Pro Color_On_Gray, image_1, image_2

   ; Get the data sets if needed.

IF N_Params() EQ 0 THEN BEGIN
   image_1 = Loaddata(7)
   image_2 = Loaddata(5)
ENDIF

   ; Undecomposed color.

IF (!D.Flags AND 256) NE 0 THEN Device, Decomposed=0

   ; Size the second image to fit the first.

s = Size(image_1, /Dimensions)
image_2 = Congrid(image_2, s[0], s[1], /Interp)

   ; Load the color tables. Gray-scale and red-temperature.

ncolors = !D.Table_Size
halfcolors = Byte(ncolors / 2)
LoadCT, 0, NColors=halfcolors
LoadCT, 3, NColors=halfcolors, Bottom=halfcolors

   ; Scale the data. Image_1 data uses gray-scale.

image_1 = Bytscl(image_1, Top=halfcolors-1)
image_2 = Bytscl(image_2, Top=halfcolors-1) + halfcolors

   ; Create a vector for pixelation.

x = Findgen(s[0]/2) * 2

   ; Pixelate the image.

image = BytArr(s[0], s[1])
image[x, *]   = image_1[x, *]
image[x+1, *] = image_2[x+1, *]
image[*, x]   = Shift(image[*, x], 1)

Window, XSize=s[0], YSize=s[1], /Free
TV, image

END