This program is part of Netpbm.
ppmwheel produces a PPM image of a color wheel of the specified diameter inside a white square just large enough to hold it.
The color wheel is based on the HSV color model. Hues are distributed angularly around the circle and the values and saturations are distributed radially.
You can generate three kinds of color wheel:
The saturation is 100% everywhere. The value goes from zero to 100% linearly, from the center of the wheel to the edge. So the center is black.
Hence, the image consists of all of the secondary colors based on the red, green, and blue primary colors. A secondary color is one that is composed of light of at most two of the three primary colors.
The value is 100% everywhere. The saturation goes from zero to 100% linearly, from the center of the wheel to the edge. So the center is white.
The saturation is 100% everywhere. The value is a strange function of the distance from the center, increasing as the square root of the distance until halfway out, then decreasing as the 8th root of the distance the rest of the way. We don't know what the point of this is, but it is what the program Ppmcirc by Peter Kirchgessner in 1995 does, and was the only option in ppmwheel from its inception in 2003 to 2019.
You must specify one non-option argument: the radius of the color wheel in pixels.
This is also the height and width of the output image.
In addition to the options common to all programs based on libnetpbm (most notably -quiet, see Common Options), ppmwheel recognizes the following command line options:
This option was new in Netpbm 10.86 (March 2019).
This option was new in Netpbm 10.86 (March 2019).
This option was new in Netpbm 10.86 (March 2019).
ppmwheel was added to Netpbm in Release 10.14 (March 2003).