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08-05-2018, 06:41 PM
ehbowen ehbowen is offline
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This is a problem I hadn't run into before now. While doing a re-capture of King Of Thieves with my Mitsubishi HS-HD2000U >> TBC-1000 >> AIW 8500 workflow, I noticed a couple of segments (not very many) which were "washed out"...excessively white. This is just a personal practice project, but I'd like to know how to correct and prevent them in future if at all possible. The capture proceeded normally with no dropped frames, but I saw these on playback. I wasn't able to monitor the capture because my display goes all to hash if I set VirtualDub at any setting other than 640 x 480. I tried using the Microsoft VDM device for capture as Lordsmurf suggested in another post, but then I had even worse "washout" results...about 40-50% of the captured video was like these samples when capturing from the Microsoft device (and the same portions of the tape, too); only about 5% when using the ATI device setting. However, my earlier capture made last week looks to be clean although I haven't gone through it in detail.

After Sanlyn took me to task, I double-checked my VirtualDub capture settings. I did have it set to capture in YUY2 720 x 480. However, the defaults on the program on the computer I was using to save the earlier clips were set to save in RGB. I'd like to determine for-sure what the earlier capture was saved as but I don't know of a utility for doing that with certainty and a Google search was unproductive (maybe because I don't know what to search for?). So advice is welcomed.

Edit To Add: Okay, the "clip 1" is all right; I think I botched the clip selection. But clips 2 and 3 show what I'm talking about.


Attached Files
File Type: avi KingOfThieves.clip1.20180805a.avi (95.70 MB, 13 downloads)
File Type: avi KingOfThieves.clip2.20180805a.avi (72.19 MB, 5 downloads)
File Type: avi KingOfThieves.clip3.20180805a.avi (51.43 MB, 5 downloads)
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  #2  
08-06-2018, 06:12 AM
sanlyn sanlyn is offline
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Your samples don't have frames that are "washed out". They're distorted beyond repair.

There are also some oddities about the luminance levels, as shown below. The right-hand part of the image below is a YUV histogram of the frame. This is Avisynth's "Levels" histogram, which should be familiar since you've probably used it numerous times (!). In the upper right-hand corner I have superimposed a white arrow that points to the right-hand edge of the white luminance band, which is clipped (sharply terminated) at precisely y=235. Otherwise I have absolutely no idea why this group of frames is so badly distorted.


Below, the frame is otherwise normal but note that the histogram shows exactly the same clipping limit at y-235. Under normal circumstances the capture would clip at y-255, not exactly y=235 on every frame. And since YUV can contain values greater than 255, YUV clipping shouldn't be evident on any of these frames.



The way to prevent YUV->RGB conversions when making these smples or doing otehr processing is to open a YUV video in VirtuaLDub and make your desired cuts band edits for a sample. Then click "Video..." -> "direct stream copy" before saving the sample. This copies the original incoming colorspace. Saving your sample using "full processing mode" automatically converts the video to RGB, even if you set other colorspaces or compressors for output.


Attached Images
File Type: jpg luma limiter 2.jpg (82.5 KB, 18 downloads)
File Type: jpg luma limiter 1.jpg (68.5 KB, 18 downloads)
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  #3  
08-06-2018, 06:40 AM
ehbowen ehbowen is offline
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Yeah, I'm not trying to salvage that capture as much as I am trying to prevent the problem from recurring. I was thinking that it might be a cabling issue going in to the capture card or similar, but I haven't been able to find the weak link in the chain just yet. Just hoping that someone else had run into the same problem and could give some suggestions.

Where's the best documentation on learning to use Avisynth?

Last edited by ehbowen; 08-06-2018 at 06:41 AM. Reason: Add first sentence.
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  #4  
08-06-2018, 07:05 AM
sanlyn sanlyn is offline
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Quote:
Originally Posted by ehbowen View Post
Where's the best documentation on learning to use Avisynth?
There is no complete, one-stop-shopping document that tells you how to use Avisynth. The main reasons are that there are dozens of Avisynth plugins and thousands of functions, all of which can be used in hundreds of ways on millions of different video problems. It would take quite a tome to cover that much territory.

However, there's a simplified how-to on the basics of writing Avisynth text scripts. It exists in the online help that is accessed in Windows by opening your program listings, finding the "Avisynth" program group and expanding it, then click on "Avisynth documentation". The online help itself is located in the Avisynth program folder.

Most people learn Avisynth by following forum posts. Usually you'll find the same methods used over and over, since so many problems are common to VHS. You also learn by doing what you've just done, which is submitting samples and questions. You don't always get a solution (obviously, playback problems aren't Avisynth's fault), but with video cleanup you usually get several answers.

[EDIT Sorry, I clicked"Submit" too soon, LOL!]
There is considerable documentation available with the more popular and well-developed Avisynth plugins, as well as hundreds of online articles in the Avisynth wiki (just enter something like "Avisynth Crop" in Google and see what you get). Some of the docs get fairly high-tech -- you don't have to understand all of it, just getting the general idea is usually enough. Often there are examples of how the filter is used in scripts.
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