[opendtv] Re: De-interlacing with HQV high quality video processing
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Thu, 6 Oct 2005 08:08:18 -0400
At 11:24 AM -0700 10/5/05, dgrimes@xxxxxxxxxxxxxxxxx wrote:
>While I find interlacing reprehensible, since there are interlaced formats
>that need to be displayed, couldn't displays be designed to display
>appropriate pixels at the appropriate time? Seems to me that it is just a
>matter of clocking in the right pixels at the right time, allowing a
>progressive or interlaced image to be displayed natively. I am sure I am
>showing my lack of knowledge in the architecture of bussing bits in the
>current display technologies. But it seems like something could be
>designed that way. Of course, it doesn't account for the different
>resolutions.
Interlace works because it takes advantage of the human visual system
to fill in the gaps from undersampling. Remember, with a CRT, the eye
is not seeing complete pictures, it is seeing a moving spot of light.
The integration takes place in the brain, which allows us to see
coherent images. Also, a properly designed interlaced display will
use a spot size that is roughly equivalent to two video lines in
height; Thus each field is "painted' as a complete picture at 1/2 the
resolution for a given number of lines.
IF you display the entire video field - with gaps between lines - the
magic that takes place in the brain no longer works. Rather than
seeing a moving spot of light, the eye sees the entire field,
including gaps, and the whole illusion falls apart. Thus for ANY
display technology where the entire image is displayed for the field
or frame period, you must de-interlace the image and display it as a
progressive frame, or you will see all kinds of artifacts that are
not visible with an interlaced scanning display.
There is one display technology that has tried to combine the best of
both. That is a p[lasma panel that displays interlaced fields by
deflecting the samples onto alternative surfaces of the tubes used to
create the pixels. For the first field the samples are displayed
slight up, the next slightly down. I am not certain if the panel is
scanned when this is happening or if the entire field is displayed
for the field period. And I am not certain of any company is still
making panels that use this technique. I have not been impressed in
the demos I have seen.
The ideal display system presents the entire frame for the frame
period. Jeroen may jump in an tell us about techniques that blank the
screen between frames to enhance the perception of sharpness.
Regards
Craig
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