Screens with a shadow mask behave in a different way. 
With these screens there is no change in the dimensions 
of the electron beam, because the apertures on the 
shadow mask have a fixed interspace, the so-called dot 
pitch. Therefore, regardless of the selected screen 
resolution, the electron beam must travel through all 
apertures of the mask. Individual rows and pixels are 
determined through calculation. The number of rows can 
be determined by dividing the theoretical height of the 
screen with the number of rows in the selected resolution. 
Screens with a tension mask 
15" 
20" 
Resolution 
a (mm) 
b (mm) 
a (mm) 
b (mm) 
640x480 
0,44 
0,60 
800x600 
0,32 
0,44 
1024x768 
0,25 
0,26 
0,30 
0,34 
1152x864 
0,22 
0,26 
1280x1024 
0,20 
0,20 
Table 2: Sizes of screen pixels in screens with a 
tension mask. 
3. ANALYSIS OF RASTER DISPLAYS 
ON THE SCREEN 
For the analysis of a display in raster form, it is important 
to know how pixels are re-calculated, i.e., transformed into 
screen pixels. 
The CRT screens that are currently most frequently 
present on the market are raster oriented. Each screen 
pixel has a more or less great corresponding memory 
area in the frame buffer, which is marked as pixel or scan 
pixel. 
A complete image, formed by means of either raster 
graphics or vector graphics, is composed on the screen 
by means of rasters. Rasters are horizontal scan lines 
consisting of individual scan pixels. Bitmap is the 
expression referring to a raster on monochromatic 
screens, and pixmap is the expression used for the raster 
on color screens. 
3.1 Interdependence of Scan Pixels and Screen Pixels 
The form of scan pixel differs from that of a screen pixel. 
Scan pixels are square in form, whereas the screen pixels 
are either rectangular or triangular, as it has been 
described in chapter 2. 
The way in which scan pixels are translated into screen 
pixels is best explained through the function of zooming, 
i.e., of increasing - “zoom in” or decreasing - “zoom out”, 
which shall in the following text be shown on 15” and 20” 
screens with a tension mask and on a 17” screen with a 
shadow mask. 
The starting point for the research is the 100% translating 
of a raster graphic, where one scan pixel has a mach in 
only one screen pixel. 
Tables 3 and 4 show the measured values on 15” and 20” 
screens with tension masks. The observation during work 
with integer number increases (n x 100% zoom in) and 
regardless of the selected resolution has shown that the 
number of screen rows corresponds with an n-times 
increased number of rows of the increased scan pixel. At 
a double increase (200% zoom in) scan pixel is translated 
into two screen rows; at a sixteenfold increase (1600% 
zoom in) a scan pixel is translated into sixteen screen 
rows. The number of columns is determined in a Way as 
to result in a square transfer of the increased screen pixel. 
This is achieved through multiplication of the number of 
rows by the height of screen pixels; the acquired value is 
then divided by the width of the screen pixel and the result 
expressed with a round number gives the number of 
columns. 
Measured values on a 15" screen with tension mask 
Resolution 
640x480 
1024x768 
1280x1024 
Screen pix 
0,25x0,44 
0,25x0,26 
0,25x0,20 
Increase 
“zoom in” 
n 
s 
n 
s 
n 
s 
mm 
mm 
mm 
mm 
mm 
mm 
1600% 
16 
(7,04) 
25 
(6,25) 
16 
(4,16) 
16-17 
4,0-4,25 
16 
(3,20) 
13 
(3,25) 
1200% 
12 
(5,28) 
18-19 
4,5-4,75 
12 
(3,12) 
12-13. 
3,0-3,25 
12 
(2,40) 
9-10 
2,25-2,5 
800% 
8 
(3,52) 
12-13 
3-3,25 
8 
(2,08) 
8 
(2,00) 
8 
(1,60) 
6-7 
1,5-1,75 
300% 
3 
(1,32) 
4-5 
1-1,25 
3 
(0,78) 
3 
(0,75) 
3 
(0,60) 
2-3 
0,5-0,75 
200% 
2 
(0,88) 
3 
(0,75) 
2 
(0,52) 
2 
(0,50) 
2 
(0,40) 
2 
(0,50) 
100% 
1 
(0,44) 
1 
(0,25) 
1 
(0,26) 
1 
(0,25) 
1 
(0,20) 
1 
(0,25) 
n = number of rows; s = number of columns 
Table 3: Effects of the zoom function on a 15” screen with 
tension mask. 
Measured values on a 20" screen with tension mask 
Resolution 
640x480 
1024x768 
1280x1024 
Screen pix 
0,30x0,60 
0,30x0,34 
0,30x0,20 
Increase 
“zoom in” 
n 
s 
n 
s 
n 
s 
mm 
mm 
mm 
mm 
mm 
mm 
1600% 
16 
(9,60) 
29 
(8,70) 
16 
(5,44) 
18 
(5,40) 
16 
(3,20) 
13 
(3,90) 
1200% 
12 
(7,20) 
22 
(6,60) 
12 
(4,08) 
13-14 
3,9-4,2 
12 
(2,40) 
10 
(3,00) 
800% 
8 
(4,80) 
14 
(4,20) 
8 
(2,72) 
9 
(2,70) 
8 
(1,60) 
6 
(1,80) 
300% 
3 
(1,80) 
5 
(1,50) 
3 
(1,02) 
3 
(0,90) 
3 
(0,60) 
2 
(0,60) 
200% 
2 
(1,20) 
3 
(0,90) 
2 
(0,68) 
2 
(0,60) 
2 
(0,40) 
2 
(0,60) 
100% 
1 
(0,60) 
1 
(0,30) 
1 
(0,34) 
1 
(0,30) 
1 
(0,20) 
1 
(0,30) 
n = number of rows; s = number of columns 
Table 4: Effects of the zoom function on a 20” screen 
with tension mask. 
Table 5 gives an account of the measured values on a 17” 
screen with shadow mask. It is noticeable that for the 
screens with shadow mask it is not possible to determine 
the dependence between the increases on the screen and 
the number of rows and columns without executing a 
mathematical analysis. 
The first step in this analysis is the determination of the 
theoretical size of a screen pixel. Table 6 contains 
theoretical sizes of screen pixels on a 17” screen with 
shadow mask, while details on the procedure in which 
these theoretical sizes are calculated can be found in 
Malic (1998).