Decreasing Image Size with Minimal Quality Loss?

Discussion in 'Mac Basics and Help' started by rekhyt, Nov 20, 2010.

  1. rekhyt macrumors 65816

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    #1
    I have a few scanned in images of some some pages that I need to digitise. They're each roughly around 5.1MB with 600 DPI, but I can't really afford to have scans so large because I only have around 16GB to last for another 7 months.

    I want to decrease the image size but I need to have minimal quality loss of the image. Can this be done?
     
  2. Blue Velvet Moderator emeritus

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    #2
    What kind of pages are they? Mainly text or images as well? Why the archival resolution?

    If it's just B&W copy you could probably drop the resolution down to 450ppi and still keep the type sharp, convert them to greyscale and then save them as JPGs at anywhere between 9-12 quality... and they would be indistinguishable from the original scans when printed, with file sizes of probably about 20-30% of the masters.

    If they're colour pages, you could do the same. At 600ppi, you're scanning at half-tone levels of resolution which you may not need. It all comes down to what sort of material you have and the uses that you might put it to later.
     
  3. rekhyt thread starter macrumors 65816

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    #3
    Hello Blue Velvet,
    Thanks for your response. The scans are all colour. I'd like to keep file sizes down and retain quality of the colour image as I mentioned. (The size of the scan is A4, portrait.)

    I'd like the text to be readable because I intend importing the scans into Evernote for text recognition and searching.

    Would the 450DPI and the 9-12 JPEG quality method you mentioned be good for this purpose?
     
  4. Blue Velvet Moderator emeritus

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    #4

    I'm sure they'll be fine. 300ppi can be a bit lo-res for type when run out on a laser printer. If they're colour, then I'd stick to 10-12 for JPG quality. Best thing is to do a test first on one or two. Two questions first:

    1. What image editing software do you have?
    2. What format are your master files? TIFs?
     
  5. rekhyt thread starter macrumors 65816

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    #5
    1.
    • Adobe Illustrator CS5 (Vector program... Might count, might not.)
    • Adobe Photoshop CS5
    • iPhoto (2008)
    • Corel Painter Essentials 3 (Not really image editor)

    2. Format is JPEG.
     
  6. Blue Velvet Moderator emeritus

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    #6

    Then you have everything you need to do the job and when you've done a couple of tests to see what works, what you can get then down to, you can even set up a batch action to automate doing all of them in one fell swoop. :)
     
  7. rekhyt thread starter macrumors 65816

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    #7
    Thanks again for your replies. :)

    I have a few questions:
    • How do you automate batch actions in Photoshop?
    • How would I test to see if 'it works'? - Do I gauge it myself visually (To what extent?) or send it to Evernote to see if it'll recognise the text through the text-recognition system?
     
  8. Blue Velvet Moderator emeritus

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    #8
    Here you go. You have to set up an action first if you want to customise a batch process.

    Do both. Open up before and after files in Photoshop next to each other and eyeball them closely at 400%... and send one to Evernote. I can't decide for you what will be good enough to meet your requirements, because I haven't seen the files and I'm not entirely sure what will meet your goals.

    You say your master files are currently JPGs at 600ppi and that your main problem is file size. The question for you is how much you need to further compress them by to retain fidelity and reduce the file size to a set target or percentage in order to fit them into your storage solution.

    Personally, I'd burn the lot of them, as they currently are, onto a set of single layer archival DVDs if storage is a problem and you need to get them off your hard drive or whatever.
     

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