perm filename PAGE20[00,BGB] blob
sn#046252 filedate 1973-06-05 generic text, type T, neo UTF8
~F8DATA STRUCTURE: IMAGE ARRAYS.
There are five arrays in CRE: TVBUF, Television Buffer; PAC,
Picture Accumulator; VSEG, vertical segments; HSEG, horizontal
segments; and SKY, background sky blue array. The dimensions are:
FIVE ARRAYS.
1. TVBUF - 216 rows, 288 columns of 6 bit bytes.
2. PAC - 216 rows, 288 columns of 1 bit bytes.
3. VSEG - 216 rows, 289 columns of 1 bit bytes.
4. HSEG - 217 rows, 288 columns of 1 bit bytes.
5. SKY - 216 rows, 289 columns of 18 bit bytes.
Inside CRE, the video image size was fixed at 216 rows of
288 columns of 6 bits per pixel. My original idea was to write a
vision operator that would be applied on a small fixed sized window;
so I have had windows 2 by 2; 2 by 3; 4 by 9; 32 by 36; 72 by 96;
and 216 by 288. That is 216=2*2*2*3*3*3 and 288=2*2*2*2*2*3*3.
Having a fixed window size avoids a morass of word packing, array
allocation and window splicing. Having a window size constructed
out of powers of 2 and 3 simplifies what word packing is required
and allows me to do area and space computations in my head.
The image arrays of CRE are of course two dimensional with
the coordinates in row and columns. Row number increases going down
image, in the negative Y axis direction, which is also called the
direction south. Column numbers increase going right on the image,
in the positive X axis direction, which is also called the direction
east. Video picture elements, or "pixels" are thought of as
expressing the intensity of a square cell; the cells are numbered
from 0 to 215 rows, 0 to 287 columns; the number of a cell is the
grid locus of its upper left (northwest) corner; the center locus of
a cell is at (row+1/5,col+1/2). A pixel cell is surrounded by four
segments; the horizontal segments are numbered 0 to 216 rows, 0 to
287 columns; the number of an HSEG is the grid locus of its left
(west) end point. The vertical segments are numbered 0 to 215 rows,
0 to 288 columns; the number of a VSEG is the grid locus of its
upper (north) end point. These conventions are suggested in the
diagram at the bottom of page 19. ~I1973,800;F8- 20 -