-nvironment variables:
-
-Color distance function: S2TC_COLORDIST_MODE (default: WAVG)
-RGB: weighted YCbCr difference assuming linear input
-YUV: weighted Y'Cb'Cr' difference assuming sRGB input
-SRGB: weighted YCbCr difference assuming sRGB input
-SRGB_MIXED: weighted "Y'(Y)Cb'Cr'" difference assuming sRGB input
-LAB: L*a*b* difference
-AVG: standard average of component difference (generic)
-WAVG: weighted RGB average of component difference
-NORMALMAP: vector distance after normalization
-
-Color selection: S2TC_RANDOM_COLORS (default: -1)
--1: quick selection (just darkest and brightest color of each block)
-0: normal selection (all 16 colors of each block are candidates)
->0: randomized selection (S2TC_RANDOM_COLORS random colors are added to the
- >candidates for each block)
-
-Color refinement: S2TC_REFINE_COLORS (default: ALWAYS)
-NEVER: never run color refinement
-ALWAYS: always run color refinement (i.e. replace the colors by possibly better
- colors by averaging the original colors for the encoded pixels)
-CHECK: always run color refinement, but only use its result if it is actually
- a closer match for the block
-LOOP: always run color refinement, but only use its result if it is actually
- a closer match for the block; after refining, reassign colors and refine
- till no change for the better happened
+S2TC Environment Variables
+==========================
+
+Color Distance Function
+-----------------------
+The following color distance functions can be selected by setting the
+environment variable `S2TC_COLORDIST_MODE`:
+
+* `RGB`: weighted YCbCr difference assuming linear input
+* `YUV`: weighted Y'Cb'Cr' difference assuming sRGB input
+* `SRGB`: weighted YCbCr difference assuming sRGB input
+* `SRGB_MIXED`: weighted "Y'(Y)Cb'Cr'" difference assuming sRGB input
+* `AVG`: standard average of component difference (generic)
+* `WAVG`: weighted RGB average of component difference
+* `W0AVG`: superfast weighted RGB average of component difference
+* `NORMALMAP`: vector distance after normalization
+
+The default is `WAVG`, which is a good compromise between speed and quality for
+RGB and sRGB data. For optimum quality on sRGB input, try `SRGB_MIXED`.
+
+The color distance function defines how "closeness" of pixel values is judged
+when the pixel color values are evaluated, colors are selected, or during
+refinement.
+
+Color Selection
+---------------
+The environment variable `S2TC_RANDOM_COLORS` can be set the following way:
+
+* `-1`: quick selection (darkest and brightest color are chosen, which is
+ similar to the method in the Color Cell Compression paper)
+* `0`: all 16 input colors of a block are considered
+* greater than `0`: additionally, that many random color values in the range
+ of the input color values are considered
+
+The default is `-1`, which is fast but poor quality, however ideally suited for
+online compression. For optimum quality, try `64`.
+
+A bad color selection can later be compensated for by color refinement.
+
+Color Refinement
+----------------
+The environment variable `S2TC_REFINE_COLORS` can be set to the following values:
+
+* `NEVER`: never run color refinement
+* `ALWAYS`: unconditionally perform color refinement
+* `LOOP`: perform color refinement, evaluate its output and discard it if it
+ didn't improve quality, re-evaluate the pixel color values, and repeat
+ until no improvement could be made
+
+The default is `ALWAYS`, which is fast and decent quality, and usually doesn't
+make things worse. For optimum quality, try `LOOP`.
+
+Color refinement recalculates the color palette of a block after the pixel
+value decision by averaging the color values of those encoded as c0 or c1, and
+is a technique that helps a lot of the initial color selection was poor (e.g.
+if `S2TC_RANDOM_COLORS` was not set, or set to `-1`).
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