improve the contrast of the picture. The "histogram 
equalization" method is commonly used for this purpose. This 
transformation works with separate color components. Having a 
normalized histogram h(x), such that 
f 
>*4 
h(x) = 1 
for one of the components, the transformed level H(x) for 
primary level x will be given by the expression 
x 
H(x) = X. h(i).255 
1*4 
This transformation gives excellent results and can be 
realized on the computer without problems. 
Refining of the pixel size 
The pixel size of TM data (30 x 30 m on the ground) is too 
rough for 1 : 50 000) photomaps (1 pixel 0.6 mm). A lot of 
different methods exists for refining of the pixel size. The 
best results were obtained with our method based on the 
Taylor's development. 
Digital image may be understood as a function f(x,y) of 
coordinates x,y. This function can be approximated with a new 
function f*(x,y) using the grey levels of neighbouring pixels. 
In case of using the Taylor's development, the expression for 
the functiom f*(x+h1,y+h 2 ) will be 
f *(x+hï ,y+h 2 ) = f(x,y) + —-( hijr- + h 2~fç) * f (x, y) + 
+ T! (hl £ + *2fyz.f(x.y) 4- £(hl£ + h 2 ^)3.f(x,y) 
.+ ... + + h 2 ) n * f ( x, y ) 
+ 
The partial derivatives are calculated as 
J^f(x,y) = f(x+1,y) - f(x-1,y) 
^f(x,y) = f(x,y+1) - f(x,y-1) 
One pixel from the original data set will be substituted by 
sexteen new ones with coordinates illustrated in the 
following scheme 
x, y are coordinates of the original pixel. 
Color composite and its superimposition into the map 
Before digital processing of TM data (according to the 
226