Sims 3 Talk:Creating Custom Clothing Stencils

You might need to add an alternate to the last step of part 3 and all of part 4 for GIMP users. Most the rest is the same, but the way GIMP handles alpha channel is a little different than Photoshop.

In part 3 step 3, if you flatten the image, any transparency of the visible channels is discarded, so all that nice work you did cleaning up the edges of the picture will be lost. Instead, if you just delete the other layers, you end up with an image with one layer which has transparency.

For part 4, in GIMP, if you have transparency you have an alpha channel. So as long as you don't flatten the image, all of part 4 is unnecessary for GIMP users. Tiger 04:37, 24 June 2009 (CDT)

Gimp, Transparency, and DXT1 compression

So, I just cleaned up a lot of the Gimp-centric instructions there, because frankly, they were doing it the hard way. There's one thing I'm going to comment on here, but I'm not going to put anything on that page about yet. Sims3 seems to treat the alpha channel applied to stencils as an all-or-nothing proposition only 1-bit deep, instead of the 8-bits of granularity the image actually contains. Folks may wish to hit up Colors->Components->Decompose to break the image into explicit (and monochromatic) RGBA layers, and then use Colors->Brightness/Contrast on the alpha layer to max out the contrast and eliminate all "partially-there" pixels. Hit Colors->Components->Compose and the RGBA representation "folds up" and back into your "normal" image. I'm still working on whether or not DXT1 or a bug in the plugin is resulting in some other weird artifacting in the alpha channel layer. I don't want to document that hack without being sure when & why someone would need to do it. -- Dagmar d'Surreal 07:05, 27 June 2009 (CDT)

DXT1 by definition has only one bit of alpha - it's either fully visible or fully transparent. So you only get sharp edges. If you want more you can use DXT3 which has 16 levels of transparency, or DXT5 which has a full 8 bits of alpha (But with DXT1 style compression applied separately to the alpha channel.) If you really want to make something smoothly variant in the transparency, your only option is DXT5.
As far as preparing the image for the 1 bit alpha channel, the best way in GIMP is to right click on the image, select "Layer/Transparency/Threshold Alpha", and it gives you a slider to set exactly where the cut off between transparent and not transparent is. Once you hit OK, the alpha channel is given hard edges. Tiger 11:03, 1 July 2009 (CDT)

What's Part Four about anyway

I mean, I totally don't get how one could manage to misalign the alpha layer unless you were for some reason hand-drawing it instead of just carving up a layer with an alpha channel. There's an order in which doing things is easy, and an order in which doing things can be described as "hard headed". Not making sure the image first has an alpha layer so than you can cut pieces away with any of the selection tools and then trying to create an alpha layer to go with it is of the hard-headed and not easy variety. -- Dagmar d'Surreal 06:49, 1 July 2009 (CDT)

...er... that having been said, since Sims likes to muff the edges of some things (which might be the fault of the DXT compression), it's sometimes handy to decompose the image and then tweak the alpha layer with the Brightness & Contrast tool, effectively reducing the bit-depth of the alpha channel to 1. -- Dagmar d'Surreal 06:52, 1 July 2009 (CDT)