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Thread: JPEG Compression

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    Lifetime Member Jay Gould's Avatar
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    Default JPEG Compression

    On the infamous and exceptionally fabulists BAA Blog, Artie commented on preparing jpegs for web presentation: http://www.birdsasart-blog.com/2011/...#comment-97545

    When questioned about poor image quality more than a few folks on BPN complain about the 200kb file size limit. I am always baffled by these comments and I never have a clue as to what folks are doing that causes their image quality problems.
    I commented:

    Artie, most of the time I see the complaint about the 200 limit in relation to landscapes; not avian. Is there a difference in the amount of information in a landscape image that causes landscape images to suffer from jpeg compression ore so than images of single birds. This would be an interesting discussion in the Workflow Forum. Cheers, and thanks forthe 96dpi information.
    What are your thoughts?
    Cheers, Jay

    My Digital Art - "Nature Interpreted" - can now be view at http://www.luvntravlnphotography.com

    "Nature Interpreted" - Photography begins with your mind and eyes, and ends with an image representing your vision and your reality of the captured scene; photography exceeds the camera sensor's limitations. Capturing and Processing landscapes and seascapes allows me to express my vision and reality of Nature.

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    BPN Viewer Charles Glatzer's Avatar
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    Jay, very fine detail usually requires higher res and less compression for best viewing. That said, quality also depends on the method of compression, sharpening, etc. Btw- have you ever checked the quantity of images you can fit on a card when you change from a low ISO to higher ISO. Moreover, not all images are recorded equally regardless of the cameras mega-pixel rating. Check the images sizes produced out of the camera for different ISO of the same scene and/or with images containIng many tonal values vs those of mostly similar values.

    Best,

    Chas

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    Quote Originally Posted by Charles Glatzer View Post
    Jay, very fine detail usually requires higher res and less compression for best viewing. That said, quality also depends on the method of compression, sharpening, etc. Btw- have you ever checked the quantity of images you can fit on a card when you change from a low ISO to higher ISO. Moreover, not all images are recorded equally regardless of the cameras mega-pixel rating. Check the images sizes produced out of the camera for different ISO of the same scene and/or with images containIng many tonal values vs those of mostly similar values.
    Chas,

    I assume you mean file sizes, not image sizes. On all my cameras, image size (number of pixels) is the same as a function of ISO, but file size increases with ISO due to the increased noise that the JPG compression must work with.

    To Jay's original question, yes I have seen ths especially with landscapes. Jusy last night I was preparing a landscape image and at only 900 pixels across, the file size was over 300 KB as quality 67% and at about 50% quality it was 184 KB. Here is the image, which I will not post on BPN because I can't make it fit reasonably within the 200 KB limit without making it much smaller or sacrificing quality:
    http://www.clarkvision.com/galleries...105.b-900.html
    All those waves and the high contrast imaging into the sun create a lot of fine detail that the jpeg compressor has a hard time with. The above image 312 KB saved at something like 67%.

    Here are the file sizes:
    67%: 312 KB
    53%: 227 KB
    51%: 222KB
    50%: 184 KB

    Note the slow drop until 51% then a big drop and a noticeable change in image quality occurred from 51 to 50%.

    Roger
    Last edited by Roger Clark; 09-19-2011 at 07:26 AM.

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    Jay- Following from Chas' thoughts- the way jpeg compresses images means that small-scale detail in an image requires more information to render an image in compression than areas of little detail. If you take a typical bird portrait on BPN with a nice smooth, low-noise background and a high-detail, sharp subject taking up say 40% of the image real estate, the file can easily be compressed to under 200kb with using a very high quality compression setting (80-90% in Ps Save for Web and Devices). To answer your question- there usually is a lot more fine-scale detail in a landscape image because that level of detail often covers the entire image area or a large part of it. A nice, sharp landscape image with lots of detail from stem to stern may require a compression level of <50% to get under BPN's 200kb limit. Noise contributes to small-scale detail so noise reduction can help to allow a higher-quality compression for the same file size. Having said this, at screen resolutions, in my experience, you have to compress pretty severely to see a really noticeable degradation in IQ.

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    BPN Viewer Charles Glatzer's Avatar
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    Roger,

    Thanks, and yes... I meant file size ;~)

    Best,

    Chas

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    Default For those that knows!

    in the compression of jpegs at BPN, when a file is submitted at 1024X800, is there a difference between a 24meg and a 12 meg camera file's submission?

    Rob............

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    Lifetime Member Jay Gould's Avatar
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    Guys, it appears we are all on the same page when it comes to jepg compression: easier to maintain high quality sharp detailed avian images with the 200kb limit than it is with landscape images.

    I post my images both here and on Nature Scapes which has a 250kb limit with an 800 long side limit. My general observation is that the same image posted at 200/1024 and 250/800 is sharper at the Nature Scapes limits than at the BPN limits.

    Having said that, I will continue to post on BPN in all Forums; hopefully, the Owners will be able to replace Roman and Dave with Landscape Photographers with similar qualities and a commitment to give of their time to share and teach.
    Cheers, Jay

    My Digital Art - "Nature Interpreted" - can now be view at http://www.luvntravlnphotography.com

    "Nature Interpreted" - Photography begins with your mind and eyes, and ends with an image representing your vision and your reality of the captured scene; photography exceeds the camera sensor's limitations. Capturing and Processing landscapes and seascapes allows me to express my vision and reality of Nature.

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    Attached Images Attached Images
     
    Would linking to the image on an external website be a solution to overcome posting the occasional landschape image above 200 kb? When you are not a BPN member, this is the only way to post images. As long as there are no limits provided by the website that hosts the original image (Flickr, or your own site for instance), I think this would work. My guess would be that file size limit is only an issue when uploading an image to be hosted on the BPN server, but please correct me if I'm wrong.
    Btw I recently posted a landscape image with very much fine details, which I had to compress below 50% to meet the 200kb limit. This amount of compression caused all kinds of artifacts to appear in the sky, which were not there above compression of 55%. Whether or not this will happen will probably also depend on the quality of the original image and the camera used. Since Arthur has very good technique and shoots the 1D, I guess he's not likely to run into trouble (which maybe the point of his remarks).
    Here's an enlargement of a piece of sky from this post (http://www.birdphotographers.net/for...71-Lonely-tree). Left is the 'Save for web' version at 100% quality, 1000px wide, size of the whole image 949 kb, right is 'Save for web' at 46%, also at 1000px wide, just meeting the 200 kb limit (file size 204 kb).

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    Quote Originally Posted by Jerry van Dijk View Post
    Would linking to the image on an external website be a solution to overcome posting the occasional landschape image above 200 kb? When you are not a BPN member, this is the only way to post images. As long as there are no limits provided by the website that hosts the original image (Flickr, or your own site for instance), I think this would work. My guess would be that file size limit is only an issue when uploading an image to be hosted on the BPN server, but please correct me if I'm wrong.
    Btw I recently posted a landscape image with very much fine details, which I had to compress below 50% to meet the 200kb limit. This amount of compression caused all kinds of artifacts to appear in the sky, which were not there above compression of 55%. Whether or not this will happen will probably also depend on the quality of the original image and the camera used. Since Arthur has very good technique and shoots the 1D, I guess he's not likely to run into trouble (which maybe the point of his remarks).
    Here's an enlargement of a piece of sky from this post (http://www.birdphotographers.net/for...71-Lonely-tree). Left is the 'Save for web' version at 100% quality, 1000px wide, size of the whole image 949 kb, right is 'Save for web' at 46%, also at 1000px wide, just meeting the 200 kb limit (file size 204 kb).
    Hi Jerry- A resounding no from me on that one. Guideline 18 specifies the image size limits and they apply whether you are a member uploading to BPN or a Participant linking to a hosted image. This creates a level playing field for all and standardises the way images are presented to BPN viewers.

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    BPN Viewer Tom Graham's Avatar
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    FWIW, I also have not posted images because I could not accept the quality at less than 200KB. Even when I lowered px size to 960.
    Especially when ever image here is very closely scrutinized for IQ. The first and last thing that is "picked on". Sorta back to what Jay said his OP.
    Tom

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    OK John, I stand corrected! Makes a lot of sense.

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