: Replicate curves adjustment in Photoshop I edited an image with a curves adjustment on all the channels (RGB, red, green and blue). Now I want to know how those curves looked like, so I can

@Kimberly620

Yes you can do this. However it really depends on many factors. First of you can just simply use some scientific plotting tool to plot each value in 2D where x is original value and y is new pictures value.

I am using mathematica for this, quick and dirty mathematica code looks as follows (but you could choose any other tool):

src = ColorSeparate[Import["c:temptest.png"]];
srcAdj = ColorSeparate[Import["c:temptestadj.png"]];
r = Flatten[ImageData [src[[1]]]];
r2 = Flatten[ImageData [srcAdj[[1]]]];
rtp = Transpose[{r, r2}];
g = Flatten[ImageData [src[[2]]]];
g2 = Flatten[ImageData [srcAdj[[2]]]];
gtp = Transpose[{g, g2}];
b = Flatten[ImageData [src[[3]]]];
b2 = Flatten[ImageData [srcAdj[[3]]]];
btp = Transpose[{b, b2}];
Show[ListPlot[rtp, AspectRatio -> 1, PlotStyle -> Red],
ListPlot[gtp, AspectRatio -> 1, PlotStyle -> Green],
ListPlot[btp, AspectRatio -> 1, PlotStyle -> Blue]]


So for test ive used following curves as the adjusted image (image used):



And mathematica gives me:



Which is pretty close, or possibly exactly the same value. Making a curves adjustment file out of this wouldn't be too hard*. However a word of warning! If your images are lossy, like jpeg compressed, then this will not work. Example with jpegs:



Now the plot points are all over the place and youd have to try to filter the data somehow. So the take here is that if the image has something other than just a curves adjustment then the thing just blows up.

* If the data was read in with the code above then the curves export is:

file = FileNameJoin[{ "C:temp", "out.amp"}];
BinaryWrite[
file, (SortBy[DeleteDuplicates[rtp], First] // Transpose //
Last) *255 // IntegerPart];
BinaryWrite[
file, (SortBy[DeleteDuplicates[gtp], First] // Transpose //
Last) *255 // IntegerPart];
BinaryWrite[
file, (SortBy[DeleteDuplicates[btp], First] // Transpose //
Last) *255 // IntegerPart];
Close[file];


the amp file can then be read to a photoshop curves layer for example. And it produces same image in my test case. The code is not really performace oriented but it works.

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@Nimeshi706

If you'd have used a single curve per channel, and you have your input and output images, you could derive the curves back using some image processing.

But since you used both the RGB curve and the individual R, G and B curves, that is (I think) impossible (or exceedingly hard), since you won't be able to tell how much the RGB curve or the individual curves each contributed to the output.

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