I can't find good step-by-step documentation for creating the right kind of images. Presumably the gimp is a part of this, for lack of a decent tool. Well, here's a start, gripes included. Some things I've stumbled across while suffering:
You need to start with a good image. You want it big, generally a side view, and free to use. Don't worry about minor obstructions like wires; they can be removed with the clone tool and smudge tool. One might as well start with this. The clone tool is useless until you do control-click to start it. This would also be a good time to remove color casts with the curves tool. Use the jpegtran program if you will be making a greyscale stamp from a color JPEG, since it preserves data better than the GIMP. Ideally, one would do rotation last. This does not work well though, because a gimp bug will destory parts of an RGBA image. (learned the painful way) Gimp has three notions of what we might call alpha. 1. the selection, which is a hidden 8-bit channel (not a binary channel). 2. the layer mask 3. the alpha channel No reason is given for why the layer mask and alpha channel both exist. You can have both. You can, very awkwardly, convert one into the other. Many operations will only work on one. You can also convert either of these to or from the selection. Then there's quickmask mode, enabled by a button on the lower left of an image. It lets you paint the selection as a red haze over the image. Woe to you if your image looks like a red haze. Since the selection can be (awkwardly) converted to an alpha channel or layer mask, quickmask mode can be used to rough out the needed alpha channel. The basic problem when dealing with alpha is that you can't see it. The GIMP does not provide a good way to handle this problem. Ideally, one could drag-and-drop arbitrary channels and layers and images all over into each other, and could have many differently composited views all with mouse pointers and simultaneous updates. One can toggle layer visibility to flip between a layer with the image and one with the future alpha channel. With an actual alpha channel, you can't do anything. With the data as a layer mask, you can use an awkward and error-prone feature to choose what you see and what you draw on: use control-click and shift-click on the layer mask and/or layer (two side-by-side icons in the layers dialog) to muck with this. You can thus draw on the image while seeing the alpha channel, or draw on the alpha channel while seeing the image. Most likely you will, unintentionally and repeatedly. Away from your stamp object, you have some dead space on the drawing canvas. Fill this with a solid color to get better compression. Near the edge of your stamp object you will need to do some tedious pixel-by-pixel painting. Most image sources have JPEG artifacts that mess up the border. You'll need to color over these. Use the color picker and pencil, or use the clone tool. Extend the border of the image outward by many pixels to ensure that undesired colors don't leak into the image later as it is scaled, rotated, and so on. Be careful to ensure that the solid colors of your alpha channel (layer mask, whatever) and background are really solid colors. To do this, first select the region by color. Then, invert the selection. Now zoom in at least 4x and look for the moving selection ants. Color over them with the pencil tool set to full opacity. Redo the selection to check if you are done. When saving the image, be sure that you do not have a floating layer. (a cut-and-paste result for example) A gimp bug will mess up the output file if you forget. Avoid rotation entirely if you can. The GIMP operates without concern for gamma. Images can become noticably darker near light-dark transitions, including any areas with high noise. Thin features like antennas need special treatment. Paint over them with a broad brush, using what you imagine to be the oringinal color. (the original color is almost entirely lost to JPEG compression) The original image can sometimes be used as the alpha channel; use of the curves tool on a selection will be required to get the right contrast. For thin features that are nearly horizontal or vertical, complete replacement is required to avoid aliasing. (It's best to locate vertical antennas at locations p*n+x where p is a power of two, n is a per-antenna value, and x is a value shared by all antennas. This ensures that the antennas are all equally blurry or sharp when the image is scaled to common sizes.) _______________________________________________ Tuxpaint-dev mailing list [EMAIL PROTECTED] http://tux4kids.net/mailman/listinfo/tuxpaint-dev
