Set the value of a pixel in a run of pixels
int PiSetPixelInData( char *data, int type, unsigned short pixel, unsigned long value );
This function is similar to PiSetPixel(), except that PiSetPixelInData() sets the value of a pixel in a run of pixels pointed to by data, instead of in an image. The type argument indicates the format of the data and must correspond to one of the supported image types, as listed for PhImage_t. The pixel argument is the index of the pixel into the run of data, and value is the new value for the pixel.
PiGetPixel(), PiGetPixelFromData(), PiGetPixelRGB(), PiSetPixel()
“Images” in the Raw Drawing and Animation chapter of the Photon Programmer's Guide