docs(readme): rearrange and edit opening; add alts

README.md

@@ -5,19 +5,26 @@ A jet airplane is taking off in the sky.](bordeaux-15bit.png)
 
 *(The image above has 15-bit color.)*
 
-HiColor is a program for converting images to 15- and 16-bit RGB color, the color depth of old display modes known as [“high color”](https://en.wikipedia.org/wiki/High_color).
+HiColor is a program for converting images to 15- and 16-bit RGB color,
+the color depth of old display modes known as [“high color”](https://en.wikipedia.org/wiki/High_color).
+I wrote because I wanted to create images with the characteristic high-color look.
+
+## Description
+
+HiColor reduces image to 15- or 16-bit color.
 In 15-bit mode images have 5 bits for each of red, green, and blue, and the last bit is reserved.
 In 16-bit mode green, the color the human eye is generally most sensitive to, gets 6 bits.
 
-I wrote this program because I wanted to create images with the characteristic high-color look, and nothing seemed to support high color.
-It implements its own simple [file format](format.md) and converts between this format and PNG.
-It can also convert normal PNG to normal 32-bit PNG with only high-color color values.
+HiColor implements its own simple [file format](format.md) and converts between this format and PNG.
+It can also convert PNG to normal 32-bit PNG with only high-color color values.
 (This simulates a roundtrip through HiColor without creating a temporary file.)
+
 To reduce the quantization error (the difference between the original and the high-color pixel),
 HiColor defaults to the [Bayer ordered dithering](https://bisqwit.iki.fi/story/howto/dither/jy/#StandardOrderedDitheringAlgorithm) algorithm,
 which historical software and hardware used for dithering in high-color mode.
 It can use [“a dither”](https://pippin.gimp.org/a_dither/) instead.
 Dithering can be selected or disabled with command-line flags.
+
 HiColor files have either the extension `.hic` or `.hi5` for 15-bit and `.hi6` for 16-bit respectively.
 
 Quantized images compress better when their originals, so HiColor may serve as a less-lossy alternative to the 256-color [pngquant](https://pngquant.org/).
@@ -100,6 +107,19 @@ sudo apt install -y graphicsmagick tclsh wine
 gmake test-wine
 ```
 
+## Alternatives
+
+I wrote HiColor because nothing seemed to support high color.
+I was wrong about that.
+Actually,
+[FFmpeg](https://www.madox.net/blog/2011/06/06/converting-tofrom-rgb565-in-ubuntu-using-ffmpeg/),
+[GIMP](https://docs.gimp.org/2.10/en/gimp-filter-dither.html),
+and
+[ImageMagick](https://www.imagemagick.org/Usage/quantize/#16bit_colormap)
+can convert images to 15- and 16-bit color.
+Search for "RGB555" and "RGB565" to find such conversions.
+The thing that differentiates HiColor is being a small dedicated tool and an embeddable library.
+
 ## License
 
 MIT.