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Thread: The wonderful and missunderstood world of JPEG

  1. #11
    Barracuda
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    Those two images are not just close, but identical, pixel by pixel... and this represents a "compression" down to 4.8 meg... from the original 10 meg.

    But that is a lot bigger than Nikon, for example uses. So what happens if you go with more compression?

  2. #12
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    Next, I took the same chroma, and increased the compression up to 25% -



    This is the compressed one:



    The image size was down to a small 1.08 meg... and I can easily tell something has happened to it, but I don't know if someone looking could tell.. again, download and look for yourself.

  3. #13
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    Here is what happens if you keep going, down to 50% compression and a size of .4792 meg...

    Again the original versus the compressed one:




    And Compressed:




    This has some many JPEG artifacts, that I would never use it... how does it look to you?

  4. #14
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    The large picture, in the above example, has the sky with bands of light to dark... and as you can see, if you look closely, the image is getting blurry.. this is the problem with the DSLR JPEG's and why you need to use RAW with them.

  5. #15
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    Most of the comparisons were pretty close but the last one you could easily tell a big difference. Everything got really pixelated. I know from using photoshop and doing some graphic editing it is much easier to work with a high resolution image. You can alway compress it and reduce the size once you have finished working on the image, but you can't put in resolution that wasn't there to begin with. Not sure that this ties in to your posts, but something I have experienced from the enhancement phase of taking photos.
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  6. #16
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    Before going on, the information presented here has been staring all of the experts in the face for some time, just that no one has put the pieces together.. everyone has been to busy looking at the results, and not been spending time looking at why they are getting the results.

    Ok, off the soap box now.

  7. #17
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    Quote Originally Posted by RoadRacer1978 View Post
    Most of the comparisons were pretty close but the last one you could easily tell a big difference. Everything got really pixelated. I know from using photoshop and doing some graphic editing it is much easier to work with a high resolution image. You can alway compress it and reduce the size once you have finished working on the image, but you can't put in resolution that wasn't there to begin with. Not sure that this ties in to your posts, but something I have experienced from the enhancement phase of taking photos.
    It will in just a minute...hold on please.

  8. #18
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    I had pointed out earlier, that there were twelve differ Chroma subsampling methods... each will reduce the number of variables by a different factor...

    However, only 1x1 1x1 1x1 and 2x1 1x1 1x1 are commonly used, as reducing the others is easy for a person to see. Ideally, everyone is using the 1x1 1x1 1x1, but who know? Or is there a way to tell?

  9. #19
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    Well, there is a way... all you need is a picture taken with the camera, and a program that can do the jpeg compression. You take the image and compress it until it is nearly identical to the original compression, and you have it (there will be a slight difference, due to rounding of numbers and the exact math).

    So, back to the Nikon D200 image... what did they use? Turns out to be 6% (it shows a 4% compression, but 4 % does not yield the size they have) compression. Can you see 6%.. not very well... only in the finest of detail could you tell. Guess what? That is what they are seeing when they look at raw versus JPEG from that camera. No magic, nothing fancy... just what you should see.
    Last edited by Puffer Fish; 11-24-2007 at 20:56.

  10. #20
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    What about the Fuji f50? First off, that 6% is a very common compression... the F11 I have, uses the same amount. But that is not the case with the f50, it uses (again, it shows 3.2), but measures something around 2 (there are a lot more subtle adjustments that each company can make, so the information here is just approximate. The type of scanning it does also effects the size a bit...but has no effect on quality.

    Does this loose some information - yes it does, but only a very, very small amount, and looking at the detail, there is some damage, but no loss of information.. resolution appears to be intact.

    Here is an original tiny section:



    A two percent compression:



    And for comparison, a 6% compression"



    You will have to blow this up a great deal to see the difference... but it is there...

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