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Merging/fading images together & other things

Jul 13, 2011, 11:13
Post: #1
Merging/fading images together & other things
Hi,

I'm wondering if someone would be able to help me. I've been playing around with Gimp and making some wallpapers and stuff recently. I'd really like to know how to do something like this: http://img834.imageshack.us/img834/5479/...366768.jpg

It's really hard to explain what exactly I want to know, but I'd like to make something similar with a collage of smaller pictures that all sort of merge into each other like they do in the example. Questions:

- How do I get the backgrounds (of the whole thing, and each separate image) to just fade out/into each other so seamlessly?
- Is there a way to make a layer transparent in some parts but not in others?

Hopefully someone will be able to help me a bit! Thanks in advance to anyone who does. Smile
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Jul 13, 2011, 12:36
Post: #2
RE: Merging/fading images together & other things
Basically:
  • each picture added to the image is a layer.
  • a layer can have transparent parts (the "Eraser" tool only makes the layer transparent where you "rub" it, for instance).
  • actually every pixel of a layer can take all degrees (256, actually) of transparency, from fully opaque to fully transparent.
  • Besides the 3 colors (RGB) a fourth channel (the "alpha channel") holds the opacity value of the pixel. In other words, the opacity of any layer is controlled by a grayscale image, where black is fully transparent and white is fully opaque.
  • you can edit this grayscale image using a "Layer mask".
So for instance, if you start from this:
[attachment=531]
And add an alpha channel like this:
[attachment=532]
You get this (special background added for better visibility):
[attachment=533]

Any method to draw images can be used to obtain the layer mask. Here I used a radial gradient+"Levels". Repeat the process for each part of the picture. You can furthermore adjust the overall opacity of each layer.

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Jul 13, 2011, 22:08
Post: #3
RE: Merging/fading images together & other things
Since we are talking about images. I am trying to color the background behind the image, but it keeps filling in the entire thing. Thanks!
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Jul 13, 2011, 22:59 (This post was last modified: Jul 13, 2011 23:00 by ofnuts.)
Post: #4
RE: Merging/fading images together & other things
The best way to color a background is to have a transparent background in the "subject" layer, and add a layer below and color it fully. You don't care what the pixels in the background layer are where the subject layer is opaque, and partial transparency in the subject layer converts to a nice blend between subject and background:

[attachment=539]

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Jul 13, 2011, 23:43
Post: #5
RE: Merging/fading images together & other things
Hi,

thanks for your reply! Can you tell me how I actually make the alpha channel you've pictured? I played around with the radial gradient thing in a circle selection but it didn't fade as nicely as yours did. Step by step? *is hopeless*
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Jul 14, 2011, 00:34
Post: #6
RE: Merging/fading images together & other things
Assume you want a pure white circle with a 100px radius, everything beyond 200px to be full black, and a gradient between the two:

- fill layer with black
- create a circular selection with a 150px radius (ie, about half way)
- fill selection with white
- Filter/Blur/Gaussian with a 50px (ie, half the gradient again).

It can also be done with gradients and the Curves dialog to more accurately control the gradient, but this will be for tomorrow.

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Jul 14, 2011, 01:37
Post: #7
RE: Merging/fading images together & other things
Cool, and you could do that with any shape too, couldn't you? Awesome/ Thanks heaps for your help!
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Jul 14, 2011, 11:47
Post: #8
RE: Merging/fading images together & other things
Any shape for what?

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Jul 14, 2011, 12:25
Post: #9
RE: Merging/fading images together & other things
As in, it doesn't have to be a circle with a blur around it? Well, maybe it sounds better in theory than in practise.
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Jul 14, 2011, 12:51
Post: #10
RE: Merging/fading images together & other things
If you have a free shape, you can use a "dimpled" gradient but the gradient is inside the selection. If you want a fading gradient of a given widths that starts around a selection instead of inside like the dimpled gradient, then there is my Wrapmap plugin: http://gimp-wrapmap.sourceforge.net/

For instance, after a selection on the head contour, apply a 50px gradient in the layer mask around the contour, so the head remains completely sharp (see attachment).

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