IS_GRAY_CMAP Function (PV-WAVE Extreme Advantage)

Image Processing Toolkit User Guide > Reference A–I > IS_GRAY_CMAP Function (PV-WAVE Extreme Advantage)

Determines if a colormap is grayscale.

Usage

result = IS_GRAY_CMAP(colormap)

Input Parameters

colormap—A 3-by-n_colors array containing the colormap, where n_colors is the number of colors in the colormap.

Returned Value

result—A value indicating if the colormap is grayscale as follows:

1—Grayscale colormap

0—Colormap not grayscale

Keywords

Linear—If set, determines if the colormap is monotonically increasing.

Discussion

In a grayscale colormap, the red, green, and blue components are equal to each other for each element in the colormap. Therefore, to test for a grayscale colormap, the following equation is true:

red(i) EQ blue(i) EQ green(i), for 0 ≤ i < n_colors

where n_colors is the number of colors in the colormap.

A grayscale colormap is said to be linear if the grayscale value is monotonically increasing. To determine linearity for a grayscale colormap, it is sufficient to test only the red component as follows:

red(i – 1) < red(i), for 1 ≤ i < n_colors

where n_colors is the number of colors in the colormap.

Example

; Get the current colormap.

TVLCT, r, g, b, /Get

; Put it into a colormap array.

cmap = BYTARR(3, N_ELEMENTS(r))

cmap(0, *) = r

cmap(1, *) = g

cmap(2, *) = b

result = IS_GRAY_CMAP(cmap, /Linear)

; Check to see if it is linear grayscale.

IF result EQ 1 THEN PRINT, 'Colormap is ' + $
'linear grayscale.' $ &

ELSE PRINT, 'Colormap is not linear grayscale.'