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-   -   Adjust Brightness/Contrast for Multiple Scenes (http://www.digitalfaq.com/forum/video-capture/10903-adjust-brightness-contrast.html)

Okiba 08-17-2020 03:58 AM

Adjust Brightness/Contrast for Multiple Scenes
 
Hello again everyone! Hope you all feeling good and in good health :-)

I (finally) started the process of capturing 82 (!!!!) VHS-C tapes. All those tapes are events from family history, taken with the same Video Camera. It was taken by my father, and his not a professional Camera man. So in the topic context, he never tweaked WB settings on the Camera, and I already encountered a footage where everything is too dark because of the extremely white background (snow). Each VHS-C tape includes couple of events. Some are filmed in daylight, some in a dark house.

On the VirtualDub guide it was mentioned that after cropping the Noise/Black section - it's a good idea to use the Histogram to tweak brightness/contrast (By the way, Preview won't show anything when Histogram is on for some reason). But as I mentioned, some events are bright, and some are not. I can't be sure if the event I'm currently watching (the one at the start of the tape) is the brightest, or the darkest of this specific tape - and it's of-course impossible to watch all the tape, pick the brightest/darkest moments and to tweak brightness/contrast based on those. It will take to much time.

So I wonder, what's the proper way to tackle that? Just pick the first scene on the tape and adjust based on that hoping for good?

Also, I have couple of questions regarding the process of tweaking brightness/contrast:

1. Let's say I'm watching a scene that is not too dark, nor too white - and the Histrogram "Blue" section is somewhere in the middle, I can use the brightness/contrast to "stretch" the blue section to a point where it closet as possible to 16-235 without reaching the red zone. Will this "Fix" any badly lighted scene? or just make things worse? As a rule of a thumb - should I avoiding "Extending" the blue section and instead only decrease it when I see actually clipping?

2. The 2-3 tapes I tested, had a very similar values of brightness/contrast at the end. So if In VirtualDub the middle value for brightness/contrast is 5000, the lowest is 0 and the highest is 10,000 - With VC500, I add around 1500ish to the Brightness (so 6000-6500) and the contrast is lowered by around 500 (so 4500-4000). Will this value always be the same on all captures because I'm using the same Capture card and the footage was taken with the same Video Camera (on default settings)? or this is based on the scene lighting?

I'm assuming there's a way to play with brightness/contrast post capture, but information lost during capture because clipping, is lost forever I'm guessing.

Thank you!

Okiba 08-18-2020 02:42 AM

I found this post by keaton. It was mentioned there that:

Quote:

Don't worry about getting things maxed out necessarily. You can fix it later in post
So I assume there was nothing wrong with me "stretching" the histogram on those tests I did. It means that while a scene might be too bright due to stretching - It's something I can fix post-processing. The only problem if that something clips, because then I really lost that detail forever.

That being said, It seems like a good rule of a thumb is to only fiddle with brightness/contrast if your clipping. Maxing out the Histogram might cause problem on later brigher/darker scenes.

So that's 1 question answered :)

traal 08-19-2020 01:22 PM

My suggestion:

1. Find a scene on one tape that's really dark, and set brightness high enough that the blacks aren't crushed.

2. Then find a scene on that tape or another one that's really bright, and set contrast low enough to eliminate clipping.

3. Remember both settings, and use them for all your tapes.

4. If you change the VCR or capture card or anything in-between, or want to capture tapes that were recorded by a different camcorder, recheck and determine your new brightness and contrast settings.

Okiba 08-19-2020 03:15 PM

Thank you traal. So you suggests that brightness/contrast tweaking is per setup. That's sounds like a good plan. I wonder if I should re-capture the 3-4 tapes I already captures for the sake of it. I think I did the "Stretch" method I describe above. Nothing clipped, but I might have pumped brightness too much on dark-to-be scenes.


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