Recovering blown highlights

[Mr Chris]

I've been sent a video with badly blown highlights (not my capture, tape long gone, unfortunately), and I'm trying to fix it up the best I can, but I'm not really getting anywhere with my usual methods. I accept that a lot of detail is gone forever, but what are my best options for at the very least improving matters?

I've attached some screenshots and a representative sample from the much longer video - what techniques would you use to get it the best it can possibly be from such an iffy source?


[Attachment 79465 - Click to enlarge]

[Attachment 79467 - Click to enlarge]

[Attachment 79468 - Click to enlarge]

Just as an added aside, what could cause the highlights to blow so badly? I'm pretty sure this is straight from a DVD recorder and hasn't been processed. The chroma looks okay, but the luma seems to have rocketed off the scale. I'm just trying to understand what went wrong in the first place.

[Sharc]

Just as an added aside, what could cause the highlights to blow so badly?

- Improper Proc-amp or video levels settings during capture
- Wrong level conversion (expansion) applied, like limited (TV) to full range (PC)
- Poor capture device
- Something wrong with the DVD recorder (unlikely)
- Improper camera settings (problem would have been baked onto the tape)
- a combination of above ....

There is no way in recovering clipped brights. Maybe a little improvement by tweaking the levels (Avisynth, NLE or similar) should be doable.

[jagabo]

You can pull a little detail out of the brights. Here I've done so with AviSynth:

LWLibavVideoSource("sample.mpg") 
StackHorizontal(last, ColorYUV(gain_y=-20, off_y=-4))
TurnRight().Histogram().TurnLeft()

[Attachment 79471 - Click to enlarge]

The snow isn't completely blown out so you get a little more detail there. But in the kitchen scene the door is completely blown out so there's still no detail there. You can see a little more detail in other bright parts of the picture. Like the plate in the lower left corner:


[Attachment 79473 - Click to enlarge]

Any program that lets you adjust levels in YUV should let you do this.

[Mr Chris]

Thank you both very much.

You can pull a little detail out of the brights. Here I've done so with AviSynth:

That's a lot more detail than I was managing to get out of the brights in Premiere, so that's encouraging. A definite improvement - thanks.

[taigi]

@jagabo Great results. Would these settings be universally applicable to DV footage as well?

[timtape]

With the medium close woman shot, one way to shoot it would be to set up a light to make the woman brighter. But failing that, at least manually expose for the woman even if it meant blowing out the bright background, which is probably what was done here. Sometimes we have to look at the picture and decide which part of the picture is the most important such as the woman in this shot. If other parts of the shot are over/underexposed, that's the tradeoff we sometimes have to make.

[poisondeathray]

Would these settings be universally applicable to DV footage as well?

It would only be applicable if you have usable data in the "superbright" Y 235-255 region. If your footage is so overexposed , clipped and blown out that there is no usable data, it won't work

It cost you nothing to test it, except maybe 1 minute of your time

[taigi]

What about HDRAGC in this case? Retinex?

[Sharc]

What about HDRAGC in this case?

HDRAGC is 32bit only.
Why don't you try yourself and report your findings? Each case is unique. Use avisynth's histogram and waveform monitor to check the effect.
DV often have data in the 235...255 range which will be lost upon standard (Rec601, avisynth, many NLEs) YUV->RGB conversion unless you set the levels right beforehand. But as has been said clipped video data cannot be recovered. Lost is lost. There is no wonderware or universal solution.

Retinex: Can help to recover details from (underexposed) darks. From the clip in post#1:

[Attachment 84175 - Click to enlarge]

[taigi]

Reporting: using the 64-bit version of Retinex, along with a mask to isolate highlighted areas, I'm getting decent results. It's rendering now; I don't yet know what the very final results will be.