[mpeg2] Re: colour offsets

[Warren Young <warren@etr-usa.com>]

Frank Rosengart wrote:
> 
> JVC-DV500 camera, put it into EBU-bars mode and wired the Y/C output of 
[snip]
> white           244-247-244
> yellow  185-190-0 

Hmmmm...looks like something in your video chain is stretching the color 
gamut to 0-255.  Video signals are standardized so that there are signal 
ranges understood to be "brighter than white" and "darker than black". 
  You should only be seeing a range of about 16-235 when you map 
calibrated video to RGB.

I would guess that Premiere is doing the gamut stretch so that the video 
looks nice and saturated on your monitor.  Try DVD2AVI instead.  It's an 
MPEG decoder which won't fiddle with the video -- it just decodes it 
literally into an AVI.  This program is somewhat buggy when it comes to 
saving an AVI directly.  If it crashes when you try to save an AVI, the 
workaround is to tell it to save a D2V project instead of an AVI.  Then, 
you need to convert that D2V project to an AVI with a program called 
VFAPI Reader.  Try to open that in Premiere.  If it fails to read the 
virtual AVI correctly, run it through VirtualDub to turn that into a 
real AVI, which Premiere _will_ be able to read.

If, after following this procedure, you still see that 0-247 range, your 
Kfir board is definitely miscalibrated.

You can get DVD2AVI, VFAPI Reader, and VirtualDub at http://doom9.org/ 
in the Downloads section.

I found a calibrated EBU bars image here:

http://www.digivideo.org/kuva/EBU%20Bars%20720x576%20601.jpg

In that file, the values are:

white:   235, 235, 235
yellow:  179, 180, 16
cyan:    16, 180, 181
green:   15, 180, 16
magenta: 181, 16, 180
red:     180, 16, 15
blue:    17, 16, 180
black:   16, 16, 16

As you can see, there are 3 main values with a little bit of variation: 
16, 180, 235.

I then took my _Video Essentials_ DVD, ripped the SMPTE color bars 
pattern off of the disc, and found:

white:   235, 235, 235
yellow:  179, 181, 12
cyan:    13, 181, 181
green:   12, 182, 13
magenta: 182, 15, 181
red:     181, 16, 14
blue:    14, 15, 181
black:   16, 16, 16

The values are very similar.

Since both of these patterns stick to the standard 16-235 range 
(roughly, anyway), they are probably both reasonably close to the proper 
values.  I would suggest that once you can get your video chain to give 
you values similar to these, it will be as close to "correct" as makes 
no difference.
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