WARNING: MATH AND PHYSICS
many of us see the channels tab as a nice way to turn scanned line art into a transparent layer, but how does it work?
"we’re paying $39.99 a month for four channels what a ripoff"
the channels record how much of each color (red, green and blue, if you are in RGB mode) is in your image! the way to think of the channels (and, in the end, what they really are) is that they are additive layers of red, green and blue.
"additive?" you say. "what does that mean?" well, if you add red to green to blue, they make white (at least, when you are mixing light and not paint!). the white parts of your drawing are a result of green, blue and red being added to each other. the other colors of your drawing are a result of the different colors being added in different amounts to each other. if you add green to blue, they make cyan. if you add blue to red, you make magenta.
therefore, if you subtract red, green and blue from white, it should make black, right?
i will demonstrate on photoshop.
take white (ffffff)
add a red (ff0000) layer above it, and set it to “subtract”
you have now subtracted red (ff0000) from white (ffffff), to make cyan (00ffff)
now add a green (00ff00) layer above that, and also set it to “subtract”
you have now subtracted green (00ff00) from cyan (00ffff) to make blue (0000ff)
now add a blue (0000ff) layer above that, and set it to subtract
you have now subtracted blue (0000ff) from blue (0000ff), to make black (000000).(1)
what application does this have with your art?
well, you will notice at the bottom of the channels tab that there is an option to load the channels as a selection. because the selection tool is actually a very binary tool, it only thinks of things in terms of white and black (or: presence and absence. either something is there, or it’s partially there, or it’s not there at all). if you select only the red channel (on a red canvas), the selection tool will think of the red as “partially white”. so, when you choose the option “load as selection”, it selects all of the white and partially white (also known as “colors”), but none of the black. it thinks of the white areas as “opaque”, the colored areas as “translucent” and the black areas as “transparent”. what was once red will be gray, or a translucent white.
this is why this is so useful for doing line art! when you right-click your new selection and choose the option “select inverse” (or, another way to put it, “invert selection”), you now have all the black and partially black (or, partially not-white)(2) selected, and you can now fill them in with real black! you now have solid lines to work with!
(1) i suppose you may have picked up on the math of this. “f” is the highest “digit” in the hex color code (with a base of sixteen, each “digit” being 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, and f. a through f are stand-ins for what would be single-character numbers if our math was base-16. but instead, it is base-10. so we have 10 single-character digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. double digits would start at 16 instead of 10, and triple digits would start at 256 instead of 100. because we do not have a base-16 counting system, we substitute letters because they have single characters, and the hex codes ARE base-16.) so, f minus f is zero, like, say, 6 minus 6 is zero. you could think of “f” as 15. (sixteen, in this weird alphanumeric counting system, would be written “10”. seriously. 26 would be “1a”. 13 would be “d”.) furthermore, each two digits of the hex color code represent the amount of red, green and blue a particular color has. with this being a base-16 system and our numbers meaning slightly different things from normal, something like “80” would actually mean 128, because instead of representing 8 times ten, “80” would represent 8 times 16. “ff” is 255. there are 255 levels of red something can be, with “00” representing no red at all (so there are 256 levels in total for each two digits of the hex code, “00” representing a lack of color). “00ff00” means “zero red, 255 green, zero blue”. 00ff00, if you may recall, is green. 0000ff is blue. ff0000 is red. ffffff indicates a full presence of red, green and blue, and is therefore white. 000000 indicates a complete lack of any of these colors, and is therefore black. now you know (maybe) what hex codes mean!!!!!!
(2) you can think of white and black the way that hot and cold are thought of. white is a presence of all (visible) light, and black is an absence of any (visible) light at all. similarly, “hot” is a presence of heat and “cold” is an absence of heat. you can’t actually measure things in terms of how cold they are, but in terms of how “not hot” they are. a complete absence of heat would be zero kelvin, or “absolute zero”. black is kinda like that.
that’s not a dumb question! there are a couple of ways to do it, but i’ll show you the two that i usually use
the method i use most often is to take my line layer
and lock the transparency, as such:
all you need to do after that is just take the paintbrush (or your tool of choice) and draw over the area you want the color in. because the transparency of the layer is locked, the color can only go on the opaque parts of the layer, which in this case is my line art.
TIME OUT!!!! the drawing you linked me to as an example (http://dredsina.tumblr.com/post/39772819254) started as a pencil drawing that i scanned. if i were to attempt the previous technique with my scanned drawing, it would turn out like this:
because there is no transparency in my scanned layer! it is a solid image. the technique wouldn’t work. to make it work, i would need to turn my scanned layer into a transparent line art layer, which is what i did for this particular drawing. how to do this is to go to your “channels” tab:
click “load channel as selection”
then, making sure the tool you are using is a selection tool (marquee, lasso, or magic wand), right-click the work area and click “select inverse” (if you are not using a selection tool, this particular menu will not show up when you right-click)
now create a new layer!
then, using the paint bucket tool, fill the area with black (or whatever color you want the lines to be). make sure your paint bucket options are as such:
you now have a layer where everything “white” is actually transparent — an isolated line art layer!! cool!
there’s another option i use occasionally, though this is actually a technique i usually use for flat colors.
how it goes is that i make a new layer above my line art layer
draw the color i want in the area i want it to be
right-click the color layer and select “create clipping mask”
and that will make it so the contents of the selected layer will only affect the opaque (and translucent) elements of the layer below it.
et voilà! sorry this post was so long, but i hope it helped!