I'd expect more entries about techniques and patterns found both in tools and workflows and in images. Here's a first draft of two important ones:
Pillow ShadingUnrealistic shading of a smoothly curved object by distributing light and dark colors according to the shape of the object's outline instead of imagining and matching the shape of actual isophotes and the location of highlights; this normally results in approximately parallel and constant width color bands from the outline inwards, vastly different from the bunched up, interrupted, expanded and nonconvex shapes of correct shading.
A rectangular pillow is one of the rare cases in which the incorrect but easy procedure sometimes approaches a correct result.
Index PaintingEditing palette indexes instead of pixel colors; it implies caring about palette organization (two palettes with the same colors in a different order are different) and not only about limiting the available colors.
Deliberate attention for building the final image through an explicit indirect mapping mechanism can have a variety of benefits and purposes, mostly related to determining actual colors after editing the image:
- Making images that can be displayed with different but "parallel" palettes (as typical of many videogames with recolored sprites, which can be implemented with a simple palette swap).
- Distinguishing palette indexes in order to treat identical colors as logically different, for example because they are shades in different color ramps.
- Caring about the use of palette entries rather than their actual color (e.g. "I need three entries for flesh, eyes and pupils and I'll reuse hair colors for irises" vs. "I need three entries for rosy pink, blueish white and pure black"); palette structure can be more important and more stable than the contained colors.
- Controlling palette indices exactly (as opposed to letting the paint program manage them automatically) because they also have some conventional meaning: transparency (e.g. index 0 is transparent), metadata about a game sprite such as whether a pixel is a solid part of an object, special display-time palette tricks (e.g. indexes in a certain range are subject to color cycling) and so on.
- Allowing use of tools, like semi-transparent brushes, compositing transparent layers, blurring, etc. that are fundamentally unsuitable for simple palette-based image representations. For example, editing a high bit depth greyscale image and mapping grey ranges to palette colors, as popularized by Dan Fessler (1,2).
1.
http://www.danfessler.com/blog/pixel-purism-process-vs-results2.
http://www.danfessler.com/blog/hd-index-painting-in-photoshop