How do I do a realistic color change on a realistic fractal map ?

[Deadshade]

I am still in the GIMP apprenticeship setting where I try to do per software what I do correctly per hand. I generally can't do as well with GIMP as per hand and sometimes I do outright worse.
But as I now know my GIMP to at least 60%, I think that I know where my biggest problem is.
It is in color transitions.

For instance there is a green forest that gradually thins out and goes over in a red/yellow desert.
I can do a correct forest and a correct desert but what I can't get is the correct transition.

Either there is a sharp green/yellow boundary that hits like a fist on an eye or a blurred zone that makes a color transition but destroys the fractal look of the map.
I also thought of making a color gradient layer superposed on a bump map which keeps the fractal features. It's almost what I want but the change is too regular.

What tool/technics should I use in GIMP to manage a color transition without destroying the fractal look ?

[johnvanvliet]

A fractal terrain generator should give you a Height map that is ?? 16 bit unsigned ( or Signed) integer 0 to 65536 , -23767 to +32768
or a 32 bit float



gimp handles 8 bit only for now ( 0 to 255)

the best tutorials will be for "colorizing old Black and White photos " or "colorizing Black and White images"
there are a TON and then some on the net
like:
http://tutorialgeek.blogspot.com/201...otos-from.html
http://www.digitalphotoguide.net/pos...te-photo-gimp/

there is ALSO a built in tool called "Sample colorize "
/color/map/sample colorize
this requires a b&w image to be colorized and a image to make the gradient from

Use layers and masks that is what i did on this old "blue" Mars

i also added in about 10% of a "emboss" of the height date for some shading

now that was a FAST created recoloring , done in part of one evening while half watching TV

[Deadshade]

Thanks much for the links.
But my problem is not how to color black and white images - that's easy. As soon as one does a selection, I know how to get color and/or texture in the selection. This is typically what I meant when I mentionned "superposing a bump map (e.g a black and white image) to a colored layer."
My problem is how to realize a transition between 2 regions of different colors so that this transition happens gradually with no obvious boundary.
For this task selections and masks don't work because they precisely lead to sharp boundaries.

For instance your Mars example nicely illustrates the problem I have.
One sees clearly green regions, blue regions and grey regions that have all very sharp boundaries and that's precisely what I would like to learn how to get rid of.
I put on the image arrows that show where the unwanted boundaries are.



What I would like to learn is how to do this :

[johnvanvliet]

use the air-brush tool to blend
i did very little of that

and some of those hard boundarys in the rendered image is the clouds

[Deadshade]

Air brush is great for blurring but once a color is chosen, it doesn't allow to make disappear the hard boundaries between colors. Or if it does, I didn't find how.
The Earth green->red example I have shown is impossible to do with air brush.

[Freodin]

You could try that...

... make a rough layout of the blending colours in black and white. If you want a smoother, but still clearly defined transition, add some grey in-between steps by hand.
... give it a generous gaussian blur.
... create a gradient with the colours you want to have shown. The most simple would be Foreground colour -> Background colour... but you can get as artistic as you like.
... use "Colour/Map/Gradient Map" to transfer your colour scheme to your black and white layout.

[johnvanvliet]

most if not almost all color blending is done with a air brush
real and using paint or virtual and in a image editor

that "red" is more a sand color

if you want it to blend into a dark green

set the rate at say ? 30% and the flow at ? say 10 %
use a 80 % solid on the brush it's self
( you do not want to over do it )

and after a few wispy passes
-- a "blotchy" blend like grassland

[Deadshade]

Thanks for the suggestions.
An image is better than 1000 words.
This is an extract of one of my maps - it shows a forest region transiting in a desert/Savannah towards NW.
The forests are OK both in texture and color. The desert is OK both in texture and color.
What is not OK at all is the ugly color boundary.
What I am looking for is whether it is possible to create a color transition so that this color boundary disappears but the textures are conserved.
Gradients don't help and a brush just adds more or less blurred blobs which destroy the texture.

Perhaps what I want to do is impossible - I am not GIMP expert enough to tell. Or perhaps I must do the transition by hand and add the desert only once it's done.

[Freodin]

If you use a colour overlay to colour the desert, instead of a coloured texture, you could do the following.
You should be able to use a layer mask to reduce the alpha of your colour overlay. That would gradually reduce the colour of the desert, and you could directly control where it fades, by adjusting the mask.
As the mask would only change the colour overlay, the texture would not be influenced.

[Deadshade]

Not sure I understand.
This is precisely how I created the desert - using a mask on a texture (B&W) layer so that the underlying yellow came through.
But of course as the mask has a sharp boundary, it created a sharp boundary with the forests too. And I don't know how to make it disappear.

Actually thanks to you, I thought about it deeper and I know now what I need - I need to create a diffusion pattern.
It's like an irregular band running along the boundary so that on one side the pixels are 100% yellow, around the middle the pixels are approximately 50% green and 50% yellow and on the other side they are 100% green. As the distribution is random, it conserves an irregular pattern.
The width of the band regulates the smoothness of the transition.
Now the question is whether GIMP or PS can create a kind of diffusion pattern.