ATI AIW 9600XT can capture illegal values: what does that mean exactly?

[Darryl In Canada]

I understand that when capturing video, one should adjust the pro-amp settings in VirtualDub to brightness within the 16–235 range. And to do this, one turns on the histogram in VirtualDub, plays the scene of video, and adjusts the brightness and contrast until the levels are in the safe blue zone, and not in the unsafe red zones on the right and left.

Question: I have read that the ATI 9600XT can capture illegal values (those in the red zone), but that other devices like the ATi600 cannot. Does the ability to capture illegal values mean that slightly blown out whites and darks can be adjusted in post to restore some of the detail? Or does it mean something else?

[jagabo]

Does the ability to capture illegal values mean that slightly blown out whites and darks can be adjusted in post to restore some of the detail?

Yes.

[Sharc]

Question:Does the ability to capture illegal values mean that slightly blown out whites and darks can be adjusted in post to restore some of the detail? Or does it mean something else?

Basically one can correct and restore the levels in post as long as the signals reside within the 0 .... 255 range (verified by means of the histogram and/or the waveform monitor) and are not clipped. Note that clipping may happen at any stage in the signal flow, so one may actually see clipped signals which are within the stated range. Once a signal is clipped the details are lost and can't be recovered.

[jagabo]

Basically one can correct and restore the levels in post as long as the signals reside within the 0 .... 255 range (verified by means of the histogram and/or the waveform monitor) and are not clipped.

Just for clarity, note that values less than 0 and more than 255 can't be represented in 8 bit caps. Any pixels that would have been outside the 0 to 255 range are crushed to those extremes. For example, a pixel that was supposed to be at -20 will be clipped at 0 instead; a pixel that was supposed to be 275 will be clipped at 255. As Sharc said, you want to avoid hard clipping as that will lose details in the dark and light areas, details that you might otherwise be able to recover.

[Darryl In Canada]

Follow up question. I've noticed that when I use my MiniDV camcorder as the digitization device for Video8 footage, I am able to restore blown out whites in post. Does this suggest that MiniDV as a digitizer has the same illegal value pardoning power as the ATI AIW 9600XT

[jagabo]

Follow up question. I've noticed that when I use my MiniDV camcorder as the digitization device for Video8 footage, I am able to restore blown out whites in post. Does this suggest that MiniDV as a digitizer has the same illegal value pardoning power as the ATI AIW 9600XT

In the sense that some bright parts of the image have details between 235 and 255 that can be restored. But it's also the same that any data over 255 will be clamped to 255. And yes, it's quite common for DV devices to have brights up to 255.

[lollo]

I understand that when capturing video, one should adjust the pro-amp settings in VirtualDub to brightness within the 16–235 range. And to do this, one turns on the histogram in VirtualDub, plays the scene of video, and adjusts the brightness and contrast until the levels are in the safe blue zone, and not in the unsafe red zones on the right and left.

Not really. You should adjust the input range in order to be captured by your card. Generally something like 16-252/254. You can see an overview of the most common capture range here: https://www.digitalfaq.com/forum/video-capture/9865-canopus-advc-110-a.html#post62640

After, if you need a RGB conversion for processing or display, you reduce the levels to 16-235 in software, which is more accurate than with the procamp of the cards.

[Sharc]

Not really. You should adjust the input range in order to be captured by your card. Generally something like 16-252/254.
After, if you need a RGB conversion for processing or display, you reduce the levels to 16-235 in software, which is more accurate than with the procamp of the cards.

Take note though that such YUV->RGB (and subsequent RGB->YUV) conversion may - depending on the tool - take place "silently" without one being aware of. Then the damage is there.
Capturing deliberately into the "red" luma zone with useful picture content (means other than halos and noise) is prone to causing trouble IMO, unless one knows exactly what one is doing.

Capturing too cautious on the other hand reduces SNR and may tend towards banding, but we are still talking (S-)VHS quality.....

[lollo]

Take note though that such YUV->RGB (and subsequent RGB->YUV) conversion may - depending on the tool - take place "silently" without one being aware of. Then the damage is there.

Absolutely correct. But somebody going into restoration, should learn, understand and manage those aspects

unless one knows exactly what one is doing

Yes

Capturing too cautious on the other hand reduces SNR and may tend towards banding, but we are still talking (S-)VHS quality

Still noticeable