Step 2: Making the Sketch Blue

Okay, time to start mangling the sketch! First, go into your Image > Mode submenu, and make sure that "RGB Color" is selected. RGB stands for Red, Green, and Blue. Computers, televisions, and other such devices define colors in light, and can make any color by starting with a black screen and projecting amounts of red, green, and blue light to make colors. You'll notice there are some other modes here too, but for now stay in RGB color mode.

Levels Editor Go into the menus to Image > Adjust > Levels. This should bring up the Levels editor. The "Channel" selector indicates weather the levels you're looking at and editing is one of the three base colors (Red, Green, or Blue), or all colors together (RGB, the default). It keeps separate level settings for each of these four channels. The interesting-looking graph below that depicts how common the shades of the selected channel are, ranging from none (dark) on the left, to full (light) on the right. Since a sketch is white paper with some gray marks, the graph should show the levels clumped up towards the right, as in the screenshot here. If your scanner scans paper as light gray and not true white, the clump will not be up against the very edge like it is here.

The main control in this panel are the three arrows under the graph (the input arrows), and the two arrows under the gradient below them (the output arrows). Play around with these arrows to get a feel for what they do. The input arrows define where on the grayscale black, white, and true gray lie, and the output arrows define how white the brightest white can be, and how dark the darkest dark can be. A good example of their usefulness is if you do have a scanner that sees paper as light gray, you can move the rightmost input arrow just to the left of the large clump on the graph. This will tell Photoshop that you want to lighten the image so that the bulk of the image (the paper) will be true white.

If you have changed the levels in a way you're not happy with, hit "cancel" and then get the levels editor back up again. We're going to use the levels editor to turn the sketch a light blue. I do this because the gray of pencil can obscure some of the details of the black ink, and dark smudges cannot slip by as easy if they don't blend in with the sketch color.

Blue lines Here's how to make it blue: First, go to the "Channel" selector and select Blue. You'll want to make it so that blue is all light, so grab the dark output arrow (the one on the left) and drag it as far to the right as it will go. The gray lines on your sketch should turn a deep blue. This happened because there is now as much blue light in the dark lines as there is in the light paper.

Now select the Green chanel and drag its dark output arrow about halfway up. The blue lines should turn even lighter, and start to look sort of like they were drawn with a non-photo-blue pencil. If it's still too dark for your taste, you can drag it farther up, and even drag the red dark output up some. It should look something like the image to the left. There are other ways, even easier ways, to get the sketch blue, but it will help a lot if you familiarize yourself with the Levels editor, which can be very useful at other steps in the process, or even to do things like brighten up a final picture that is too dark.