cquant

    ($out, $lut) = cquant($image [,$ncols]);

This function does color reduction for <=8bit displays and accepts 8bit RGB and 8bit palette images. It does this through an interface to the ppm_quant routine from the pbmplus package that implements the median cut routine which intellegently selects the 'best' colors to represent your image on a <= 8bit display (based on the median cut algorithm). Optional args: $ncols sets the maximum nunmber of colours used for the output image (defaults to 256). There are images where a different color reduction scheme gives better results (it seems this is true for images containing large areas with very smoothly changing colours).

Returns a list containing the new palette image (type PDL_Byte) and the RGB colormap.

interlrgb

    $rgb = $palette_im->interlrgb($lut)

Input should be of an integer type and the lookup table (3,x,...). Will perform the lookup for any N-dimensional input pdl (i.e. 0D, 1D, 2D, ...). Uses the index command but will not dataflow by default. If you want it to dataflow the dataflow_forward flag must be set in the $lut piddle (you can do that by saying $lut->set_dataflow_f(1)).

rgbtogr

   $gr = $rgb->rgbtogr

Performs a conversion of an RGB input image (3,x,....) to a greyscale image (x,.....) using standard formula:

   Grey = 0.301 R + 0.586 G + 0.113 B

bytescl

        $scale = $im->bytescl([$top])

By default $top=255, otherwise you have to give the desired top value as an argument to "bytescl". Normally "bytescl" doesn't rescale data that fits already in the bounds 0..$top (it only does the type conversion if required). If you want to force it to rescale so that the max of the output is at $top and the min at 0 you give a negative $top value to indicate this.