Can be avoided for the vast majority of a large image. 
Transformations to alternate color coordinate systems provide another 
vehicle for color enhancement for display. A wide variety of color coordinate 
systems beyond the normal tristimulus system (blue, green, red) have been 
devised and used (Wysecki and Stiles, 1967; Pratt, 1978). Chromaticity coor- 
dinates form one convenient system (B-blue, G-green, R-red): 
I=B+G+R 
b = B/I 
g = G/I 
r = R/I 
where intensity I, together with g and r, form the usual independent set 
(B, G, R are the tristimulus values). Chromaticity diagrams (a plot of g 
versus r) provide a useful color analog to single image histograms. Popu- 
lation of a given color (g,r combination) in the image can be plotted as a 
brigthness value at the corresponding point of the chromaticity diagram. 
The distribution of intensity values, not addressed by a chromaticity dia- 
gram, can be plotted as a standard histogram. 
Another system which has proven useful at JPL is a form of hue, satura- 
tion, intensity system (Gillespie in Goetz et al., 1975). Hue and satura- 
tion are perceptually significant quantities and hence can be helpful in 
controlling the display of color. Controlled stretching of hue and satura- 
tion have been used to produce exaggerated color versions of Viking orbiter 
color scenes (Ruiz et al., 1977). Transformations can also be used to norma- 
lize color output from different display device resulting from the use of 
different display primaries. 
Color coordinate transformations also offer certain processing possibi- 
lities. Many of these procedures are based on the separation of color and 
intensity information offered by various of these coordinate systems. Cer- 
tain filtering operations, particularly low frequency notch filtering, are 
best performed on the intensity component only (Soha et al., 1976). A high 
resolution monochromatic image can be substituted as the intensity component 
to modulate the color of & lower resolution scene. Thus, for example, Land- 
sat-RBV intensity could be superimposed upon Landsat-MSS color.This same capability 
offers another method of combining diverse data types. Stromberg in 
Daily et al.,(1978) nas used this approach to combine radar with Landsat data, 
using radar as intensity. Intensity replacement operations of the type 
described can in fact be accomplished without &ctually performing any coordi- 
nate transformation simply by multiplying each tristimulus component by the 
ratio of the replacement intensity over the old intensity. This approach 
is equivalent to performing the operation in chromaticity coordinates (Soha 
et al., 1976). Actual transformation can be reserved for those cases where 
color modification is also desired. 
2. TECHNOLOGIST-USER INTERFACE 
Digital image processing is & technology that originated entirely in the 
computer research and United States'space environment, somewhat remote from 
the user's world of geo-scientists. Attempts in the USA were made early to 
involve users as partners of the technologists. This was only partly success- 
ful. The situation may appear similar in Europe. NASA has been working on 
the problem. Billingsley (1976) has identified the problem in his attempts 
to bridge the gap of image processing experts and geoscientific users(Fig.9). 
   
   
  
   
    
   
   
  
  
  
  
  
     
   
  
  
  
     
   
  
  
  
  
  
  
  
  
  
  
  
  
  
   
    
   
   
  
  
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