steven_woody Posted November 16, 2007 Share Posted November 16, 2007 hi, in PS, does the gamma correcting mean play with the middle slider in the level tool? if i have a linear tiff file without gamma correcting ( maybe i should say the gamma is 1 ) and want to correct it to a gamma value of 2.5, what should i do in the level tool? thanks. - woody Link to comment Share on other sites More sharing options...
colinsouthern Posted November 16, 2007 Share Posted November 16, 2007 Image -> Adjustments -> Exposure. Link to comment Share on other sites More sharing options...
steven_woody Posted November 16, 2007 Author Share Posted November 16, 2007 thanks. but what exact value should i apply? 1/2.5 = 0.4? and, i also noticed the Image->Adjustments-Exposure->Gamma seems identical to the middle slide in the Level diagram, except the value inversed. am i right? Link to comment Share on other sites More sharing options...
teeuwen Posted November 16, 2007 Share Posted November 16, 2007 The behavior of the middle slider in the levels dialog is inversed. To apply 'gamma encoding/correction' to a linear file you should use the inverse of gamma 2.2 being 1/2.2=0.45. As the scale in levels dialog is inversed you should use 2.2 Link to comment Share on other sites More sharing options...
digitaldog Posted November 16, 2007 Share Posted November 16, 2007 That slider in Levels may be called a gamma slider but that's not what it's doing (it doesn't follow the gamma formula). I also don't know why you'd want to apply some arbitrary gamma value on a linear encoded image. Apply a tone curve that makes the image appears as you want it to (unless you're doing some science). Author “Color Management for Photographers" & "Photoshop CC Color Management" (pluralsight.com) Link to comment Share on other sites More sharing options...
teeuwen Posted November 16, 2007 Share Posted November 16, 2007 > but that's not what it's doing (it doesn't follow the gamma formula). See "Note on Photoshop Gamma" on pages 18 and 19 of David Dunthorn's "Maintaining Color Integrity in Digital Photography": http://www.c-f-systems.com/Docs/ColorIntegrityCFS-243.pdf Link to comment Share on other sites More sharing options...
bernardwest Posted November 17, 2007 Share Posted November 17, 2007 My understanding of it is this (hopefully Andrew can correct me if and where I am wrong): The gamma correction is normally applied before white balance adjustment is applied in the raw conversion. If you try and apply the gamma yourself to a linear raw converted file it will be different as when done by the raw converter, as one or more channels may clip in the white balance correction. Also, the destination colour space will determine how the gamma is applied. For RGB it isn't a true gamma curve. There is some extra voodoo going on in parts of the curve (particularly shadows I think). Link to comment Share on other sites More sharing options...
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