ATI 600 USB: histogram gaps, sharpness settings?
 

Hi,

I am trying to find the best proc amp settings for my ATI TV Wonder HD 600 USB Digital & Analog TV Tuner when capturing PAL VHS in VirtualDub.

My current chain is:

JVC HR-S7600 VCR → DataVideo TBC-1000 → ATI TV Wonder HD 600 USB → VirtualDub 1.9.11 → YUY2 / Lagarith lossless AVI

I am using PAL 720×576, 25 fps, YUY2.

I have been testing the ATI proc amp settings using the static menu screen from my JVC VCR. This gives a very useful test image because it has a blue background, white text, black borders and sharp high-contrast edges.

I am attaching three screenshots from VirtualDub capture mode with histogram visible (please see the attached zip file for originals):

1. ATI default settings:
Attachment 20566

2. Brightness increased:
Attachment 20567

3. Brightness increased, sharpness disabled:
Attachment 20568

What confuses me is this:
With sharpness 2, the histogram looks smoother and there are no obvious gaps. However, visually the image looks artificially sharpened. Around the white text and menu graphics I can clearly see harder edges / edge enhancement. Also, when brightness is raised to 118, there is some red on the right side of the histogram, which I assume may be overshoot from the sharpening around the white text.

With sharpness 0, the image looks much more natural to my eyes. It also matches my DVD recorder and Diamond VC500 captures better in terms of natural edge appearance. The red on the right side of the histogram mostly disappears. However, obvious “gaps” appear in the VirtualDub histogram.

So I am trying to understand what is the lesser evil here.

My questions are:

1. Are the histogram gaps at sharpness 0 a serious problem, or just a quirk of the ATI driver/proc amp processing?
2. Could these gaps cause visible banding/posterization later during color correction?
3. If sharpness 1 and 2 both look visibly over-sharpened, would it still be better to use sharpness 0 even though the histogram looks worse?
4. Is the red on the right side with sharpness 2 likely caused by sharpening overshoot around the white menu text?
5. For archival captures, would you prioritize the more natural-looking sharpness 0 image, or the smoother histogram at sharpness 2?

I normally make two captures in parallel: one DVD recorder capture for easy viewing, and one ATI 600 lossless capture as an archival file for possible later restoration/color matching. So the ATI file does not need to look “finished” straight out of the box. I mainly want to preserve as much usable image information as possible without baking in artificial processing.

At the moment I am leaning toward something like:

Brightness 116–120
Contrast 32
Hue 64
Saturation 32
Sharpness 0

But the histogram gaps make me unsure :unsure:

Any advice would be greatly appreciated.

Using post-capture digital adjustments is pure evil.
On a side note. Picture control in your VCR menu has to be set to Edit.

The VCR's menu is electronically generated and isn't going to contain all the colors of the rainbow. The character generator chip probably only has 8 or 16 colors in its palette.

I think my point may have been misunderstood.

I am not trying to “improve” the image with random digital adjustments. I am trying to avoid the ATI 600 baking artificial sharpening into the capture. At default sharpness 2, the card clearly adds edge enhancement around the white menu text. Setting sharpness to 0 removes that and looks much more natural, but then VirtualDub shows histogram gaps.

So the question is not “should I adjust the image after capture?” The question is: what should I do when the capture device itself appears to add unwanted sharpening at its default setting?

The JVC menu is only used as a repeatable static test image. I know it has a limited generated palette. That is not the point. It is useful here because the white text on blue background makes the ATI edge enhancement easy to see.

On normal tape material I also see sharpness 1 and 2 as artificially enhanced compared to sharpness 0, but the menu screen makes it easier to demonstrate in screenshots.

So my main question remains:

Would you choose sharpness 0 for a more natural-looking capture despite the histogram gaps, or sharpness 1/2 for a smoother histogram despite visible edge enhancement?

I would say use card's default. However, that doesn't guarantee the minimal distortion.

You do pose a very difficult question, something's got to give here. :) Ultimately, it will be your personal preference that will decide.

If you haven't seen this, this forum post https://www.digitalfaq.com/forum/vid...histogram.html may help.

I used to use an ATI 600 USB clone (Tevion), and I recall seeing virtualdub histogram "spikes" going up, instead of down, when I adjusted contrast in the Levels menu. When I looked at the histogram of the captured video in AviSynth, I saw the same spikes, so I knew it wasn't a Virtualdub glitch, it really was modifying the luminance histogram of the capture. I don't recall the Sharpness giving me issues, but it's been too long ago to remember. Perhaps I just left it a default, or the Tevion didn't have this problem.

Once I switched to an ATI capture card, I never saw those spikes again no matter what I did with Levels. I think the difference had to do with the capture card having an internal proc amp, were as the USB did not. So, that left me with the impression that the spikes are certainly not native to the video source or output of the video equipment, and so my first impression would be to avoid anything that is modifying the video luminance data in that way.

Perhaps the histogram can be fixed in something like Avisynth with the Levels command and specifying dither=true. But I cannot recall, just an idea to try. But, at least theoretically, I'm not sure I'd want to have the histogram altered by hardware, then have to alter it back again in software.

Although, there are other kinds of Avisynth/software filters one might use to achieve similar means of reducing the sharpness/haloing/etc. Of course, that would take more time and research.

Best of luck in your decision. This seems like a minor thing that should not consume excessive amounts of time focusing on. Whichever pros are better to you than the cons is where you will likely go.