[Search for users] [Overall Top Noters] [List of all Conferences] [Download this site]

Conference bulova::decw_jan-89_to_nov-90

Title:	DECWINDOWS 26-JAN-89 to 29-NOV-90
Notice:	See 1639.0 for VMS V5.3 kit; 2043.0 for 5.4 IFT kit
Moderator:	STAR::VATNE

Created:	Mon Oct 30 1989
Last Modified:	Mon Dec 31 1990
Last Successful Update:	Fri Jun 06 1997
Number of topics:	3726
Total number of notes:	19516

3198.0. "difference between DEPTH and BITS_PER_PIXEL?" by TPOVC::JOHNNYHO () Mon Aug 13 1990 06:56

    
    There are two fields in XImage structure, depth and bits_per_pixel.
    What's the difference between them? I'm using VAXstation 3520 with 24
    planes. I found out that depth is 24 while bits_per_pixel is 32.
    What's the purpose for the extra 8 bits?
    
    Thanks in advanced!
    
    Johnny

T.R Title User Personal
Name Date Lines

3198.1 DECWIN::FISHER Locutus: Fact or Fraud? Mon Aug 13 1990 11:06 8

T.R	Title	User	Personal Name	Date	Lines
3198.1		DECWIN::FISHER	Locutus: Fact or Fraud?	`Mon Aug 13 1990 11:06`	8
	Depth is the actual number of bits in a pixel that are used. Bits per pixel are the number of bits you have to send including padding. In a FF, and others, it is faster to send pixels 32 bits at a time and just ignore the most significant 8 bits than it is to try to extract 24 bits out of 4 different positions in a longword. It may well be the same with a 4-plane gpx (i.e. depth is 4, but bpp may be 8; I don't rememeber for sure). Burns

Depth is the actual number of bits in a pixel that are used.  Bits per pixel are
the number of bits you have to send including padding.  In a FF, and others, it
is faster to send pixels 32 bits at a time and just ignore the most significant
8 bits than it is to try to extract 24 bits out of 4 different positions in a
longword.  It may well be the same with a 4-plane gpx (i.e. depth is 4, but
bpp may be 8; I don't rememeber for sure).

Burns