Quality of captured stills from analog video

[Sven]

Just some quick questions from a photographer's point of view:

* What's the maximum quality you can squeeze from a RR-G when you use it for still-image grabbing from analog video?

* Can you digitize higher resolutions than PAL?

* Can you turn off MJPEG compression for that purpose?

* Does anybody have some high-quality stills online to get a feeling for the quality?

Bye, Sven

[Grigory]

Hi,

If you capture still from PC VCR remote:
a)single field is taken from the frame, and interpolated to 640x480 size, or any other size. The true resolution is about 352x288 (PAL) or 352x240 (NTSC), anything else is a product of interpolation.
b) the R,G and B values change with steps of 4. This is not much visible, however, the image looks little strange in colors.

To get best possible resolution and colors, capture video in MJPEG and extract frames in video editor. You'll get 704x576 image (PAL) or 704x480 in NTSC. You can remove one field in image editor, if the frame contains motion. Resulting image will have true resolution of 704 x 288(240), resampled to correct aspect ratio 768x576(PAL, get your value for NTSC).

It is useless to try to get more pixels - the number of luma samples is 704 in line.

To decompress MJPEG with best possible quality, use morgan codec with floating point decompression. Or, change the video mode to 24 bit and take frame with Matrox software codec. It also has better quality (crispness). Hardware codec does not work in 24 bit color depth.
The quality of still picture depends strongly on your video source. Analog camcorders have a noise in color components. Still image can show this noise, especially for VHS source.
DV format stills look great. However, many DV camcorders use single field for in paused playback, thus reducing the vertical resolution. To get best image, take a frame from video captured in normal playback mode.


Grigory

[This message has been edited by Grigory (edited 10-04-1999).]

[Sven]

Gregory,

thanks a lot for the detailed info. I remember video hardware claiming to capture at very high resolutions, but now I see that would be way beyond the specs of PAL/NTSC - it will be smoothed by upsampling.

Regarding colour noise: Is the luma noisy with VHS (or Hi8) cameras, too? You could smooth out colour noise in the a* and b* channels in Photoshop Lab mode when needed without touching the luma components.

Other than that: It's video after all, perhaps the noise in stills is even an interesting artistic means of transporting the "video-ness" of the stills. Got to experiment.

For fast snapshots and rough web design, I might get away with the camera as a cheap subtitute for a digicam. If I want quality, I'd rather take my SLR.

Bye, Sven

[Keith Wiebe]

Thanks for the tip Grigory! I just got my Sony digital 8 camera and was dissappointed by the still capture method on the RR remote. I inserted an avi file into video paint that was made at 2.5mbs and created a still image file at 100percent quality under options and was pleasantly surprised by the qualtiy. I did have some color casts caused by mixed lighting at the time and the quality of the single ccd chip causes some yellowing at times but the qualtiy is great for web pages, etc. The file size is 254kb vs 34kb for the remote capture utility. I can e-mail this picture to someone if they want. keithw@southwind.net

[Grigory]

There was a long post some time ago considering the quality of RR_G uncompressed and still image captures.
That time I was told how bad am I understanding the RR_G intention for only mjpeg movie captures. Well, I took the point that mjpeg is the only one format that has reasonable quality in RR_G.

I also have digital8 camcorder and used this technique for stills every time before moving to DV-only with Raptor.

Sometimes the manufacturers like Sony try to simplify everything. In the case of D8 camcorder stills, they decided to discard one field to escape flickering. BTW, DV card is able to switch the camcorder to show stills with either field or both. Unfortunately, camcorder cannot remember the settings. So, you cannot take it to a friend with DV card and switch to full frame stills.

Considering noise, I think that horizontal colored still lines are not very good for any effect. However, it depends on what you need to get. For internet you can try to capture still several times and get several noise patterns. Then, make animated GIF and you'll have very good TV-style banner.

I tried to filter chroma components to reduce noise. The image looks colored even if you apply Gaussian filter up to 10 or 15 in value to chroma components only. The only noticeable place were white area of eyes on human face, which became colored as face itself. Apart from this, the image was looking crisp and noise-free.

Grigory