Scopes settings?

DataMeister wrote on 6/19/2004, 9:07 AM
Ok. So what exactly do the setting in the scopes accomplish? From what the manual says, I gathered that the studio RGB check box would (for example) strech or compress the histogram to 16 for pure black and 235 for pure white.

Yet, when I check the box I get nothing visual to verify that anything changes. My histogram stays the same as before.

Secondly, what is IRE Setup? What is being set up in the pro sets like the manual is refering to?

JBJones

Comments

vicmilt wrote on 6/19/2004, 11:17 AM
While I'm sure that someone else will be able to better explain...
(this is just from experience - I'm not an engineer, and this is definitely an engineering issue).
So...
When you create video for broadcast, you MUST conform to having the bottom or "blackest black" at an IRE of 7.5 (thus "professional").

If you send tape with a black lower than 7.5 (called sub-black), it will often be returned as unacceptable.

In the bad old days, before non-linear computer generated effects, etc, we used this portion of sub-black as a keying or alpha layer for titles. But once the titles were implemented, we would layback the videotape at an IRE of 7.5 for release.

If you are only producing for DVD, VHS or home delivery of any kind, an IRE of zero is not only acceptable, but acually gives you an extended range of luminance (although I doubt you will actually SEE a difference on your TV screen).
BillyBoy wrote on 6/19/2004, 1:26 PM
Just to clear up what the scopes do...

They're reactive in that they respond in real time if you set them to show how certain filters effect your video. In other words there's no knobs on the scopes that effect your video, the changes you make to the video effect the readouts on the scopes

The vectorscope markings match the markings on the color wheels on the color corrector filter and the color corrector secondary. If you drop the included color bar test pattern on the timeline and look at it in the vectorscope you should see a dot dead center plus one tiny dot dead center in the middle of each major color range.

Where the pattern falls for real world videos depends on the makeup of the video. A image that has lots of blue will be shifted in that direction, one with lots of reds and yellow will be shifted in that direction. One useful feature of the vectorscope is to see color shading. As you watch the scope and tweak the color wheels you'll get feedback. Not the best way to adjust, but you can see the effect.

The other two scopes, the waveform and histogram both set to show luminance values can tell you at a glance if something is obvously off.

The waveform is a vertical scale calibrated as a percentage to show luminance. Because you can make videos for the web, DVD's, CD's, etc.. with Vegas, you can add more luminance if the medium you're working for will accept it. For projects ending up to be viewed off a TV, especially broadcast should generally stay within the 0-100% boundries.

The histogram can show lumiance as a representation of 255 levels, left most (shadows), rightmost (highlights) so you see at a glance what relationships there are to dark, midtone and bright regions. These can be adjusted with color curves or gamma and gain on color corrector along with tweaked with several other filters as well.
DataMeister wrote on 6/21/2004, 8:58 AM
So. What do those little check boxes do in the scope settings? I can not see a change in the scope read out (which I would expect) or in the video image (I would not expect).

JBJones
BillyBoy wrote on 6/21/2004, 11:43 AM
You mean the 7.5 IRE and Studio choices? I don't see any difference in the scopes either.
smhontz wrote on 6/21/2004, 12:16 PM
The checkboxes are there for you to decide how you want to calibrate your scope.

You can see the effect of the checkboxes by looking at the waveform scope. Drag a solid white color (RGB=255) and a solid black color (RGB = 0) to the timeline and put your cursor in each one in turn while watching the scopes and checking/unchecking the boxes.

If you are producing for broadcast, your RGB values should fall only in the range of 16-235. So, if you set your checkboxes to have "Studio RGB" checked, then a value of 16 (black) corresponds to 0 on the waveform monitor and a value of 235 (white) corresponds to 100. So, you can then check your video and make sure everything falls between 0 and 100. If you have footage that dips below 0 (superblack) or above 100 (superwhite) then you'll have problems.
BillyBoy wrote on 6/21/2004, 12:52 PM
Thanks, I never thought to try a solid white or black and just did a few quick tests and didn't see any noticeable difference with "normal" videos.
farss wrote on 6/21/2004, 1:32 PM
Think this has been covered before but still worth a mention. There's no setup in DV land. Caused a bit of confusion where my mate works, the scopes on the router monitor the SDI feeds yet a lot of other scopes are on analogue feeds so on the same signal there's a difference on the scopes depending on where you look at the signal. Not helped by the fact that they mostly work with PAL so when they have to handle NTSC they are already on uncertain ground.
addavis wrote on 6/21/2004, 1:40 PM
The 7.5 box is useful, in the waveform monitor and if using NTSC, as a visual indicator of the luma values depending on whether the end use will have 7.5 setup added or not..

If you capture NTSC analog or your dv camera adds setup, add this video to VV timeline and open waveform monitor, do not select the "7.5 setup" box and your blacks should indicate around 7.5%. If you are producing for broadcast tape, this is good. However; if producing DVD's and the DVD player will also add setup, you will end up with your blacks at around 15% - not good. So if your end use device adds 7.5 IRE, simply check the "7.5 setup" box in VV scopes to give you an accurate indication of where your blacks will be.