When "Clipped" Highlights are Not Really Clipped

basspig

basspig

Veteran
I shot a parade not long ago, and was analyzing some of the frames, observing the exposure levels.

I noted that some of the footage appeared 'overexposed' in the NLE (Premiere CS3). So I experimented with several video effects filters and found that the Fast Color Corrector would allow me to compress the upper range, rather than simply clip off the >100IRE levels.

The below images are the uncorrected and corrected images that were exported as a frame from Premiere. You'll notice that even though the footage looked overexposed, there actually is detail up there above 100IRE, though the NLE couldn't display it. I simply brought it down (and Premiere was able to process it) until the details in the white tunics and feathers were restored. The XDCam actually recorded those details, but in my initial edit, I simply assumed those details were clipped in the camera. They were not. Just thought I'd share that. :)

picture.php

UNCORRECTED


picture.php

CORRECTED RECOVERED HIGHLIGHT DETAILS

If the pictures above don't appear, try this link to my album with these examples:

http://www.dvxuser.com/V6/album.php?albumid=175
 
That would be purely speculation on my part, as I don't own FCP nor use it here. I can only speak about Premiere Pro CS3/4.


Another thing I found out is that Sony's Clip Browser ALSO clips the hilights. I queued up the same clip in SCB 2.5 and compared the adjusted clip in Premiere to the preview screen in SCB and could easily see that the whites were blown in Clip Browser, but not so in Premiere with the Levels adjustment. This suggests that Premiere is able to process information above 100IRE, but not display it or render it, without bringing the overall levels to <100IRE with Fast Color Corrector.

The difference is substantial, and the above reduced-sized images don't clearly show the difference as well as the full raster originals. It is quite dramatic. I found another shot where the sky was blown to white where the sun was, and after the Levels adjustment, I found there were patches of blue sky where the clouds break up. All that information was lost in the render when I didn't use the Levels tweak that I discovered yesterday!
 
Those blown out area might not actually be 100 IRE, but it will appear blown out just the same. Reducing the White Output values in the Fast Color corrector will bring it back if it's around 85 IRE or less, but I'm pretty sure if exposure hits 100 IRE, it's gone for good.

EDIT: I downloaded your still and dropped it into Premiere CS4. The highlight area you recovered is actually around 80 IRE, with a few clipped area. Messing around with the Fast CC recovered details in these areas but not the clipped highlight. The lower contrast simply gives an illusion of more details.
 
Last edited:
The blown areas were 109 IRE on the scope. That's how I knew how much to adjust down, to bring the whole image to just AT 100 IRE, on the scope. That is when I discovered detail that was completely flattened out before. Also, I discovered that the sky had some patches of blue, in another shot taken earlier when it was still somewhat overcast, once I lowered the peak values to 100 IRE. The sky was completely blown to white before I made the adjustment.

I also should note the EX1 was set to STD4 and -3dB gain. And it still produced 109 IRE whites.

Uploaded and board-software-manipulated images will probably NOT maintain the original spectral information, so I would not be confident in the numbers extracted from them.
 
hey Mark,
have you tried using any of the Cine Gammas for day exteriors? or do you prefer more of a video/punchy look. i read somewhere, either here or on the other forum, that someone posted the different clipping % for each Gamma setting; STD and Cine. i basically would like to know why you choose STD4 as a gamma setting and if you adjusted the KNEE at all.

thanks,
Mike
 
Mark,

Pro cameras usually record from 0 IRE to 109 IRE. The range from 101 to 109 IRE is called superwhite. Although this area is not broadcast "legal", it does give you a little extra room for safety.
 
I've played with the cine gammas, but I feel that they reduce the range of contrast recorded. As Sumfun points out, there are benefits to recording 0-109IRE, mainly, you capture a little extra contrast information. Compressing that down in post is better than discarding it in-camera, in my opinion.
That aside, cine gammas look a bit more dull, and I often get the sense that I'm not capturing the full range of the scene.
 
You must log in or register to reply here.
Back
Top