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  1. #1
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    I know you lose quality when you resave a jpeg, but sometimes the image you prepared a while back needs a change. When I open the jpeg in Photoshop the 40k file opens as a much bigger file. That's a good thing. But what is the BEST PROCEDURE for making the adjustment and then re-saving to use the image in the web layout? Here's what I do: I open the jpeg in Photoshop, save it as a photoshop file. Now it's big. Make the adjustment, save again, (adding .1 or quelquechose to filename) and it's still "big." Then I Save to Web. But that's when I'm in a QUANDARY, use Maximum 80 or even 100? Or strive for the low k figure the file had before I altered it? Don't I lose more detail when recompressing a file that was a jpeg to begin with? I'm using Mac OS9 if that means anything. Also, I'm obviously not a software engineer. What is Photoshop doing when it opens the Jpeg and gives me this bigger file, I didn't ask it to be bigger. Is photoshop restoring something? My photos are "make do with" material to begin with, not exactly works of art... But detail is detail, that's what we fight for, right?

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  3. #2
    Senior Member glyakk's Avatar
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    Quote Originally Posted by scribble2me
    I know you lose quality when you resave a jpeg, but sometimes the image you prepared a while back needs a change..
    This is why you should save the working photohsop file to make changes.
    Quote Originally Posted by scribble2me
    When I open the jpeg in Photoshop the 40k file opens as a much bigger file. That's a good thing.
    This does not mean the image quality has been impoved in anyway, you still have all the artifacting that was there befor you brought it into photohsop. The reason why the file size has increases is photoshop has 'prepped' the file as a temporary editable file that it stores in memory. I am assuming you are getting the file size from photohsop.

    The filesize you see at the bottom of the photohsop shows two things.. the left value is the size of the document as if it were flattened and sent to a printer, the right is the size of the document as if it were written as a full photoshop file and saved to disk. The only problem is counts a byte as 10 instead of 8. So if your jpg said Doc: 50k/1M you would actually transmit only 40Kb to your printer and the file would actually take up 800Kb of space if saved to your hard drive as a PSD.

    A jpg is a bitmap image. what that means is its made up of individual pixles that hold information about itself. It does not retain any information of its previous life as a photoshop file. And photoshop does not 'remember' what it used to look like. So when you open it again photoshop treats as if it were a pristine new image.

    Let me explain the process of opening a jpg in photohsop and than saving it again as another jpg. When you open a jpg in photoshop it goes to memeory(or scratch disk) where it gets some added functionality so you may edit it. Photohsop enables it to hold layers, alpha channels, color information etc.. But dont forget you are starting with an already degraded file, and photoshop does not know that the stray miscolored pixles(known as artafacts) are not part of the image you want. So after you make your changes to the file you go to save it as another jpg. Photoshop than process the image as if it were any other regular photoshop file. So you gain more artifacts on top of the ones you already had. This is why its not a good idea to edit jpg's. You should keep the orgional file so you may make any edits and create a whole new jpg.

    So yes you do loose even more detail when you turn a jpg into another jpg. Increasing the quality will not do anything to enhance the quality of the image, it will just prevent any more artifacts or other imperfections to litter your image. But it will increase your file size. So you have to play a balancing act, you can try to achive a lower file size but you will hurting image quality that much more. Or you can increase quality and try to 'breakeven' and end up with a file over 120Kb.


  4. #3
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    UR so nice. So, yeah, I'd like to just let the jpeg open pixel for pixel, make the change, and seal it back up again. Is there a way to tell Photoshop, 'Dont assume anything, just alter what I tell you.' ? Often the change is just a crop, or something easily so minor. Thanks for the review, added functionality, doesn't know artifact from imagefact. got it. Is there a Keep It Simple button in photoshop?

  5. #4
    Senior Member glyakk's Avatar
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    As far as I know there is no way you can do this.. You would have to edit it without opening it in any way and technically speaking that is impossiable. A jpg is a compressed file and when you open it, it decompresses so any changes you make to it in that state will effectivly 'distroy' its compression and it will have to be recompressed.


  6. #5
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    I understand SO much better now. Not the same snake when you push it back in the peanut can...


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