[net.vvs] VVS image format

lauren (01/26/83)

Greetings.  Welcome to the VVS newsgroup.  Actual images will be made
available shortly.  For now, I thought I'd distribute the image format
documentation, so that image conversion programs can be ready when
the actual pix become available for UUCP access.

Please note that the "vortex!/pix" directory mentioned below is *not*
yet available via UUCP, so don't try access it yet!  Also, please remember
that you must currently have a direct UUCP path to vortex in order to
transfer the image files.

If you have any questions or comments, please let me know.

{ucbvax!lbl-csam, harpo, decvax, randvax, ...}!vortex!lauren


			   Image Format

		      Last updated:  1/24/83

This file is: "vortex!/pix/format".

Currently, all images are stored in a straightforward, non-compressed
format.  Images are digitized as 256 by 256 pixels.  Pixels are
4 bits wide and represent a grayscale value ranging from 0 to F (hex).
For each pixel, 0 represents darkest BLACK, and F represents brightest
WHITE.  The individual bits are weighted in the image for a standard
grayscale: the relative weights are 1 for the most significant bit,
1/2 for the next bit, 1/4 for the next, and 1/8 for the least
significant bit in the pixel.  

Each VVS image file is 32768 bytes long.  The byte stream represents
the scanned video image starting at the upper-lefthand corner of the
image, progressing to the right to the end of the first scan line, then
continuing at the lefthand edge of the second scan line, and so on.

Image layout (bytes):

line 1	      0       1       2       ...      128
line 2	     129     130     131      ...      256
line 256    16256   16257   16258     ...     16384

Each byte contains 2 pixels, with the "first" pixel in the high order
nibble of each byte:

	7 6 5 4     3 2 1 0     7 6 5 4     3 2 1 0
     |	pixel 1	 |  pixel 2  |  pixel 3  |  pixel 4  | ...
	       byte 1	     |	       byte 2

Unless otherwise noted, all current VVS images are digitized to broadcast
video standards: 4:3 aspect ratio with 240 active display lines.  The last
2048 bytes of each image (lines 241 through 256) are set to 0 to provide
full image blanking on standard 256 X 256 graphics displays.  Most current
VVS images have a typical actual pixel value range of 0 through A or B (hex).