Black Shading -- Blacks Aren't Black.

[Kyle Mallory]

I'm hoping someone can shed a little light. I don't know if this is normal, or what, but...

It is my understanding that the black shading calibration calibrates the black from the sensor without any light, as being absolute black.

However, I've noticed that with the lens cap on, and the camera on, that my blacks are still not black. In fact, using build 16, they match the lowest gray bar next to black (but not black). All the menus and such appear as black-black, but the video frame is dark gray. I've also noticed, with the lens cap on, that the histogram show a peak about 5-8% up from the bottom, with a low-end falloff around 3-4%, and nothing registering below that.

I'm curious because this essentially means that I'm wasting a few bits of image space to stuff that the sensor can't detect anyway. Shouldn't the histogram be flat, with the lens cap on, just after performing a black-shading calibration?

Can someone (possibly from RED) confirm or clarify my findings?

 

[Stuart English]

Blacks

Blacks

What the sensor sees (and gets recorded) is different from what you are looking at via the monitor path, so don't worry about this...

 

[Deanan]

We don't clip the noise floor off so black is pure black. That can be bad in a number of ways including chopping off image info at the same time.

 

[Kyle Mallory]

Stewart, I figured that might be the case, and so I switched to the REDRAW view (build 16), and noticed it was still the same.

It first I thought along the lines of what Deanan said (chopping off image info), but as I thought more about it, it seemed contradictory, since anything below the noise floor of the CCD is still "black".

Anyway, my ultimate concern was that there might have been a bug in 16 with the black shading not performing correctly, but it sounds like this is normal behavior.

Thanks guys!

 

[Uli Plank]

This is normal behaviour. Black shading is about making all photosites see the same level of light, not about making the image pitch black.

Red is leaving the decision to us what we consider useable info and what is pure noise and can be discarded in post.

Regards,

Uli

 

[Graeme Nattress]

Absolutely correct Uli!

 

[Kevin Lang]

This is normal behaviour. Black shading is about making all photosites see the same level of light, not about making the image pitch black.

Red is leaving the decision to us what we consider useable info and what is pure noise and can be discarded in post.

Regards,

Uli

Thank you for that, I was curious about this because all this talk about how the camera was less noisy I did not find that to be true. This clears up that question.

 

[Kyle Mallory]

Yes, that makes perfect sense. Thanks.