JPG conversion problems

Discussion in 'Digital Darkroom' started by tar heel, Oct 17, 2009.

  1. Photoshop CS4 (Vista) is changing the resolution of my files when I convert to JPGs. It always changes to 72PPI and I want it to stay at 300ppi. I cannot figure out how to do it. I went to preferences, but could not find anything to change in the settings.
  2. how are you converting? There are many ways to do it and not knowing which you are using gives us no clue.
  3. Spearhead

    Spearhead Moderator

    The ppi doesn't matter until you print, at which time you will probably have to change the settings anyway. It's a header instruction, not something that affects the image file in any way.
  4. Save for web as jpeg forces files to become 72dpi, if that's how you're saving. PS help seems to suggest that choosing 'maximum' for quality avoids this, but it doesn't change anything for me in CS3.
  5. Spearhead

    Spearhead Moderator

    There's no reason to force it to anything, Adobe has always done this because a long time ago, graphic designers came from the print industry and sized things for web output in inches. Really pointless.
    JPG quality has nothing to do with resolution.
    Let's try this one more time.

    PPI is PIXELS PER INCH. INCH. There are no inches in digital files. That's why it's irrelevant.
  6. The OP is a professional photog and I imagine understands resolution. If I read his question correctly he is trying to understand why Photoshop is behaving in an unexpected fashion and how to achieve his desired output settings.
  7. If Photoshop's "save for web" is changing the DPI setting, maybe try "File|Save as" instead? Ensure your file is 8 bit first, PS won't change it for you, or let you know the problem. If you're trying to batch convert this may not work as well, though.
    Also, consider one of the cheaper viewer programs for jpeg conversions? Likely easier for batch.
  8. Spearhead

    Spearhead Moderator

    It doesn't matter why it is changing. Unless it's going to print, the output settings that matter are the pixel dimensions and the compression.
  9. Jeff, maybe it is changing to 72 dpi at his size in inches--which does matter! -- I don't think we have enough info to start arguments or to answer the question.
  10. Spearhead

    Spearhead Moderator

    He can always set it to 300 when he goes to print. It doesn't really matter what it is until he goes to print.
  11. if you have a file that is 8x10 at 300 in PSD and you change to a jpeg and it goes to an 8x10 at 72, yes it does matter! We don't have enough info as to what is going on.
  12. The OP hasn't specified whether it's being resampled. In any case, save for web doesn't change pixel dimensions, only resolution.
  13. He can always set it to 300 when he goes to print. It doesn't really matter what it is until he goes to print.​
    The PPI info included in the file does not make any sense.
  14. Regardless of how insignif. the DPI setting is, the OP doesn't want it changing. That should be doable.
    Personally, I would just do the conversion in ACDSee. Irfanview works similarly, I think:
    Select files you want converted to jpeg. Verify destination folder as required, etc, etc, and then click ok:
    Jpeg files are created, DPI settings are left as is, simple.
  15. Not to add any fuel to the fire, but I want to point out a time when the embedded dpi was important, regardless of the fact the file was the same at many-inches @ 72 dpi and few-inches @300 dpi: We deal with schools and I can't say that all yearbook advisors are top-notch at computer stuff. The yrbk program would only accept images at 300 dpi, regardless of the size. WE had to convert each image from 72 dpi, which is native for the image, to 300 dpi so the printer's program would accept the file for print. No, it didn't matter that it was the same file, and that little embedded number did make a difference. So there are times when changing that number in the the file itself, even if its just going on a cd, is important.
    To the OP, I've gone in to image size and changed it from 72 dpi to 300 dpi then went to image, save as, jpg, 12. This kept the "300 dpi" but I was using CS3 in XP.
  16. I am saving by "Save for web and devices". This file is indeed going to print, so I want my resolution to stay at 300ppi. I do know about changing my TIF file to 8 bit and then "save as" to Jpg. but why is "Save for web and devices" changing the ppi? CS3 does not do that.
  17. I am saving by "Save for web and devices". This file is indeed going to print,​
    Why use Save for Web then?
    My PS CS3 does change the ppi when using save for web, changes it to 72 under all settings
  18. If you are going to print, you should use the "Save As..." command and select "JPEG" in the pull-down menu for Format. That will maintain the dpi setting in your jpeg file.

    "Save for Web and Devices..." is meant to create files that are to viewed in web browsers and other screen devices.
  19. The yrbk program would only accept images at 300 dpi, regardless of the size​
    You can suggest that if they want to be professional on printing, remove this requirement.
    This requirement show they don't know what PPI value means and how a printer works.
    DPI is a different value. It may be the same number of PPI for contone printers, but it is Dot Per Inch in any case.
    Calling DPI what is PPI give the exact value of the printing scarcity of knowledge.

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