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In this image I have to change red to grey:

enter image description here

I know I can just set the saturation to zero, but then the result is a grey that is to dark.

enter image description here

I could just change the brightness, but that would also change the left lower part of the picture:

enter image description here

Is there an adjustment that only works on the red parts of the image? I can't use a selection, because the setting has to be applied to lots of images.

EDIT

I tried to use "replace adjustment tool", but that did not work well for the shdows and bright parts of the image, even with the largest fuzzines. I used blue as the replacement colour, to have a better impression of what it does.

enter image description here

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Why not use the in-built Replace Color tool? –  Ƭᴇcʜιᴇ007 Aug 25 '12 at 19:49
    
I checked replace tool, but that did not work well for me. –  Malcolm Frexner Aug 26 '12 at 17:22
    
There is a related question on Graphic Design. You might find that useful. If it doesn't quite fit what you need, you can post a question there yourself. You will most likely find more experts on this topic over there. –  awe Aug 31 '12 at 10:47

4 Answers 4

up vote 4 down vote accepted
+100

You should check out the Black and White Tool (Ctrl+Alt+Shift+B). There you can set the saturation for each color channel individually:

enter image description here

Which got me this result:

enter image description here

In this screenshot the shadows still looks a bit too bright, but if you try it yourself and undo/redo you will see that the shadows don't change at all.

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This worked like a charm. I only had to set the red channel. –  Malcolm Frexner Sep 2 '12 at 19:10

Zoom in on the image in the area you want to replace the color. Using the select magic wand, click the in the area with the color you wish to replace. Shift-Click any area where the magic wand didnt pick up. Repeat until the entire area you want is selected. Then you can replace with another color.

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I cant use a selection because the setting has to be applied to lots of images. –  Malcolm Frexner Aug 28 '12 at 9:10
    
welcome to the world of graphic design. –  Keltari Aug 28 '12 at 9:20

You can do this with an action, and because it is an action, you can run it as a batch job on an entire folder.

(Note that I don't know if the terminology is the same in your language version of photoshop, I apologize.)

Open your image.

Create a new action. Begin recording

Choose "select color range", select a red pixel with the eyedropper, move the fuzziness slider all the way to 200. Hit ok.

hide your selection (ctrl+h) to make it easier to see what you are doing.

Using the hue/saturation tool (ctr+U) reduce saturation all the way to grey (-100) and boost lightness to maybe +15.

deselect (ctrl+d)

You'll notice a slight red halo around items. To eliminate this, convert the image to greyscale. You can then convert it back to rgb if you like.

stop recording the action.

make a temporary folder, put COPIES of all the images you need to run this action on.

start a batch job (file menu, automate, batch) choose your recorded Action, choose the folder with the temporary copies as source, and choose "save and close" as destination.

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You need to select the layer (assuming this is a single layer) and then from the layer palette, select the Channels tab. You can turn on / off each channel (with the eye symbol) until you see what you want to remove. I've done this before and it worked very well. If you need more instructions let me know.

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