0

When I use Image Capture to scan a 4x6 print photo on my flatbed scanner at 600 dpi, with no rotation applied to the bounding box, the resulting TIFF file is generally around 11 MB in size, and the same scan saved as JPEG is about 1.2 MB in size. However, I've discovered that if I use any nonzero amount of rotation on the bounding box, the resulting TIFF is about 1.8 MB in size, while the same scan saved as a JPEG is (again) 1.2 MB in size. In other words, I'm consistently finding that applying rotation shrinks the file size of the resulting TIFF by a whopping 85% — nearly as big a difference as saving in JPEG. Other than the tilt, however slight, the two TIFFs are visually indistinguishable, and both have exactly the same dimensions in pixels. If I open each TIFF in GraphicConverter 12 and re-save each as a TIFF with ZIP compression, both of the resulting files are about the same size as the original zero-rotation TIFF (i.e., the shrinkage of the rotated-capture TIFF goes away).

Here's a small screenshot to illustrate the results of my test:

Image-scan test results, zero vs. nonzero rotation

Again, I have found this result to be consistent across dozens of scans. What on earth is going on here, to make the very-slightly-rotated-capture TIFF so dramatically smaller than the orthogonal-capture TIFF?

Improve this question
1
  • You might increase your chances of gettinga good answer if you share the TIFF and the rotated TIFF using Dropbox, Google Drive or some service that doesn't alter images. Commented Jul 9, 2025 at 9:12

1 Answer 1

Reset to default
1

This question from 2020 suggests the answer: Image Capture uses lossy JPEG compression inside TIFFs captured with a rotated bounding box, but lossless LZW compression if captured with an orthogonal bounding box. I find this utterly bizarre and inexplicable, but there it is.

I suppose that if one wished to save a rotated scan with lossless compression, one would have to save it in PNG format.

Improve this answer
1
  • I suppose a follow-up question would be: Since the rotated-capture TIFF uses JPEG compression, why is the resulting file about 50% larger than the same scan saved directly to JPEG? I would expect any extra overhead from the TIFF format to be much less than half a megabyte, so… are different JPEG compression parameters being used in each case? The whole situation is quite strange. Commented Jan 15, 2025 at 17:16

You must log in to answer this question.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.