I have an Epson scanner and i have scanned a photo to my mac book pro.

I am running macOS BigSur 11.6.7.

Finder is showing the size of the resulting .tiff file as 6.2mb. I wanted to select a portion of the photo and then create a new .tiff file from the selection.

Here is what I did

  1. I opened the scan photo in the preview app.
  2. I selected the portion of the image I wanted to create a new file out of.
  3. Copy the selected portion.
  4. Cmd N, this open a new tab which contains the copied portion of the image.
  5. I saved the new file with a different name.

The size of the new file is 30mb. Now, I was expecting the new file to have a size much smaller than the original.

What is happening? Why is the new file so big?

  • 2
    Perhaps the tiff file as created by the scanner is compressed, and the file Preview created from your selection is not. Post the output of file(1) for both of them. Commented Jun 21, 2022 at 21:30

1 Answer 1


TIFF images can either be compressed, or uncompressed. Uncompressed images will be number of pixels x bit-depth, so a 30Mb, 8-bit image is going to be around 5,500 pixels square. (A 16-bit 30 Mb image will have half the number of pixels, so c. 3,900 square).

By default, Preview will save without compression. When you Export the image from File > Export, there are options for the compression type, and you can see the effect on file size.

enter image description here

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