Disabling comb filter in EZCap device? - Page 1
Forum section: electronics / projects

author: Ben321
author_rank: Frequent Contributor
timestamp: February 05, 2017, 05:30:59 am
content: I have a Watec high sensitivity monochrome CCD camera. I'm getting video from it into my PC using an EZCap (or more likely a Chinese knockoff of the EZCap, since I bought it on ebay, and its logo doesn't quite look like the official logo). The thing is that in order to remove chroma carrier artifacts in the video (when the video source is color) it implements a comb filter. This creates a copy of the video signal shifted by about 2 pixels (the 1/2 wavelength of the chroma carrier waveform), and added back in to the main signal. This has the effect of canceling out the chroma carrier and any multiples of that frequency (it looks like a comb has raked through the spectrum graph when the signal is graphed in frequency domain, hence the name "comb filter"). However, this presents a problem.Because it shifts and adds the image onto itself, this produces a double image. This isn't noticable in most things, but it's particularly noticeable with my light sensitive camera as the signal source, as when it operates in the dark, you can see hot-pixels. And when the EZCap uses its comb filter, every hot pixel is doubled (there's a copy of each hot pixel about 2 pixels to the right). This may be necessary with a composite color image to get rid of the chroma carrier in the the luma signal, but my source is monochrome, and as such does not use a chroma carrier (something that should be detected by the capture device, and automatically disable the comb filter). In fact, not only is it not needed here (monocrome image), but because I intend to use it for scientific use, any artifacts like horizontal doubling of the image, is actually bad. That would taint any data acquired by the camera for scientific use. And there is no way to remove this pixel doubling. This artifact introduced by the comb filter can't be removed. This comb filter is a destructive/irreversable image processing step that is being performed by the EZCap, and that means that there is no way to remove it (just like JPEG artifacts in a JPEG compressed image).The only 2 possibilities for me are:1) Buy a more expensive video capture device that actually disables the comb filter for monocrome video (or allows one to manually disable the comb filter).2) Bypass the comb filter in the EZCap USB dongle by cutting tracings and soldering wires, as needed, to get the video signal to skip the chip that performs the comb filter processing step.I would like help with the second option. I'm considering modifying my EZCap, to bypass the comb filter. If anybody here on this forum knows how to bypass the comb filter in an EZCap, please provide me the modification instructions as a reply to this thread. Thanks in advance.

author: amyk
author_rank: Super Contributor
timestamp: February 05, 2017, 06:58:29 am
content: You may want to open it up and see what ICs it has first. I doubt the comb filter is a separate IC, or that it is configurable via pins on it, but is more likely to be configurable in software.

author: Ben321
author_rank: Frequent Contributor
timestamp: February 05, 2017, 07:08:58 am
content: Quote from: amyk on February 05, 2017, 06:58:29 amThere is no feature in the driver that allows the comb filter to be disabled.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 05, 2017, 07:19:13 am
content: Connect the camera to the Svideo input. Leave the chroma signal unconnected or terminate it to ground.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 05, 2017, 10:05:06 am
content: IIRC, color devices are supposed to disable the chroma hardware when a B&W signal is detected -- or rather, when no color burst is detected. This has been in the standard since the first days: some vacuum tubes carry the suggested use "color killer", for implementing this disable function.Unfortunately, it would seem this manufacturer forgot to.S-Video is a good idea though. That should tap into the signal path after the filter.Tim

author: amyk
author_rank: Super Contributor
timestamp: February 06, 2017, 01:18:07 am
content: Quote from: Ben321 on February 05, 2017, 07:08:58 amThe driver doesn't always reflect the capabilities of the IC in the device. But if you can at least get the PID/VID and look it up, you may be able to find a datasheet for it.

author: cdev
author_rank: Super Contributor
timestamp: February 06, 2017, 03:02:06 am
content: Have you tried running it under Linux?

author: Ben321
author_rank: Frequent Contributor
timestamp: February 06, 2017, 05:21:25 am
content: Quote from: NiHaoMike on February 05, 2017, 07:19:13 amQuote from: T3sl4co1l on February 05, 2017, 10:05:06 amI tried S-Video, and still it does the exact same thing. It seems that ALL video signals coming into the device, no matter what, go through the comb filter. As I said in my opening post, I think it may be a cheap Chinese knockoff. I'm not sure what a real EZCap would do (or other video capture devices like the Hauppauge device herehttp://www.hauppauge.com/site/products/data_usblive2.html) when it comes to processing monochrome video through the Composite or S-Video inputs, as I don't have any of the more expensive ones (that are more likely legit). This one I got this from eBay, because it was cheap. I don't have any actual brand-name video capture devices, that I can be 100% sure are legit, to compare it to. I usually buy stuff on eBay because it's cheap, but there's no guaranty that it's not a knockoff.So maybe the question I should be asking is this. With the EZCap devices, which is the most common ACTUAL hardware inside of one of these (not the hardware it advertises itself as, such as EZCap)? And how do you bypass the comb filter in such a device.

author: cdev
author_rank: Super Contributor
timestamp: February 07, 2017, 01:17:18 am
content: I think the device is an skc 60 (from memory)