Some Photoshop + Alpha channel tips from someone that's been using the app for 10+ years.
1) Magic Wand tool is your best friend when isolating irregular shaped images. The tollerance setting controlls how many color shades neighboring pixels can differ from the pixel you click and still be grabbed in the sellection. The Anti-alias setting will allow the tool to smooth out the jaggies by partially sellecting edge pixels that don't fall inside the tolerance but do form a corner bettween 2 pixels that are in tollerance.
2) You can copy/paste to and from Alpha channels. Pasting a color image to an alpha will convert it to Grayscale.
3) While still in RGB mode, you can click the Eye icon for the Alpha Channel in the layers pallet to show the Alpha as a semi-transparent visible color. Use Layer Option from the pallet menu to pick whatever color is easiest for you to edit with, it has no effect on your DDS output.
4) A really fast way to make complex alphas is to duplicate one of the color channels, use the Levels command (Ctrl + L) to adjust the light and dark threasholds, then fill in with Airbrush and Pencil as needed.
5) You can load any alpha channel as a selection with gray values loading as opacity values.
6) The right button at the bottom of the tool pallet (gray square/white circle) switches you to "Quick Mask" mode where you can edit your current selection as a paint layer.
7) Really complex alpha building is often best done in stages. Use 1 method to select some stuff then save the selection. Use another method to select something else, switch to the alpha you saved, then delete to white or black.
Using the dragon book as an example. If I were to build that alpha from scratch using just the color image, I'd first MagicWand the background (tolerance 20) and save that as alpha.
To issolate the wing membrain I'd dupe the Red channel (it has good contrast), then Levels it to make everything nearly black except the wing membrains. Load the alpha as a selection and choose inveres selection. From the Select menu choose Modify/Expand 1 pixel to grab the stray edge pixels. Delete the background to black. Now use the rectangle selection to fill in whatever gray isn't part of the membrain.
To merge the 2, switch to your alpha channel. Load Red Copy as a selection and Delete to, or fill with white. If the membrain isn't opaque enough, detlete/fill again. Use Fill with opacitcy controls if you want finer control of the fill amount.
Tip: Alt + Del fills with the forground color.
|