Dissolve vs. Crossfade differences

jasman wrote on 8/7/2005, 4:59 PM
I was having problems with unwanted black and white level shifts during dissolves and crossfades. I did some controlled experiments with pure black and white images using 0 IRE = 16,16,16, 100 IRE = 235,235,235 samples, contrasting this with samples where blk =0,0,0 and white =255,255,255.

Results:
1. Standard crossfades are setup for video black = 0 IRE and white = 100 IRE. You can use them with digital 0,255 signals but the results will be skewed, depending on content.

2. The Sony dissolve transition is set up for digital levels 0 blk and 255 wht. It will bloom with IRE 0 and 100 signals. By bloom I mean black level comes up and white level goes down.

I don't believe I'm hallucinating, and I do believe this is pretty important to know. Anyone else see this? Is this common knowledge?

Comments

GlennChan wrote on 8/7/2005, 7:29 PM
I do notice that fades to black go to 0 0 0 black (in Vegas RGB units), which would be lower than where blacks are supposed to be for a digital format (black should have a luma value of 16 if you're working with DV).
By fade to black, I mean the following:
Throw a clip onto the timeline.
Click on the upper right corner of that clip, and drag left.


2- I'm not seeing the same results as you.

With the standard fades (where you click-drag the upper corners of a clip), the levels work like they're supposed to whether you're working with 0-255 (computer) or 16-235 (DV) material.

Maybe your setup is accidentally using the Microsoft DV codec?

Vegas should be set to:
Ignore third party DV codecs
Uncheck "Use Microsoft DV codec"


I find that a lot of things in Vegas assume 0-255. If you want a fade to black to have proper levels, then add a 16 16 16 black solid color underneath. Use parent/child relationships if you are using compositing modes.

3- Which dissolve type are you using with the "Sony Dissolve" transition?
Coursedesign wrote on 8/7/2005, 8:18 PM
black should have a luma value of 16 if you're working with DV

The 16-235 crippling of the video signal is only for U.S. NTSC broadcast.

This seriously degrades the picture, but of course most people don't notice it unless they are able to access broadcast stations that don't use this ugly historical feature (there are several in Los Angeles for example).

It was created to help the cheapest possible tube TVs of the era deliver a useable picture even when their internal oversimplified circuitry couldn't handle normal signals properly. Compare this with how the NTSC 1953 color system actually specified a significantly larger color space back then than either the Rec. 601 of today's standard definition TV or the Rec. 709 used for HDTV....

When you output to digital formats (such as DVD and others), the range should normally be 0-255. If there is an anal-og TV involved, it will usually need to have at least the 7.5 IRE setup added (that's 16 in digital), otherwise the picture will be too dark.

Note that many DVD players nowadays can be set to output an analog signal with or without setup.

Edit added:
Some DV cameras have a video setup option, usually hidden in a submenu somewhere. This option is only for the analog video output on the camera, for use when hooking it up to an American NTSC TV (needs setup) or a Japanese TV (no setup). It does not affect what's recorded on the DV tape.

PAL never used setup.
johnmeyer wrote on 8/7/2005, 8:54 PM
There is a plugin for doing "film style optical transitions." It was referenced in this thread:

Film Style Optical Transition Plugin
Coursedesign wrote on 8/7/2005, 9:12 PM
Yes, the free SMLuminance optical dissolve plugin works great in Vegas.

It looks VASTLY better than a regular digital dissolve IMHO.
jasman wrote on 8/7/2005, 9:34 PM
Okay, I was hallucinating. I was using the sony additive dissolve and it does what it says, not what I expected. Intentional blooming is what I'd call it.

I did discover a bug in the standard set of crossfades. You can try it yourself. Crossfade two solid events of the same color with digital values r,g,b from 1 - 255. You should get the same color and values r,g,b during the crossfade, but you'll see that you get r-1, g-1, b-1. For 0 values it works because -1 is not allowed. So during the crossfade the image actually gets slightly darker by one digital code. I can most definitely see this!

The film style optical dissolve plug-in works great, it does not have this problem.