Video Scope Calibration

[brian]

@Austin Thank you so much for this incredibly informative explanation.

If you have the time/interest, it would be incredible to adapt some parts of that write up into the documentation sections:

Video Waveform Scope

Shotcut provides a video waveform scope to aid in setting video levels. [image] See Video Scopes for general information about video scopes. The waveform scope displays graticules for 100 and 0 IRE. These graticules are hard fixed to a Y value of 16 = 0 IRE and a Y value of 235 = 100 IRE. These assignments are not user configurable. While IRE is technically an analog video construct, it is included in this scope as a familiar and useful indicator for video levels.

and

Video Zoom Scope

Shotcut provides a video zoom scope to aid in inspecting images. [image] See Video Scopes for general information about video scopes. The video zoom scope receives YUV 4:2:0 images from the preview player and converts the image to a zoomed in window as RGB. The mouse cursor allows the user to select individual pixels and shows the x,y position, YUV values, and converted RGB values. NOTE: For RGB sources, some chroma bleeding occurs due to the conversion from 4:2:0 to RGB. This can be demons…

@Austin

However, an important distinction is that BT.709 IRE as illustrated so far represents limited-range YCbCr (16-235), whereas sRGB IRE represents full-range RGB (0-255).

This is a critical distinction that applies to Shotcut. When Shotcut operates on YUV, it operates in limited-range. When Shotcut operates on RGB, it operates on full-range. I think this meets most people’s expectations. But it may not meet the expectations of people who come from a deep broadcast TV background.

@Austin

The BT.709 specification describes both full-range and limited-range signals.

Can you elaborate on this specific point? When I look at BT.709, Table 4.6 shows the quantization levels:

It doesn’t seem to leave any provision for full range.

I think it would be more accurate to say that BT.709 describes limited-range signals and sRGB (IEC 61966-2-1:1999) describes full-range signals. Maybe you have a better understanding of where full and limited range values are defined.

Thanks again for your thoughtful response on this topic.