On Mon, 2009-11-23 at 12:59 -0700, Michal Jaegermann wrote:
If we are already there then maybe you can explain? :-)
'man -k mode | grep VESA' prints
cvt [] (1) - calculate VESA CVT mode lines
gtf [] (1) - calculate VESA GTF mode lines
but what is a difference? 'man cvt' at least says "VESA Coordinated
Video Timing". V.E.R.A. for a change brings "Generalized Timing
Format (VESA)" when asked for "gtf". I am afraid that this still
does not tell me very much. Results with the same paramaters are
slightly different. 'xvidtune' allows to "tune" an image to your
monitor before you will hit "Show".
They're both timing generation formulas. GTF is older, a bit more
complex, and generally matches the physical requirements of CRTs. CVT
is newer, simpler, and has a cheat code for reduced bandwidth
consumption on LCDs. This is important, among other reasons, because
the DVI link speed is 165MHz:
atropine:~% cvt 1920 1200 60
# 1920x1200 59.88 Hz (CVT 2.30MA) hsync: 74.56 kHz; pclk: 193.25 MHz
Modeline "1920x1200_60.00" 193.25 1920 2056 2256 2592 1200 1203 1209 1245
-hsync +vsync
atropine:~% cvt -r 1920 1200 60
# 1920x1200 59.95 Hz (CVT 2.30MA-R) hsync: 74.04 kHz; pclk: 154.00 MHz
Modeline "1920x1200R" 154.00 1920 1968 2000 2080 1200 1203 1209 1235 +hsync
-vsync
and so a non-reduced-blanking timing for 1920x1200 won't fit on a single
DVI link.
tl;dr version: GTF for CRTs, CVT for LCDs.
- ajax