When saving JPG images with Pixelmator or Photoshop, I select a quality from the scale 1–100 that gives optimum file-size.
Later on, I sometimes take these images and crop them a little more (not always possible to find the originals), but when re-saving I can no longer know what quality I saved them with.*
Are there any Mac programs that will reveal the quality that the JPG was saved at?
* Perhaps this is not the right way of going about it, because it seems that, for example, if I’m already saving a file that was saved lossy at 59 quality previously, and then go ahead and I save it again (even at 59 or 99), it will loose even more quality? Correct?
Yes! You can do this from command line (using the Terminal app) with ImageMagick.
After you install ImageMagick, navigate to the directory where your picture is located and run the following command:
identify -verbose yourimage.jpg | grep -i quality
yourimage.jpg is the name of the image.
And you should get the value which indicates the image quality. 0 means the lowest quality and 100 means the highest.