the it is easier to see contrast when viewing an image in bright light than in soft light. Is this correct? (I would have thought that it would have been the opposite...)

You wrote: "So if you want to show detail in the highlights, you need to stretch the contrast for the target illumination." What do you meant by stretch the contrast and what is the target illumination? (Is the latter the light that you will be viewing the image in?)

Thanks and later and love, artie

ps (respectually) to all: While several of the highly technical comments here may be entirely accurate, the goal is to provide information so that the average Joe can make their images look better. I have never been accused of being at all knowledgeable as far as the techinical aspects of photography are concerned, but that has never stopped me from making good images.

alan321
03-25-2008, 07:03 AM
Keeping (capturing and showing) details in the whites is a lot like keeping the details in the reds of bright red flowers. The colour of interest has texture but the texture consists of subtle variations near the maximum displayable level on your screen or print, and if it is too subtle then you cannot distinguish it.

Assuming that we have captured the details in the first place we can show them better by reducing overall exposure. However, that ruins the overall impression of the subject and other tones. That's where this thread started - with a grey egret instead of a white egret.

The next best solution may be to apply curves or contrast adjustments so accentuate the apparent difference between those whites (or reds) that have been recorded up near the maximum showable level. This keeps the middle tones near the middle and the dark tones dark, but increases the differences in the bright tones enough to be readily visible. It can work well but be careful when doing this because if your monitor - calibrated and profiled or not - does not have sufficient colour gamut then you will not be seeing what someone with a better monitor or printer will see, and you may actually ruin your image. Laptop screens have a small colour gamut and are prone to causing this sort of over zealous editing.

A third method, a bit like the first, involves desaturating colours. It's not so good for white subjects as it is for reds or blues or greens but by discarding colour you may leave visible tonal details. Trouble is that the colours then look wrong. Also, it may not be needed if you have a monitor with adequate colour gamut. (that, by the way, is how I ended up with an Eizo CG monitor to use with my laptop).

Robert mentioned the sunny f/22 rule. I'll have to read up on it's applicability to modern digital photography but I'm not convinced that it is appropriate because it affects the capture of mid-tones by darkening them. If you have a good digital SLR with lots of dynamic range (such as a 1Ds2 or 1D3 that can capture over 9 stops of useful dynamic range) then you ought to be able to capture the whites and keep the midtones correct if you shoot raw format. Shooting jpegs is far too limiting to get the dynamic range that you need. Displaying those captured whites is quite separate from capturing them, as the display device or print probably has less dynamic range than the camera.

The bottom line, however, touched on in the post by Dieter, is that maybe we are not meant to see the details. If you look at an egret in sunlight how much fine detail do you actually see ? I'd suggest that unless he's dead or been captured and you take him into the shade and study him up close you'll see precious little other than "bright white". So then we have the photographer's dilemma: should we make the image realistic or should we enhance it to look detailed. With some subjects we just cannot have it both ways no matter how good our lens and camera are. I still struggle with this dilemma. Generally I prefer to see the details but if it can only be done by making the subject "look wrong" then I avoid it.

- Alan

Roger Clark
03-25-2008, 08:38 AM
Hi Roger, Can you translate that for us? It appears in the fist part that you are saying the it is easier to see contrast when viewing an image in bright light than in soft light. Is this correct? (I would have thought that it would have been the opposite...)

You wrote: "So if you want to show detail in the highlights, you need to stretch the contrast for the target illumination." What do you meant by stretch the contrast and what is the target illumination? (Is the latter the light that you will be viewing the image in?)

Thanks and later and love, artie

ps (respectually) to all: While several of the highly technical comments here may be entirely accurate, the goal is to provide information so that the average Joe can make their images look better. I have never been accused of being at all knowledgeable as far as the techinical aspects of photography are concerned, but that has never stopped me from making good images.

Hello Artie,

There are several implications for the effects of visual perception. You are correct: it is easier to see lower contrast details in bright light than dim light. But it also depends on the size of the subject. For example, further up this thread are test examples with large patches (e.g. the 255,255,255 versus 245,245,245 that have a contrast of (255-245)/245 = 4%. In good light that is easily discerned on a print or on screen. But that same 4% contrast difference would be difficult in dim light. But more important for the example of your egret is details in the feathers. Those details will appear a small fraction of a degree to our eyes when viewing the image. Those details if stretched to have 4% contrast would not likely be visible, and one would need to stretch the image further in order to bring the contrast to a level that can be discerned. (I haven't measured the contrast in some of the fine detail in the egret feathers, but I bet it is 10%, 20% and greater in some of the images posted.)

When I said stretch for the target illumination, I meant, for example, the light that the print would be viewed in, or the brightness of the monitor. A print displayed in a bright office environment needs different contrast than a print viewed in typically dimmer lighting in someone's living room.

There was some discussion that 254,254,254 is not white. But the contrast difference between 254 and 255 is so small, that even with large patches it would be difficult to distinguish between the two. So to our eye, 254 appears very white.

The bottom line, ignoring all the technical details of 255 versus 254 and contrast threshold of the human eye: stretch the details so that you can easily discern the details you want people to discern. Monitors are one thing (most people these days seem to be getting uncalibrated LCD monitors with too high a contrast) and are uncontrollable with regard to web viewing. But a print should be tested by viewing it in similar lighting where it will be displayed.

Another factor with digital capture and bringing out detail in the highlights: digital capture (in raw) is linear. The raw converter applies a variable gamma curve compressing the highlights. If you have trouble recovering details in the highlights, they are really there in the raw file (unless saturated), and a linear conversion (which many raw converters unfortunately do not have) will bring out the maximum detail in the highlights.

Roger

Pat Gautier
03-26-2008, 03:00 PM
I would like to echo and elaborate on Alan's response: While it is necessary and beneficial to understand the technology and how it works, the ultimate goal is to produce a visually pleasing image. I am not nearly as concerned with touching the right side of my histogram as I used to be for a number of reasons some of which have been touched on here but all of which are based on my experience in attempting to produce visually pleasing images. When we looked at the first image posted above, we made a subjective judgement about how it appeared to us. After finding it lacking in some quality, some elected to further analyze the root cause or correction. The analysis led us to an arguably much improved result, but that again is a subjective evaluation and not necessarily dependant on all numbers reaching a certain threshhold and no more. I have taken images of egrets where areas of the plumage had no apparent detail but it was appropriate for the lighting and location and created a visually pleasing result. I have also taken images of egrets in dense shade where pushing the whites to their absolute maximum would have created an unnatural appearance to my eye. In that situation the slightly gray egret was more visually appealing and nobody would have argued based on that photo that I had shot an image of a gray bird. (I do not profess to be a photographer of the caliber of many posting here but my website does have examples of the above) Know and understand the technology and how to manipulate it but do not be so constrained by the rules that you may distroy a visually appealing yet techically incorrect image. To beat the horse just a tad more, what we are really talking about is correcting exposure and I think we all know that the correct exposure is the one that gives the result you are trying to achieve.

Thanx for letting me join in the discussion,
Pat

Roger Clark
03-26-2008, 11:41 PM
Following on Pat's theme, how about this image? I have had numerous emails/(other) forum posters say the image is saturated and there is no detail in the brightest areas. Yet no pixels have a value of 255 (the posted image has a max of 242 (excluding the lettering). Are you able to see details in the brightest parts? I can see detail just find in the brightest areas on my calibrated monitor.

This image was about the fullest full moon one can get without an eclipse, and the bright portions appeared quite bright to my eye, and that is what I wanted to show in the image. Of course I could pull the brights down and add contrast, but that is not what it looked like to me. What do you think?

Photo details:
Canon 1D Mark II camera, a 500 mm f/4 L IS lens with a 2x TC and IS was on. The total focal length is 1000 mm for a full scale of 1.7 arc-seconds per pixel. The image is a single frame HAND HELD 1/500 second at f/9.1, ISO 200. Exposure was manual.
More details and the full resolution image is available here:
http://www.clarkvision.com/galleries/gallery.astrophoto-1/web/moon.rnclark.handheld.c10.25.2007.jz3f6583f-8s-800.html

Roger

Arthur Morris
03-27-2008, 01:24 PM
Hi Roger,

re:

Following on Pat's theme, how about this image? I have had numerous emails/(other) forum posters say the image is saturated and there is no detail in the brightest areas. Yet no pixels have a value of 255 (the posted image has a max of 242 (excluding the lettering). Are you able to see details in the brightest parts? I can see detail just fine in the brightest areas on my calibrated monitor.

AM: Same here; everything looks fine. And a nice image to boot. And sharp.

This image was about the fullest full moon one can get without an eclipse, and the bright portions appeared quite bright to my eye, and that is what I wanted to show in the image. Of course I could pull the brights down and add contrast, but that is not what it looked like to me. What do you think?

AM: Here is my problem. You wrote, "I could pull the whites down and add contrast." My understanding is that when you add contrast the whites get brighter so the above does not make sense to me.


Photo details:
Canon 1D Mark II camera, a 500 mm f/4 L IS lens with a 2x TC and IS was on. The total focal length is 1000 mm for a full scale of 1.7 arc-seconds per pixel. The image is a single frame HAND HELD 1/500 second at f/9.1, ISO 200. Exposure was manual.

AM: Nothing personal but why in the world would you not use a tripod when working at 26X magnification?????????????

Later and love, artie

ps: Please expain what a full scale of 1.7 arc-seconds per pixel means. I am pretty sure that less than 1% of the folks reading this (me included) have any clue as to what that means. As I stated previously, while it does not hurt to understand the technical stuff the idea is to help the average photographer make better images. If we (obviously) have no clue as to what arc seconds per pixel means, how can we learn anything?

Roger Clark
03-27-2008, 11:51 PM
Hello Artie,

AM: Here is my problem. You wrote, "I could pull the whites down and add contrast." My understanding is that when you add contrast the whites get brighter so the above does not make sense to me.

If I reduce the intensity of the whites, then when I boost the contrast, the brighter portions of the image will be increased back to a higher level so one can balance the decrease in brightness with the increase in contrast so the brightest pixels do not saturate. I bet you've done this many times and I'm probably not explaining my idea well enough. This can be done, for example, with curves, or with a selection and levels, and the photoshop shadow/highlight tool can do a nice job.

AM: Nothing personal but why in the world would you not use a tripod when working at 26X magnification?????????????

Yeah, normally I would use a tripod. I find the moon is a good test subject that can be repeated by anyone anywhere in the world. Sometimes I've found myself grabbing my 500 mm lens with no time to set up a tripod, so I'll quickly fire off a few frames before the bird/animal flees. Then if the situation is stable, I'll go ahead and set up the tripod/window mount/beanbag. So for the moon shot, I was testing my technique. It certainly was not easy to hold the 500 steady, especially with a 2X TC. But I proved to myself that I can take a sharp image when I must react fast.

AM: ps: Please explain what a full scale of 1.7 arc-seconds per pixel means.

Sorry, I should have explained it. But it does illustrate an interesting concept (well maybe for math geeks). If one wants to achieve maximum resolution on a subject, e.g. a distant bird, the angular resolution tells you what you'll get. For example, which gives more detail: on a distant bird: 1) a 1D Mark II with a 500 mm lens or 2) a 400 mm lens on a 40D? The answer has nothing to do with crop factor and everything to do with pixel spacing and focal length. To calculate the angular spacing between pixels use the following formula:

plate scale = 206265 * pixel_pitch / lens_focal_length, result in arc-seconds/pixel

The 206265 factor is the number of arc-seconds in one radian. Plate scale is an old astronomer term for what one got on photographic plates back in the days when glass plates were used.

1) 1D Mark II has 8.2 micron pixel spacing, so with a 500 mm lens, the angular resolution, or the plate scale is:
206265 * (8.2 microns / 1000 microns/mm) / 500 mm = 3.4 arc-seconds/pixel

2) 40D with 5.7 microns pixel spacing, 400 mm lens: plate scale is:
206265 * (5.7 microns / 1000 microns/mm) / 400 mm = 2.9 arc-seconds/pixel

So the 40D combination has smaller angular resolution and a bird would 17% more pixels taller in the 40D image.

(The 1D Mark II image would appear less noisy due to its larger pixels, however.)

As one approaches 1-arc-second, it is such a small angular size, that maintaining steady pointing becomes very difficult,
and if the subject is very far away, atmospheric turbulence can be an added blurring factor.

If the digital camera exif data includes range to the subject, then one could use the angular resolution and range to measure things in the image. For example, how long are the claws on an eagle? I've always wanted to measure the claw lengths on some of my Alaskan brown bear photos, but can't find the range data in the exif data for my 1D Mark II. People ask me how close I was to an animal when they see the photo. Any ideas if the range data is in the Canon exif data, and if so, where?
I've had people say it's there but not where. (I'm way of subject topic now.)

Roger

Alfred Forns
03-28-2008, 08:53 AM
Hi Roger I'm sure you are correct in all your are explaining I'm also sure you must know it si going over everyones head

This brings to mind the time I spent in doing fine art b&w photography It seem the only way to arrive at the right exposure had to be the most complicated and complex.

btw please send me a pm with your full name so I can make the update We would like all members having full names for user names Thanks

alan321
03-29-2008, 06:06 AM
This thread has developed beyond a discussion about exposure to include the topic of visible detail and resolution. Otherwise I would not post the following here. My intention is to make the concept easier to understand but if I have failed then perhaps you know why I'm not a teacher :)


When we look with our eyes we see an angle of view. The level of details that we can resolve depends on the level of contrast of those details and also on the angle of view they cover. This is a physiological characteristic of our eyes and brain. If the details cover a wide angle of view then we can hardly miss them. If they cover a small angle of view then they become harder to resolve.

The angle of view can be measured in various units much like temperature or distance can. Most of us know about degrees, minutes and seconds, in which a second is 1/60 of a minute and a minute is 1/60 of a degree. 360 degrees covers a full circle of view (fisheye). Another measure is gradians (400 grads to a circle) and another is radians (approximately 6.3 (2 x Pi) radians to a circle) but to keep it simple I'll stick with degrees.

There are a number of ways that we can use to increase the angle of view covered by each detail. e.g.:
1. we can get closer (but too close and we cannot focus, or the thing bites us on the nose or just flies away). As we get closer the angle of view that it covers gets bigger.
2. we can use a lens that magnifies the size of the details more than our eyes can (binoculars, telescope, etc.)
3. we can take a photo and enlarge it and look at that instead of the real thing (so long as the photo captured the necessary detail in the first place)

I've been using the term angle of view, but I could easily call it an angle of arc. If you imagine stright lines from the extreme sides of an object to your eye, then the angle betweeen those lines where they meet at your eye is the angle or view covered by that object. An arc-second defines an arc that covers an angle equal to 1 second, or (1/60) x (1/60) x 1 degree. An arc-minute covers (1/60) x 1 degree. We can see things that are bigger than about 0.3 arc-minutes or 18 arc-seconds. Roger was explaining that each pixel on the various cameras with long lenses sees a part of the image that can resolve the equivalent of an angle of view of about 3 arc seconds. That means that with a tele lens on the camera we can capture details that are one sixth of the smallest size that we can see with the naked eye. Yay. But if we had a shorter lens then each pixel may cover less detail than we can see with the naked eye. That's partly why wide angle shots never seem to capture the same level of detail that we saw - lots of items but each one is a bit small and so it becomes vague and undetailed. Even a standard lens on these cameras is struggling to do better than good eyes.

What Roger did not mention is that his camera / lens angle of view was only theoretical to the extent that it assumed a perfect lens. It was about lens angle of view rather than actual real-life lens resolution. A real lens has its own optical limitations that further reduce the amount of detail captured by the camera. The camera pixels still see the same angle of view through the lens but the view is somewhat clouded.

Of course it doesn't matter what the camera captured until we display it or print it. Until then it is invisible. So how much detail can we see in a print ?

It has been published somewhere (probably by Norman Koren in one of his highly detailed articles on scanning and resolution - I'll try to find a reference) that people with excellent eyesight can resolve printed details in good lighting as long as the details are big enough to cover at least 0.3 arc minutes or 5 thousandths of a degree. How big is that ? Well, it depends how far away those details are. At 10 inches it is about one thousandth of an inch. It would need a printer at about 1000 dots per inch to show it. [At 100 yards it is about 0.3 inches. Have you noticed how hard it is to see a fence wire at 100 yards, other than when the sun is glinting off it ? At 10 yards we are struggling to see 0.03 inches or 0.8mm. That's why we can't see all the fine detail of a feather at that distance.] Back to our print at 10 inches... We can see something that is bigger than 0.001 inches. If we put two of those somethings beside each other then they become a big something of 0.002 inches. We need a gap between them if we are to see them separately in a group or pattern, but the gap also has to be at least 0.001 inches or we won't see it either. So now our print resolution is down to about 0.002 inches. That means we can see a repeating pattern of maybe 500 lines per inch. If the source material happens to not line up with the printer dots then we can resolve less. Say 300 lines per inch. This is why 300 pixels per inch is about as good as most of us need when sending images to the printer. We let the printer use 1200 or whatever dots per inch so that it can use a pattern of dots to make up the required colour and tone for each image pixel, but the pixels that are smaller than 1/300 inches start getting too hard to separate and resolve consistently. Sometimes it works and sometimes it doesn't. 300 ppi is pretty reliable.

Now we can get to the other factor touched on previously. As well as physical size we need optical contrast in order to separate and resolve the details. Two adjacent dots with almost identical colour and tone are effectively one big dot. We cannot tell them apart. Our bright white egret feathers are represented in our photos by a bunch of almost identical pixels. We are limited in how much we can enlarge the detail by the resolution of the photo. Too much enlargement adds no new info and doesn't help. To see the details in a smaller print or on screen we need to exaggerate the contrast between adjacent pixels that are very similar in colour and tone. We can use curves in photoshop to do this. One of those "S" curves that enhance contrat at the bright end of the scale but reduces it at the middle tones. Alternatively we apply lots of sharpening until we start to see halos but that looks rather too unnatural.

Mention has been made of using a maximum value of 254 instead of 255 for whites. By using something less than 255 we are sure to get at least some ink on the page. That might prevent those horrible bare patches where the glossiness of the page and the glossiness of the ink are so different that we can immediately tell where there no ink at all. As long as some ink is there the glossiness is consistent over the whole page.

I hope this has clarified some of the concepts for some of the readers but the fact is that many switch off as soon as they see numbers. That's partly why most photographers are point and shooters. No disrespect intended or needed, it's simply the way of the world. If you can understand the concepts then you'll be better for it than someone who does what they're told without knowing why. That's what learning is all about.

- Alan

Arthur Morris
03-29-2008, 06:36 AM
Dear All, While I am sure that there are some who appreciate the technical discussions and actually follow and understand them, I must reiterate: I do not know anything about arc minutes or arc-seconds per pixel. Heck, I do not even have a good understanding of resolution (in its varying forms). Yet, over the past 25 years I have managed to make a few good images. Alan, as one who is turned off by the technical discussions above does that make me a point and shooter???

later and love, artie

alan321
03-29-2008, 08:13 AM
No Artie, you've risen above that but despite all of your hard-won skill and talent you still posted a shot of a grey egret with little apparent feather detail. Collectively we were trying to teach readers how to avoid that and furthermore how to capture and extract subtle fine detail from an image and even let people realise why it isn't even possible with some gear in some situations.

You've been a teacher. Is there any point trying to teach high school stuff to primary schoolers ? It can be done but it usually takes a few years. Most school students do not want to go to university. Good for them. There's a place for everyone and their preferance certainly does not necesarily reflect their intelligence or ability but it also certainly will impact how and what they learn in future. Likewise, many photographers will not understand technical aspects of photography and even if they want to it will take a lot of pregressive training or teaching to achieve it. I'm sure that some of your readers are part way there already and can handle some technical info.

We've somehow gotten into some technical stuff here and the only signal we're getting is go away and keep it simple enough for everyone to understand it. I tried to simplify it but apparently not enough. If you want to keep all photographic discussions in the educational resources forum to a non-technical level at the lowest common denominator then that's fine but it will hardly enlighten those who might be interested and willing to pick up on technical or complex aspects.

I apologise if I sound a bit short but I was only trying to help, as were the others. We know that what we write is not for everyone but that doesn't mean it is fit for no-one. I'll steer clear of offering such input in future but unfortunately that limits what I can offer because I don't have your level of practical experience to draw on. I guess I'll be a lurker :)

Cheers all,
- Alan

Arthur Morris
03-29-2008, 08:44 AM
Hi Alan, re:

No Artie, you've risen above that

AM: That being my lack of technical knowledge?

but despite all of your hard-won skill and talent you still posted a shot of a grey egret with little apparent feather detail.

AM: As I stated stated previously, I had been in a "My Whites are too Light" funk and am glad that Robert O'Toole and others helped me get out of that funk. Understanding the technical aspects did not help me get out of that funk. I still do not have a clue as to what an arc-seconds per pixel is but my pix are looking better.

Collectively we were trying to teach readers how to avoid that and furthermore how to capture and extract subtle fine detail from an image and even let people realise why it isn't even possible with some gear in some situations.

AM: Agreed.

You've been a teacher. Is there any point trying to teach high school stuff to primary schoolers ?

AM: No, but that is exaclty what the technically minded folks are trying to do here.

It can be done but it usually takes a few years. Most school students do not want to go to university. Good for them. There's a place for everyone and their preferance

am: (preference)

certainly does not necesarily reflect their intelligence or ability but it also certainly will impact how and what they learn in future. Likewise, many photographers will not understand technical aspects of photography and even if they want to it will take a lot of pregressive training or teaching to achieve it. I'm sure that some of your readers are part way there already and can handle some technical info.

AM: Hope so but not me.

We've somehow gotten into some technical stuff here and the only signal we're getting is go away and keep it simple enough for everyone to understand it. I tried to simplify it but apparently not enough. If you want to keep all photographic discussions in the educational resources forum to a non-technical level at the lowest common denominator then that's fine but it will hardly enlighten those who might be interested and willing to pick up on technical or complex aspects.

AM: I simply would love to see stuff posted that folks can understand and apply. I would think that most of the stuff above is way beyond at least 99% of the folks here, and in addition, I do not see how understanding it would help anyone.

I apologise if I sound a bit short but I was only trying to help, as were the others.
AM: No problema; we are all trying our best.

We know that what we write is not for everyone but that doesn't mean it is fit for no-one. I'll steer clear of offering such input in future but unfortunately that limits what I can offer because I don't have your level of practical experience to draw on. I guess I'll be a lurker :)

AM: Above all else BPN is about images and about photography. You could always post an image. My experience over the past decade (and Robert O'Toole who is pretty damend good techinically is sitting here agreeing with me), is that all of the folks who spend their time on line spouting high level technical stuff (BS if you will) have either never taken an image or have yet to create one that is really good.

Later and love, artie

Roger Clark
03-29-2008, 11:48 AM
AM: Above all else BPN is about images and about photography. You could always post an image. My experience over the past decade (and Robert O'Toole who is pretty damned good techinically is sitting here agreeing with me), is that all of the folks who spend their time on line spouting high level technical stuff (BS if you will) have either never taken an image or have yet to create one that is really good.

That is an interesting claim. In my experience photographing along side many photographers in the field, many with whom I've gone to lunch and dinner with, and become friends with, are dominated by professionals (and interestingly quite a few dentists and retired dentists as well as engineers, scientists, medical doctors, etc). It is the professionals who have the money to buy the high end equipment needed for wildlife photography and the funds to travel to exotic places.

Then on the equipment side, the change from film to digital photography has added new technical issues that never previously came into the picture. Wildlife photography, especially action photography demands performance that in some cases is even beyond the capabilities of current cameras (e.g. speed of autofocus tracking). Understanding the fine details of technical capabilities allows one to push those limits (e.g.astrophotography with your telephoto lens and digital camera, or the high iso noise performance when photographing action before sunrise, which by the way are quite predictable with some technical knowledge).

I came to this forum so I could learn new things, and in return I hope I can impart some of the things I've learned.

I have hundreds (perhaps thousands--haven't counted) of published images, in both popular literature but mostly in scientific literature. I've even won a few national contests (I don't enter many) including best in show.

So what brought on the thread diversion was plate scale. You may think it is BS, but it does have uses. I gave the example that if you know the distance and the plate scale you can make measurements, like the wing spread on a bird. While that may not be important for making a pretty picture, it has uses from simple curiosity to scientific ecology.

Roger

Jan Walker
04-04-2008, 04:19 AM
All that having been said, I'd like to return to the original image since I'm new here. My first impression on seeing it was that the bird was too white.

Why did I think that? It was because of its relation to the background colors, which are more like those on a dull day. Except that the patches of actual blues have the color of a sunny day but the darkness of a cloudy day. In saying this, my perspective is from representational landscape painting where you (in one school at least) try to "capture the light of the day". Everything under the sun reflects the light of that sun, not a different one. So to make the image harmonious or "look natural" sometimes a white bird should really not be as white as possible even when it is in full sun.

Another impression. Because of its position in the image frame, the green shape really leaps out, even on the original. It is a startling color to encounter in nature. More often seen in crayons! And it gets even more glowing in the later images when it was lightened more. Should it have been lightened or not? Perhaps not because then the bird would look whiter even if not cranked all the way up.

Another way to think about this image: what if the subject of the picture is the color juxtaposition of the green patch and the beautiful yellow-orange of the beak and its gradations. That might suggest a different approach to the whites altogether.

Which is to say, white is being perceived in context. So adjusting it in context is appropriate, using one's knowledge of and sensitivity to the relationships of light and color in natural settings. If you change the bird, you also have to consider changing its context (as in the suggestion to lighten the sky also).

Apologies if this is well known and said elsewhere on the site. But it seemed to apply to the discussion of this image.
Regards-
Jan Walker

Arthur Morris
04-04-2008, 06:57 AM
Thanks Jan for adding your comments. One thing that the vast majority of folks do not realize is that when you have the correct exposure for bright whites, the middle-tones in that same image are one stop undrexposed... That is one of the many reasons for learning to make adjustments to selected areas of an image.

later and love, artie

Andrew George
04-04-2008, 12:30 PM
Besides all the Techs, why not choose the best result for yourself next to what gives the most atmosphere or whitebalance you like best or you saw at that moment, rather than be very technical about it. The beauty of (nature) photography is also the feeling you get from an photo or want to show. I'm struggling sometimes myself at the same discussion, but I learn more and more to go just on feeling....actually most photographic winners are spherical (to me)..think about it. I would go go for a rework in the middle of Leroy and Arthur.

dave v
04-04-2008, 04:07 PM
OK, I have a question.

Does any one know what the read out is for an egret feather?
Should it be 255,255,255, or something a bit lower?

When I "adjust" my shots, I just do what looks good to me, and for the most part, that's
to pull maybe not the most detail out of a shot, but the best details from it.

Leroy Laverman
04-04-2008, 05:29 PM
I think the short answer is that it should be whatever looks good.

With that said, if you have a large area reading 255,255,255 then it's generally considered 'blown out'. It may be that there is just no detail in that region but there's no one size fits all rule. If all the feathers are that bright then it's definitely over exposed but if some are that bright it may be fine.

Roger Clark
04-06-2008, 12:15 PM
Leroy,
I agree. Technically, there is no "255 255 255" in the real world. These numbers are simply a representation of it. (There is the science of reflectance, but we need not go there.)
Regardless of all the technical details, it matters not what the actual reflectance is, it matters how we perceive it. That is another reason why I posted the full moon image above,
http://www.birdphotographers.net/forums/attachment.php?attachmentid=8455&d=1206592207
The reflectance of the moon is around 10%, so darker than an 18% gray card. But you rarely see images of the moon as such a dark gray. The full moon appears very bright to our eyes, and I represented that in the image above. So Art's original egret image is not incorrect, as that may have been how it was perceived. However, people have expectations, and thus some may object when they see an expected white bird look gray, or an image of the moon look bright and almost white. So it really comes down to perception and the expectation of perception. Personally I think knowing a little of the technical details of human eye perception lets one pull out and present subtle details.

Roger

John Wilkerson
04-06-2008, 11:47 PM
Very interesting. I too have had problems with whites. This was very informative but man does my head hurt. All kidding aside. This went really deep but I still learned something. Thanks for sharing.