View Full Version : Rendering "red" correctly - is it possible?

Ed Okie
02-06-2008, 11:53 AM
If there is one color that continues to drive me nuts in terms of metering, exposing and rendering correctly in post-processing - it is red. The digital camera, Canon 5D in my case (but by no means limited to that camera... all digital sensors apparently are afflicted with this "disease") red will easily - if not often - jump off the right side of the histogram scale. Determining "blown" highlights is tricky at best, totally evasive when shooting Raw (until after-the-fact when computer processing). The camera's LCD back-panel viewer is about worthless; Histogram set to reveal RGB colors only shows that a red-Jpeg is off the right side. The camera's blown-highlight flasher doesn't signal any warning for red... only if the luminescence reading jumps off the high end, and that's strictly with Jpegs.
How do we zero in on red? Or, is there any - in front of the lens - valid correction filter that would tone down red (and not affect green and blue)? Excessive sensitivity to red by the sensor appears as the underlying culprit. Canon engineers have avoided the subject for years.
Azalea flowers (attached) is but one example, sandhill cranes with their red heads, orange-pink pylon barrier race cones, day-glo fishing bobers are other examples.

Fabs Forns
02-06-2008, 12:01 PM
Ed, blown reds are not only frequent in Canon, but in other manufactures also. It is a fault of digital that I hope will eventually be taken care of.
Blown reds obscure detail and what we do about it is basically go to Hue/Saturation and de-sat the reds a little bit to let the detail show.

I'll be willing to hear other ways....

Ed Okie
02-06-2008, 01:07 PM
Babs, Hue/Saturation changes certainly help modify reds. I virtually always set the camera at -1 or -2 for Saturation when shooting Jpegs (plus contrast at -4). But if the underlying red color is blown at sensor-level... there ain't no recovery! Creating something out of nothing isn't possible. How do we keep ourselves from falling off that cliff? Yes, we can fake it by toning down reds or whites (adding gray)... but that's not adding nor capturing detail.

Jim Poor
02-06-2008, 01:10 PM
What about channel mixing the B&G to output to R?

I know that is still a post capture solution, but . . .

john crookes
02-06-2008, 06:25 PM
Hi Ed
what are your settings in the camera
If you are shooting jpeg i would at least set you color to adobe to give you as much possible as you can get
if in raw not as vital as you can open in prophoto and then convert to srgb for the web

Fabs Forns
02-06-2008, 08:06 PM
I always used RAW in Canon and now use RAW in Nikon, and very few times my reds were so bad that there was no way back. when I see over reds, just go back a bit in the red sat and the detail is back. Now, if you over blow like when you cook the whites, there's certainly no way back.

Alfred Forns
02-07-2008, 08:47 AM
Ed after the conversion go to image>adjustments>hue/sat> in the master drop down to reds and decrease saturation Would not make any settings in camera

Ed Okie
02-07-2008, 11:01 AM
I'll bite, Al... why not tweak at camera level? Yes, in raw it's a non-issue (other than how it displays on the LCD), but Jpegs remain a viable file format. In studio shooting with strobes I always tweak the camera-color to deliver "perfect" RGB readings as measured off a calibrated white or gray card. (CC Green +4 is the winning number for my softboxes on WhiteLightning strobes). Once that and overall exposure is dialed in - repetitive product shoots are a dream come true (Jpegs deliver top notch results).
Outdoor shooting in difficult or highly variable situations, raw is a god-send; jpeg can't compete. In normal outdoor situations jpegs are often very suitable. But even raw files deliver grief if the color red unknowingly is blown. Toning it down "after conversion" with image>adustments>hue/sat does veil that problematic area but it doesn't get detail back.
If we could get the RGB colors more in tune with each other at camera level, everyone would get more realistic results, i.e., the "base foundation" would provide a more level starting point for adjustments if desired; now, we're always trying to go in "after the fact" and apply the band-aid or tourniquet.

Alfred Forns
02-07-2008, 12:05 PM
Ed you hit the nail on the head In control conditions it would work I remember while developing slides I would do strips Just taking a few from the end and running it Base on results might push/pull one third stop This would be with shoots under same light etc

If you decrease the reds across the board in the jpeg what happens when you have a tone that is not red but has red? It will not look true to form Also reds will behave differently according to the light source Both intensity and temperature

Also not all the reds have to be worked on In the bird images there are some universal one Example Cardinals Normally you need back down the red channel Lots of other red birds you do not have to do so

I don't see it as an after the fact procedure Not sure that you could eliminate in camera without affection others in a negative way

Ed Okie
02-07-2008, 04:12 PM
...Also reds will behave differently according to the light source Both intensity and temperature

Absolutely is true - red/pink azaleas in sunshine are near impossible to render reasonably well. Same flower/bush in overcast or at twilight (effectively being bombarded by blue light)...seldom a problem.
Red apparently is the only color that reacts with such dramatic and irregular difference - light intensity and temperature apparently can create red-luminescence, almost that "glow-in-the-dark" effect.
I, like you, am in Central Florida, now about the peak of the red/pink azalea flower season. Majority of others around the nation are probably wondering what in the heck are we're talking about! Flowers?

An aside on birds: for whatever reason birds in my area are noticeably missing this year, relatively speaking - none compared to throngs in prior years. Haven't a clue where they've gone, have never seen a year like this. A lesser population of sandhill cranes are around, but oddly, they're still in groups of 3 or 4, the parents haven't gone off on their own to lay eggs to start a new family. Definitely behind schedule.

Jared Lloyd
02-24-2008, 09:50 AM
I havn't had nearly as much trouble with reds as I have with yellow. For the life of me, I cannot get a true rendering of this color. It either blows out or it is a muddied orange.

Noel Carboni
02-24-2008, 12:25 PM
I've discussed this with Ed for a while, but I'll share my thoughts here as well. Understanding at least part of why it's happening may help us all work around the pitfalls...

Some facts and thoughts:

The anti-aliasing / infrared block filter in front of our sensors (Canon at least) is blue-green colored. That means it's blocking more red light than other colors.

Because of the above, the programming (in the camera chips or on the computers) has to compensate for lower readings from the red photosites by boosting the levels at some point in the processing.

Boosting red channel readings also results in more noise in the red channel.

Canon (and possibly others) in their conversion process seem to have implemented some kind of red channel blurring to compensate for this. Any photo of a bright red object suffers a tremendous loss of detail. You can easily see this in in-camera JPEGs. Fortunately, the Camera Raw converter in Adobe Photoshop does not exhibit this effect.

If taking bright exposures, and considering the blue-green filter, as you might imagine the green and blue channels overexpose first (I've confirmed this with Thomas Knoll, author of Camera Raw for Photoshop). This is why some people claim the raw converters offer "headroom", in which slight overexposure can be compensated for. In some cases, with one or two saturated color channels, the converters can indeed bring back some detail by extrapolating from the third.

The sRGB color space does not provide for as much red color representation as others, though with modern equipment (monitors/printers) some pretty vivid red colors are achievable. However, this color gamut limitation affects how many of the converters work. Apparently, some of the raw conversion software writers have made the decision to jam the output levels to max or min instead of making the converted data fit into the output space. They may be in the pursuit of "accuracy" in this endeavor, but frankly they're shooting us all in the feet. Notably Canon does not do this with the in-camera JPEGs. Take a photo of a sunset in which the sun is present and try differnt conversions (and compare to the in-camera JPEG) and you'll see what I mean.

There has been some conjecture that not everyone sees the color red with as much vividity as others. Is it possible the people who set the parameters for rendering this color unnaturally boosted it so that it looked better to them?

There are settings in Camera Raw for Photoshop in which the red color can be toned down - desaturated, made less luminous, etc. - but there seems to be no one setting (Ed will back me up on this) that works for every case. If you're shooting bright red things you'll have a little more work to do tweaking settings to get your images to look just right.


I've had the best luck shooting raw and using the Adobe Photoshop Camera Raw function to convert images of bright red objects, retain the maximum detail, and keep from having fluorescent looking red colors in my images.


Jan Walker
02-24-2008, 04:51 PM
The most recent camera I bought had a default setting that included something called "vivid" for the light. This setting cranked up the saturation, an effect that many consumers love so cameras come to you that way. I take jpegs and on some cameras turn the contrast and saturation all the way down.

In another vein, is it possible that your camera's white balance settings contribute to this effect Starting with whites that are white is a major step forward in the color adjustment realm... I've finally given up on custom white balance in-camera because my camera (Olympus) needs you to shoot a piece of neutral media for the custom exposure. Instead, I got an Expo Disk, which is basically a filter that turns the incoming light into monotone. Then you shoot the custom white balance wtih that over the lens. (Check out the various equipment fora; not everyone thinks that these are worth the money although I'm a convert, for the convenience.)

Ed Okie
02-25-2008, 10:03 AM
JL - your "yellow" problem - what camera are you using? I test shot yellow jasmine flowers (Canon 5D, 100mm macro) and the only post-processing method of turning yellow into orange occurs with appreciable over-saturation. Original exposure, though, is a big part of color rendering... over-exposure will kill you - if it runs off the right side of the histogram it's basically history.

Jared Lloyd
02-25-2008, 10:33 AM
Ed, the yellow problem was occurring with a Nikon D100. I recently purchased the D300 and have yet to test this. Considering Noel's comments, yellow falls within the red spectrum of light and therefore should be subject to the same issues right?

Ed Okie
02-26-2008, 11:44 AM
JL - the tech stuff, Noel is "the most expert" of any of us in this department, his background is that of a computer engineer, now combined with photo software skills at a high level, plus well-qualified in picture taking ability.
Red, though, is the one color that always seems to "jump out" when colors go astray. Over-emphasis at red-rendering has been around for years, same as it has been the problem-child with TVs.
Your point is well taken, all colors can certainly act up - somewhat based on the subject we are shooting, the dominant colors that prevail within that image.
The only correlation I've come across, whatever the color, is that of over-exposure at camera level. Once (whatever color) falls off the right-side cliff, there ain't-no way back. Despite what Raw purist claim. Gone is gone. Partial recovery, or simulations of recovery is the actual outcome... not the real thing recovered.
Does your Nikon behave significantly different than the Canon? I have no idea nor experience. Canon does have, and has had, a significant problem rendering reds correctly. Why Canon engineers haven't tweaked their wizardry-algorithms to accommodate this oddity... I have no idea.
Where I recently have seen reds go dramatically astray is with red flowers (I'm in Florida, now the peak of bloom season). Areas of red petals over-exposed (or pushed to far in post-processing) will dramatically change to lavender-purple.
Most confusing: read that lavender spot-area with monitor software in terms of RGB levels... and not one level is near the 255 reading! Yet, at the same instant the histogram's red line rocket's upward and out on the right side. Net, net: one numerical control is saying "everything is fine," the other (line) saying ouch! The Ouch-line is correct.
Possibly this "yellow to orange" problem is occurring on your end at the software stage. But if it occurred at the camera-shooting stage, you overexposed the image or that color area... you're basically dead in the water.