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I'm trying to create a reference image for a greyscale drawing. In the original reference photo, the subject is wearing a brown jacket and grey pants which have pretty much the same brightness, and look the same (and rather dull) when I go to black and white.

I want to make the jacket darker when I go black and white. The jacket is the only red/brown coloured object in the photo, so I thought I could do some sort of level adjustment to make the brown jacket darker before going black and white. But I'm not so sure how to do this.

I'm using GIMP. I don't have access to photoshop.

Here is the problem:

Colour

Very different colours

Black and White

This difference is lost on going to black and white

  • Can the downvoter please tell me why they downvoted, so that I can make my question better? – fhyve Apr 5 '15 at 6:55
  • Not sure "general" levels help applies. All applications operate differently. In addition, I am also uncertain this can be accomplished "without selecting the jacket" since any "general" adjustment is also going to alter the trousers without a selection. I think you're asking for a method which requires little or no effort, and often, those don't exist. – Scott Apr 5 '15 at 7:21
  • But in principle we can distinguish between the two colours, so we should be able to exploit that difference. Like, in this case we want to transform the difference difference between red and cyan to a decrease in brightness. Something like (R,G,B)_new = (R,G,B)_old + (x,x,x)*((B + G)/2 - R) with an adjustable parameter x. – fhyve Apr 5 '15 at 7:34
  • There are two reasons I don't want to use the select tool. First, I'm on a laptop with a trackpad and I will be inaccurate. Second, the edges of my selection will be sensitive to shadows, so if my selection is messy, there is a good chance that I will add in false shadows and highlights along the edge of the jacket. – fhyve Apr 5 '15 at 7:58
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    The blue component of the sample image (obtainable by e.g. a Decompose to RGB) has the most noticeable difference for those two colors. If this works out for the rest of the whole image, you could cheat and just use that as reference image. – Michael Schumacher Apr 5 '15 at 18:56
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I don't know how gimp work, but talking about the concept. The two color seems to have the same average gray so when you convert it to grayscale it doesn't make any difference. all you need to do is some color equalizing before conversion.

try to work on the colored version first, by equalizing the color and raise the blue a little this will ensure raising the black over the jacket more that the pant.

this is the result I reached by using the "Blue High-Contract"

enter image description here

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