I often use ImageOptim and ImageAlpha to optimize images. ImageAlpha has a really nice feature because it lets you compare optimized image to the original one before saving it. Is there a software that does exclusively this (comparing two images) in a convenient way?

  • 1
    The first one that popped into my mind is Kaleidoscope. Not sure how it stacks up when compared to other image comparison apps though.
    – Joonas
    Nov 15, 2016 at 15:35
  • I didn't know this and it seems great. A bit expensive, though
    – Carlo
    Nov 15, 2016 at 18:54
  • 1
    What are you looking for in the app? I was thinking that if you select more than one image in finder and then use quicklook space bar, you can then view them side by side if you click that icon that is like 4 small squares. - How about PixCompare
    – Joonas
    Nov 16, 2016 at 0:18
  • I know about the quicklook trick, but that doesn't let you easily zoom in to precisely compare the details. PixCompare seems promising, I'll have a look into it
    – Carlo
    Nov 16, 2016 at 9:27
  • 1
    I put Image diff in the app store search and got these two: Pixel Diff, ImageDiff.
    – Joonas
    Nov 16, 2016 at 9:46

2 Answers 2


Not in any specific order.

  1. Kaleidoscope - $70 ( Mac )
  2. PixCompare - $4 ( Mac )
  3. Pixel Diff - $2 ( Mac )
  4. ImageDiff - $2 ( Mac )
  5. Araxis Merge - $150 give or take ( Mac and Windows )
  6. Image Comparer - $35 ( Windows )
  7. Image Diff Tool - Free ( Mac, Windows, Linux )
  8. Beyond Compare - $30 (Mac, Windows, Linux)
  9. Resemble.js Free ( Web application )
    • I was thinking that if you wanted to, you could pretty easily extend the functionality of this with a comparison jquery plugin or something, to extend what it can do, like this for instance.
  • the last link (Resemble.js) has moved to huddleeng.github.io/Resemble.js (I cannot update the comment as the edit is too "small" -- @Joonas if you could update it, that would be great!) Jun 29, 2018 at 1:26
  • @GregSadetsky updated the link.
    – Joonas
    Jun 29, 2018 at 11:19
  • on price point, Kaleidoscope definitely leads!
    – ina
    Apr 8, 2019 at 20:21

By "processed image" I assume you mean that the resolution/size/format/colors were changed for, say exporting to the web (rather than the color correction and retouching you might do with Photoshop).

GraphicConverter can do this with the Compare Images menu command. I haven't used this function much, but GC has an impressive array of tools for analyzing the image EXIF, histogram, etc. There's an extensive collection of manuals that come with the program and it's shareware, so worth a look..

Photoshop CC allows you to preview effects of exporting a processed image as a different format (say a jpeg with reduced quality). In older versions this was called "Save for Web" and you had the advantage of being able to compare results of up to four different resolutions. I'm not sure why they removed this feature, unless it was just moved somewhere else.

  • In Photoshop, use File > Export > Save For Web (Legacy) Nov 15, 2016 at 17:01
  • probably I wasn't clear enough in my question: I need a tool who lets me compare two images by putting them side by side, or one over the other. Kaleidoscope seems to do what I need, but is a bit pricey
    – Carlo
    Nov 15, 2016 at 18:54

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