How can I set the Photoshop pencil tool to auto erase to transparent?
Photoshop's pencil tool has a setting for "auto erase". When set, clicking on a pixel of the current foreground color causes it to draw over it with the background color. This is great if you're drawing on a colored background, but useless when the background is transparent.
How can I set the pencil tool to erase pixels (replace them with transparent) instead of just drawing the background color over them? Or if this is not possible, is there another tool that can be set to draw a single pixel in the foreground color and then auto erase to transparent?
Looks like the Auto Erase works simply with the Foreground/Background color pairs, whenever a FG color is detected under the cursor, it switches the paint color to BG.
And Photoshop doesn't support alpha values for colors, so it seems that the only way to get rid of pixels is to use the Eraser tool itself.
I also looked if there was a keyboard modifier for the Pencil tool, that would make it an eraser while a keyboard button was pressed down, but found nothing for that either. I could've sworn I had used it before, it would have made a handy speedup for drawing, but it was probably some other program then. (Though I found out that dragging with Alt-RMB changes the brush size, which is handy!)
For anyone still interested in the solution to Robert's problem. Use the regular eraser, and change the 'Mode' from "Brush" to "Pencil", or "Block".