THIS ONE is in 1024x1024, but unfortunately, if you want to use it, you need to add the black masking yourself. Use your good sense I suppose.Daybreak Nebula
The process is fairly simple:step 1: Black background
step 2: Create a new layer
step 3a: White swatch on new layer using paint tool of choice
step 3b: Small swatches for small clouds, big swatches for big clouds
step 4: Generate difference clouds on top of white swatch (ctrl+f is helpful)
step 5: Adjust blending modes and levels until satisfied.
step 6: Merge layers with background.
step 7: Repeat until you've got a big, satisfying cloud.
step 8: Post work. (step back, take a fresh look at your picture, and add any necessary clouds, smudges, paints, and whatever)
You should always step back from your work on a regular basis to make sure it's all coming together. If it's not, you can catch it before it gets out of control. If it is, you can start look for promising parts of the picture and develop them better than if you didn't use peripheral vision.
After you're finished, the painting should be merged into one layer, and it should still be B&W, otherwise desaturate it. You will save a lot of trouble by not coloring it yet.
Optional stepsstep 9: Use broad smudge and paint tools to sculpt clouds, lights, phenomena and shapes.
step 10: Use narrow smudge and paint tools to further define cloud edges for detailed effects.
step 11: color it (everything should have been B&W up to this point)
If you know how to use Difference Clouds
, Nebulae are a cinch. At any point you can also use the background eraser tool to tweak clouds and erase out black and white masks, but blending the layers into the black background usually takes care of this more expediently. The smudge and gradient tools are great for getting wispy effects, and the eraser is actually a really good for painting in reverse (as long as you don't use it on the background). It's not unusual to have blended some 50 difference clouds together to get one painting, and to have tweaked many of those to personally fit your tastes.
Coloring involves FIRST either applying a gradient effect to the white spots (you need to merge all layers and erase all black areas with the background eraser first) or by colorizing the whole image with the hue/saturation tool.
Coloring specific parts involves feathering the lasso tool and selecting a spots (I use between 10-40 pixels and the shift key to select multiple spots) All you have to do is use colorize, adjust contrasts, and adjust levels of the spot until satisfied.
You can also paint your own colors by creating a new layer, setting the blend mode to overlay (or hard light, or multiply or whatever) and painting with normal paint, gradient and smudge tools. You need a black background for this second approach.
I'm pretty sure that's all there is to it. If I think of something else, I'll say so.