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Does an image in a, say, TIFF file have an explicit gamma or is it a latent characteristic of the image data ?

or to put it another way: can I tell what gamma correction has been applied to an image from the data in the image file ?

Some background follows:

I have some TIFF files generated by the VueScan image scanning application. This saves two TIFF files, one of which is (what it calls) raw. The raw file is said to be Gamma 1 and the other one Gamma 2.2.

(VueScan's raw is "raw scanner RGB" data - it isn't the same as camera raw)

When I view the files they do look different; the raw one is darker as would be expected with Gamma 1. However, the "levels" dialog in Gimp or Photoshop shows its centre slider level set to 1.0 for both images. I don't know where or if I can see the different gamma levels in each image.

I note that after changing the slider and re-opening the dialog the slider position is back at 1.0, so I presume the gamma correction is just done and forgotten about - so there is no record of what has been done. Would that be correct?

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No. Take a simple example: suppose you shoot a pic of a table with a lamp on it. Shoot the same scene a few times, changing nothing but the brightness of the lamp (use a dimmable bulb :-) ). How would you know after the fact which image's gamma was due to post-processing and which due to the contrast between bulb brightness and dark corners of the room?

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    \$\begingroup\$ I was more concerned with there being a record of any gamma correction performed during post-processing. But I drew the same conclusion - that there isn't. \$\endgroup\$
    – starfry
    Commented Jun 22, 2016 at 12:16
  • \$\begingroup\$ @starfry: PNG has a field to store this information. If you save an image from Gimp as a PNG, it will offer to save gamma info. What it saves isn't related to edits you performed with the levels dialog, though... it's whatever gamma it thinks you were viewing at while editing. \$\endgroup\$
    – junkyardsparkle
    Commented Jun 22, 2016 at 18:11

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