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Hand coloring desaturated image help

Apr 5, 2013, 15:59
Post: #1
Hand coloring desaturated image help
Ok. Tired of beating my head against the wall. I have gone through a number of tutorials over the past couple of weeks and have mixed and matched some of the methods from those tutorials to create a composite image of a fictional planet. The tutorials has me desaturate the source images and then clone various pieces to my main image. I then went looking for better methods of adding color back to the image. Colorize produces some really nasty results, so I have been trying to do selective colorization.
The best results I saw had one using a brush and the "hue" mode. Setting it to color mode did work, but it doesn't look very good, the "hue" method looked best for what I am attempting to preserve in my image. However, I set up the brush and selected my color, went to brush in and nothing. The "hue" setting does nothing at all. I am confused to say the least. Changing the brush to color mode works, but "hue" does not. What am I missing? And yes, I am on the main texture layer and it is visible.
Other methods tried really are just variations of transparency with a solid or mixed color background beneath. I tried the fuzzy select tool, but hitting bucket fill did nothing. I am really confused. It is especially frustrating when one cannot follow a simple video tutorial and you can see you have the same settings and it is working for them.
If anyone has a solution, or even a better method entirely I would sure appreciate some advice. Please note: not an artist really. The difference between hue and color and saturation well... yeah somewhat lost on me.
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Apr 5, 2013, 18:20
Post: #2
RE: Hand coloring desaturated image help
So I have continued messing with it to try and figure out what is happening. Anytime I do something that pulls the color out of an image, desaturate being the most used by myself, the hue tool stops working. Now I am getting even more confused. The hue tool may be able to solve the problem, but I would not be able to work with B&W images to make the composite in the first place? That will make it difficult to match brightness between different images.

I notice their has been some views. Am I being a complete idiot or are others stumped as well?
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Apr 5, 2013, 21:16 (This post was last modified: Apr 5, 2013 23:47 by ofnuts.)
Post: #3
RE: Hand coloring desaturated image help
About the views, there are plenty of people that lurk and never post...

About your problem... You have to understand the "Hue/Saturation/Value" color model. In this model, the colors are described ith three values:
  • the Hue, often in degrees, with 0°=red, then orange, yellow, green ,cyan at 180°, blue, purple, and red again at 360°.
  • the Saturation (how much the color is visible)
  • the Value (the lightness), which is more or less the B&W version of the image
The color selectors in Gimp display both HSV and RGB values... you can also use the Pointer tool to display the HSV values of the pixels.

The difference between the RGB and the HSV model is that while the three RGB components are "added" for the final image, what happens in the HSV model is more like a multiplication. If the Saturation is 0 you get gray whatever the Hue, and if the Value is 0 you get black whatever the Saturation and Hue.

In "Hue"/"Saturation"/"Value" modes, the painted pixels have only their corresponding value replaced by the one from the brush color.

On a colored image the Hue mode works quite well. Find a picture of car with shadows and reflections. The shadows are areas with (mostly) a lower value, and reflections with (mostly) a lower saturation. Applying a new hue keeps the shadows and the reflections... But since you are working on a desaturated image (all pixels have S=0), "Hue" mode doesn't work, because without saturation all colors give gray. By contrast, "Color" mode transfers Hue and Saturation, and therefore can apply color to a desaturated image.

Btw, instead of using brush modes, use the brush in "normal" mode on a layer that you put in "Color" mode. This makes it easier to tune the coloring by changing the opacity of the layer. Layer modes and brush modes are essentially the same thing, and are described here.

To change the colors of things, I find that "Color/Components/Rotate colors" is often very efficient and quick. And to put back color in desaturated image, I often use "Color/Map/Gradient map".

[Image: 2Tvo0.png]

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Apr 5, 2013, 23:11
Post: #4
RE: Hand coloring desaturated image help
Thanks you! Bookmarked. I had somewhat figured that out, figured the "hue" tool was trying to adjust something that I had zeroed the value of. I will be trying the other tips regarding coloring the image.
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