why would you simple flatten an image??
Are you asking about coloring 'flats' or flattening layers?
Don't forget that Photoshop is used for waaay more than computer coloring comic book drawings, so features like channels and paths may not have an immediate use for what you're doing, but they do have other uses.
colorin flats...
this is the flattenin im doin for a quick firebrani comic...
http://tartarsause.deviantart.com/ar...andi-111466472
but why make simple colors for different parts of an image instead of selecting and coloring them on the spot??
One excellent reason for putting in all your flat colors first is that colors can look different compared to other colors. So if you just go through and detail color your project bit by tiny bit, it might look weird at the end because you never saw how all your colors interacted before going straight through.
And as stated before, channels have a lot of correction usage. Photoshop does a HECK of a lot of stuff and kind of just happens to be nice for digital coloring too.
I don't use Photoshop, I use Paintshop Pro (8)(the pre-corel version, since the post-corel versions suck) and have only just started using layers for my work.
Color flats are useful in some cases, but I think it depends on what you want to do with the piece. Some folks color and shade each figure in a complex scene separately, while others do flats whole and then go in to shade the whole thing... Everyone does it differently.
When color-matching is important, say in a comic which has panels, and not just a single piece of art, flats are something that should be in use by everyone ever. Make sure you have the right colors *before* shading, instead of realizing halfway through your page "omg that guy's arm bracer was supposed to be RED not GOLD!"
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Often what people will do is set up a 'palette' layer, with splotches of the colors they will be using - then when you're coloring your flats you can use the color picker to select the same colors each and every time.
Then you simply delete or hide the palette layer when you're done.
Another reason to do layers in flats is, you may want to change the background, or adjust the skin tones, without globally altering everything else. If you have channels/layers for these things, you can change them or re-color them independently of the other parts of the image. Then merge layers when you're satisfied with the flats stage, and create new ones for highlights and shadows and such (if you need to free up memory).
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One of the great uses of flats, is that you can make an instant selection of the area, rather than lasso it all again and then start coloring. If you keep a new layer of all flats, and uncheck the eye on the side of that layer, you won't see the flats, but they will be there if you miscolor something, or have to start over, cause as you work you may want to change things.
Let's say I have colored the entire face AND the hair, but all on the same layer. If I need to change the hair color, I run the risk of messing up the face, unless, I lasso the hair, and work on a new layer. It's not always "safe" to keep an area in selection, as sometimes your hand might hit the wrong key and you could lose it and then have to do it over again.
However if you have the area flatted on the flat layer, you can select that with your magic wand, go back to the layer you first colored on and either change it there with color balance, or saturation... or save it on a new layer and start again.
A flat layer is basically a safety net. You can work without it, but unless you never make a mistake, you're playing with fire work wise. Chances are you will wish you had it, if you didn't make one.
photoshop coloring question..
...supposin that flatten would be making all the different aspects of a drawing in simple colors so there easily selectable for coloring..
but.. well if your right there and its selected.. shouldnt you just color it ?
..and while im at it... what good is the channels and path areas for anything????