Why are Preview Window (levels) Incorrect?

Andy_L wrote on 10/3/2009, 9:40 AM
Okay,

I understand the Preview Window displays video in the computer RGB space while the Windows Secondary Display shows video RGB (if you check that option). So, according to the Vegas manual, the Preview Window is "incorrect".

What I don't understand is why this is so. How is this desirable behavior from a design point of view? I'm just baffled by this. Under what circumstances do I want my preview window showing an incorrect image?

As far as I can tell, the only way to get the preview window to show video levels is to apply an output levels FX filter converting studio to computer. The obvious pitfall of this approach, however, is that I'll almost certainly forget to remove the FX before rendering video, which will muck up the output file.

Wouldn't it be more appropriate for the Preview Window to match the output of the secondary display options?

Comments

GlennChan wrote on 10/3/2009, 1:08 PM
Wouldn't it be more appropriate for the Preview Window to match the output of the secondary display options?
In my opinion, YES!!!

Seeing the incorrect image is confusing.

The obvious pitfall of this approach, however, is that I'll almost certainly forget to remove the FX before rendering video, which will muck up the output file.
I find the video preview FX dangerous for that reason and generally try to avoid it.


If you are outputting to video, preview over firewire to an external monitor. You want to preview on a video monitor to catch issues like field order, overscan, etc. That's how I deal with it.
Andy_L wrote on 10/3/2009, 4:21 PM
Thanks for your thoughts, Glenn! It would be nice if there were a preview window fx option (which only affected preview), rather than just a master output bus. Or just a checkbox to match displays!
farss wrote on 10/3/2009, 4:47 PM
Totally agree with Glenn except for one thing. The Preview window is really there for judging edits, not color correcting. It makes little sense to sweat too much over how it looks and you're quite likely to adjust the monitor which has the T/L, Preview etc to be easy on your eyes. Also bit of a waste having an expensive video monitor displaying all that other stuff. Makes more sense to have an external monitor that's calibrated and left alone for making critical grading decisions.

Bob.
winrockpost wrote on 10/3/2009, 6:17 PM
" have an external monitor that's calibrated '
yep! totally agree, few however take the time,, and if its not set correctly may as well just use the preview monitor
Laurence wrote on 10/3/2009, 9:08 PM
>If you are outputting to video, preview over firewire to an external monitor. You want to preview on a video monitor to catch issues like field order, overscan, etc. That's how I deal with it.

Great advice for SD and the way I always did it. Since going HD I've been back on the Vegas monitor preview window though.
Laurence wrote on 10/3/2009, 9:09 PM
One problem with putting temporary color correction on the preview window is that it over corrects generated media like titles and animated photos which are already at cRGB levels.

Another issue is that many of us want to HD cRGB renders for Vimeo, Youtube or Facebook. For these, the cRGB preview of Vegas is perfect.

These are exactly the issues I've been talking about in http://www.sonycreativesoftware.com/forums/ShowMessage.asp?MessageID=676484&Replies=19this[/link] thread, and why I came up with that particular solution. If anyone has any better ideas, I would love to learn them.
Andy_L wrote on 10/4/2009, 7:28 AM
One problem with putting temporary color correction on the preview window is that it over corrects generated media like titles and animated photos which are already at cRGB levels

This is only so if you are exporting to computer levels, in which case the preview window would already be showing the correct colors/density for output...except that, as far as I can tell, the workspace including the preview window is not color-managed, so you will still see small but noticeable differences between it and a calibrated secondary display. :(

One other thing: for the FX on the output bus approach (to show video levels on the preview window), the smarter plugin is probably Broadcast Colors. This won't mess up the secondary display when the s.d. is set to show studio RGB.

(I think)
Laurence wrote on 10/5/2009, 8:44 AM

One problem with putting temporary color correction on the preview window is that it over corrects generated media like titles and animated photos which are already at cRGB levels

No, when I preview titles and animated photos with the sRGB to cRGB correction in place, they are oversaturated because cRGB is run through an unnecessary redundant conversion. You can get around this by changing the default blacks and whites on the text media generator 16,16,16 for the blacks (instead of the default 0,0,0) and 235,235,235 for the whites (instead of the the default 255,255,255). You also need to run any photos through a cRGB to sRGB color corrector on either the track or the event. This cancels out when viewed through the preview color correction.

One other thing: for the FX on the output bus approach (to show video levels on the preview window), the smarter plugin is probably Broadcast Colors. This won't mess up the secondary display when the s.d. is set to show studio RGB.

There are two problems with this. First, the Broadcast Colors filter just limits the top and bottom colors rather than shrinking the range evenly. Second, adding this filter will keep the video from smart-rendering when you do an HDV mpeg2 render. That is also why I think that adding the extra track at the bottom of 16,16,16 black is a better way than trying to limit the blacks with a filter.
Andy_L wrote on 10/5/2009, 9:36 AM
There are two problems with this. First, the Broadcast Colors filter just limits the top and bottom colors rather than shrinking the range evenly

This is actually the preferred behavior. Remember, we're only interested in a specific issue here: making the workspace video preview *look* like the secondary display preview (when set to studio RGB). We're not trying to correct video at this point -- just get the displays to match. Ideally, Vegas would allow us to apply fx to the preview only, with no effect on the actual video bus output, but it doesn't. The Broadcast colors suggestion is therefore just an imperfect solution to a problem that shouldn't exist in the first place.

Your comment that adding the filter forces a recompress on render is well taken, though in practice none of my workflows benefit from smart rendering.