Negative ML digital ISO and zebras

[c2s07]

Hello,

First of all, this thread is not about shooting RAW video (so any thoughts related to RAW video shooting may not apply).

When you use negative values for ML digital ISO, the clipped highlights of course get clamped more as you lower the value. I understand that it's how it works, as ML digital ISO doesn't make truly lower analog ISOs, no problem with that.

However, this reduces the effectiviness of the zebras overlay. If you're using 100%/255 for the overexposure limit (for maximum precision), zebras won't display after the effect of negative ML digital ISO is applied. That's because the clipped highlights are now clamped, and since no pixel will ever be able to reach 100% brightness, zebras will not trigger.

I can always lower the zebras overexposure threshold in relation with negative ML ISO; doing this won't make the zebras 100% accurate, but at least you can see them again.

Is there anything else that can be done, or perhaps looked forward to in the future versions?

[RTLdan]

Someone with more technical knowledge will jump in soon here I'm sure...
but I have -0.3 ML Negative Gain + Zebras at 99% and I'm seeing them just fine.

I tried to take a screeshot to prove it, but for some reason the zebra overlay didn't come out of the PPM.

-Daniel

[a1ex]

The exact clipping point depends on picture style settings, so it's hard to tell the best threshold without trial and error.

It might also be camera-specific.

A calibration routine might help (point the camera to something overexposed, and recommend a threshold).

[c2s07]

For finding the threshold, I was thinking of suggesting a new histogram option for showing the brightest level present, but I noticed that the spotmeter set to percent unit seems to work well for that purpose. And it's correct that things like contrast in picture styles should be decided first before setting the threshold in zebras settings.

Also, I just noticed I created this thread in wrong subforum; "general discussion / general chat" instead of "using Magic Lantern / general help Q&A". Feel free to move it if you wish.

[Audionut]

A calibration routine might help (point the camera to something overexposed, and recommend a threshold).

What about linking it to the calibration routine in mini_iso?

[a1ex]

The calibration for mini_iso only depends on raw data, while this one depends on picture style settings too.

I think I'll just print the maximum Y (luma) level in the zebra submenu, so if you have a light bulb or overexposed sky in the background while you adjust the threshold, you will get a good hint about the clipping point.