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Thread: Jpeg file size

  1. #1

    Default Jpeg file size

    just a noob question.. I normally shoot with my GF1 12MP FINE and the file range from 5-9MBs, and resizing it to jpeg to 90% quality makes it abt 1-3mbs, just wondering, any one know why is there such a drastic difference, and will the reduced quality affects my prints? thanks!

  2. #2
    Moderator ortega's Avatar
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    Default Re: Jpeg file size

    if you don't pixel peep, then no, not much visible difference

    why not try it out

    open your file, save as - different name - different compression setting
    do again for different settings

    then print out and see

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    Default Re: Jpeg file size

    It's the encoding algorithm..
    similar colors are identified and encoded to reduce file size.. which will introduce artifact at lower quality settings.. you can see some color banding..

    see this chart from wiki..

    You can replicate this by saving a 12mp photo, and saving another one which is a 12mp all picture.. notice the second is only a few kb?

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    Default Re: Jpeg file size

    Quote Originally Posted by viix View Post
    It's the encoding algorithm..
    similar colors are identified and encoded to reduce file size.. which will introduce artifact at lower quality settings.. you can see some color banding..
    No, JPEG does not employ perceptual color similarity detection. The banding which one observes is the result of severe quantization of 8x8 pixel blocks (DCT coefficients actually). this results in only the DC coefficient being retain for storage in the file data. hence each 8x8 block assumes the average color data with no details. this is the same effect in video coding (MPEG, H.264), in which to some extend, loop filtering (deblocking) is used to smooth out the "banding" artifacts.

    additionally, if your image contains grain noise or shot noise, it is highly recommended that you save in highest (ONLY) quality setting. other wise, the same quantization process will try to remove your noise (high frequency) and result in "ringing" artifacts.

    Otherwise, attempt to denoise your image first before saving in lower quality settings.
    我吔呢班打工仔, 一生一世為錢幣做奴隸 flickr

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    Default Re: Jpeg file size

    Quote Originally Posted by leews2001 View Post
    No, JPEG does not employ perceptual color similarity detection. The banding which one observes is the result of severe quantization of 8x8 pixel blocks (DCT coefficients actually). this results in only the DC coefficient being retain for storage in the file data. hence each 8x8 block assumes the average color data with no details. this is the same effect in video coding (MPEG, H.264), in which to some extend, loop filtering (deblocking) is used to smooth out the "banding" artifacts.

    additionally, if your image contains grain noise or shot noise, it is highly recommended that you save in highest (ONLY) quality setting. other wise, the same quantization process will try to remove your noise (high frequency) and result in "ringing" artifacts.

    Otherwise, attempt to denoise your image first before saving in lower quality settings.
    ah sweet! Now I know

  6. #6

    Default Re: Jpeg file size

    Quote Originally Posted by ortega View Post
    if you don't pixel peep, then no, not much visible difference

    why not try it out

    open your file, save as - different name - different compression setting
    do again for different settings

    then print out and see
    yeah, even when i peep, i cant really see the difference in the image. maybe i shd print out and see the diffrence. thanks!

    Quote Originally Posted by leews2001 View Post
    No, JPEG does not employ perceptual color similarity detection. The banding which one observes is the result of severe quantization of 8x8 pixel blocks (DCT coefficients actually). this results in only the DC coefficient being retain for storage in the file data. hence each 8x8 block assumes the average color data with no details. this is the same effect in video coding (MPEG, H.264), in which to some extend, loop filtering (deblocking) is used to smooth out the "banding" artifacts.

    additionally, if your image contains grain noise or shot noise, it is highly recommended that you save in highest (ONLY) quality setting. other wise, the same quantization process will try to remove your noise (high frequency) and result in "ringing" artifacts.

    Otherwise, attempt to denoise your image first before saving in lower quality settings.
    Thats enlightening info thanks, So does process from RAW and to jpeg with 90% quality setting results in the 'ringing' as you mentioned? or just with normal jpeg 100% to jpeg 90% quality?

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    Default Re: Jpeg file size

    Quote Originally Posted by GFhana View Post
    So does process from RAW and to jpeg with 90% quality setting results in the 'ringing' as you mentioned? or just with normal jpeg 100% to jpeg 90% quality?
    Yes, it will. 'Ringing' artifacts is a simple phenomena in signal processing. (see http://en.wikipedia.org/wiki/Ringing_artifacts, http://www.stat.columbia.edu/~jakuli.../artifacts.htm). but in terms of visual perception, other issues comes into play such as 'visual masking'. so there is no guideline of what quality jpeg u saved in will make your picture ringing-free.

    ringing begins once you save anything in jpeg. (or other lossy format) the question is how visible they are in EACH of those picture.
    我吔呢班打工仔, 一生一世為錢幣做奴隸 flickr

  8. #8

    Default Re: Jpeg file size

    Quote Originally Posted by GFhana View Post
    just a noob question.. I normally shoot with my GF1 12MP FINE and the file range from 5-9MBs, and resizing it ....
    How much are you resizing? What are the original pixel dimensions, and what are the downsized dimensions?

  9. #9

    Default Re: Jpeg file size

    Quote Originally Posted by Peano View Post
    How much are you resizing? What are the original pixel dimensions, and what are the downsized dimensions?
    4000x3000 just trying to change quality setting to get the size down, also wonder does everyone keep the full 100% quality pics on their machines?

  10. #10

    Default Re: Jpeg file size

    Quote Originally Posted by GFhana View Post
    4000x3000 just trying to change quality setting to get the size down, also wonder does everyone keep the full 100% quality pics on their machines?
    If you're going for prints and are using Photoshop, use "Save As" and quality level 10. There's no point in going above 10. Don't worry about the file size unless you're saving for the web. Keep as much image data as you need to get a decent print.


  11. #11

    Default Re: Jpeg file size

    Quote Originally Posted by Peano View Post
    If you're going for prints and are using Photoshop, use "Save As" and quality level 10. There's no point in going above 10. Don't worry about the file size unless you're saving for the web. Keep as much image data as you need to get a decent print.

    So if my photoshop cs2 only have 1 - 10? guess i will keep the maximum file size for the crucial ones then.

  12. #12
    Senior Member limwhow's Avatar
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    Default Re: Jpeg file size

    Quote Originally Posted by Peano View Post
    If you're going for prints and are using Photoshop, use "Save As" and quality level 10. There's no point in going above 10. Don't worry about the file size unless you're saving for the web. Keep as much image data as you need to get a decent print.
    Interesting point, Peano.
    And if we choose max quality in PS CS4 of level 12?
    May I ask why is there no point in saving above the level of 10?

  13. #13

    Default Re: Jpeg file size

    Quote Originally Posted by limwhow View Post
    Interesting point, Peano.
    And if we choose max quality in PS CS4 of level 12?
    May I ask why is there no point in saving above the level of 10?
    You can't see any difference above 10. Professional labs (like White House Custom Color) recommend a quality level of 10. Above that, all you get is a bigger file.

  14. #14

    Default Re: Jpeg file size

    i always save at quality 12

    it's not the big a difference in file size anyways with terrabytes flying around these days

    beats the hell out of saving in tiff or psd, now those are scary

  15. #15
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    Default Re: Jpeg file size

    Quote Originally Posted by night86mare View Post
    i always save at quality 12

    it's not the big a difference in file size anyways with terrabytes flying around these days

    beats the hell out of saving in tiff or psd, now those are scary
    actually with terrabytes flying around, i save in psd

    I dun usually save at 12 unless it is for print purposes. otherwise usually ard 8 or more works for web display purposes.

    leews2001, thanks for the good read

    ryna

  16. #16

    Default Re: Jpeg file size

    Quote Originally Posted by giantcanopy View Post
    actually with terrabytes flying around, i save in psd
    i have no terrabytes yet :P

  17. #17

    Default Re: Jpeg file size

    Quote Originally Posted by night86mare View Post
    i always save at quality 12

    it's not the big a difference in file size anyways with terrabytes flying around these days

    beats the hell out of saving in tiff or psd, now those are scary
    I don't agree, but I do commercial work. Many a time, I was so glad I had saved .psd files with all layers intact -- and I do save all of them.

    Concerning jpeg and quality levels, here is what White House Custom Color (a pro lab) says:


  18. #18

    Default Re: Jpeg file size

    Well, this is a interesting thread! Anyway, lesson of the day:
    save in TIFF/PSD, print in JPG.

  19. #19

    Default Re: Jpeg file size

    Quote Originally Posted by whattokingu View Post
    Well, this is a interesting thread! Anyway, lesson of the day:
    save in TIFF/PSD, print in JPG.
    Unless you need a tif for some special purpose, it's sufficient to save just the psd. From that, you can always generate a copy in any format you like -- jpeg, tif, gif, png, etc.

  20. #20

    Default Re: Jpeg file size

    Quote Originally Posted by Peano View Post
    I don't agree, but I do commercial work. Many a time, I was so glad I had saved .psd files with all layers intact -- and I do save all of them.

    Concerning jpeg and quality levels, here is what White House Custom Color (a pro lab) says:

    i keep raw files for pictures i think i want to rework.. if need be then do from scratch

    well, i do have the habit of working on jpg files again, so quality 12.. maybe it cannot be seen in "print", but is there a chance that there is degradation if you save in 10 versus 12?

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