LV brightness and contrast with RAW recording - external

[stevefal]

I'd like to record RAW with an external monitor that has it's own waveform, histogram, zebras etc. But I don't understand the relationship between pixel values send via HDMI and the values recorded. I'm under the impression that normally, what I get via HDMI throws 1 bit off the top and the remainder off the bottom. If this is correct, my external monitor would show clipping 1 bit before it's actually happening. Can you correct me on this?

Finally, ML has LV brightness, contrast and saturation settings for the internal monitor, but they do not apply to the external output. Is that a camera limitation, or is it possible to send via HDMI, say the RAW 8 MSBs for highlight preservation, or even a low-contrast version?

[a1ex]

The LiveView image (including HDMI) is the one rendered by Canon - it has white balance and some other curves applied. Canon does not do any highlight recovery (this is the fastest way), and white balance usually multiplies red and blue by around 2 - so around 1 stop from these two channels is clipped in the preview. But the green channel should be more or less OK.

A common workaround for this is to use UniWB - that one will render the RGB clipping points closer to their values in RAW.

You can also adjust the digital ISO component, e.g. 160/200/250 - it will only affect the preview, but not the recorded data (in movie mode RAW, you can only record full-stop ISOs). Picture style settings will also affect the YUV histogram and zebras.

You can send your own image via HDMI, but... good look rendering it in real-time on the ARM processor, or understanding how to use Canon's image processing modules.

Contrast and saturation were found by trial and error - poking DIGIC (ENGIO) registers - http://magiclantern.wikia.com/wiki/Register_Map/Brute_Force - and most of them happened to work only on the built-in LCD (since they are parameters of the LCD controller). And most of these things are broken in 5D3 1.2.3 and require the same trial and error to be re-done from scratch (a lot of display registers changed).

Short answer: for raw-recording, only the raw-based exposure feedback is accurate. But in many cases, YUV-based feedback can be a good approximation.

[stevefal]

Taking your cue from the digital ISO comment, I see that "ML Digital ISO" lets me drop up to -2EV. Is this also not affecting the recorded data? If so it seems I could use it to calibrate HDMI highlight clipping to somewhat match RAW clipping?

[a1ex]

Correct, that's why you don't see any change in the bottom bar.

Turn off RAW recording and you'll see ML digital ISO affecting the overall ISO.

[stevefal]

Works! With about -1EV of ML digital ISO, the RAW zebras almost match the false color highlight pattern on my external monitor. So in the RAW case, ML digital ISO is like HDMI gain to me.

The negative ML digital ISO steps are -0.1, -0.2, ... -0.7, -1.0, -1.5, .2.0.  Are those camera dependent, or is it possible that granularity could be made 0.1 throughout the range?