On Tue, 25 May 2004, Bernhard Praschinger wrote:
> > Would it make sense to have several 'regions' or 'bands' that have
> > different thresholds? If the majority of the frame has a Y' around
> > 20 +/-4 use a "-t 8", if it's centered about 28 +/- 4 then a "-t 6",
> > 32 +/-4 "-t 4", and so on...
> That sounds like a nice idea :)
Ah, ok - so it wasn't such a crazy idea after all.
> Are you planing to add that feature to yuvmedianfilter ?
No, although I will be "borrowing" some code from yuvmedianfilter. The
plan (and it's only in the thinking/idea stage now) is to create a new
program. If/when it becomes working code we can have a contest to
select a name for it ;)
> But if you make larger areas and goe than to the next level, it is more
> likely that you notice the "jump" to the next area.
True - conversations with a coworker raised the issue of "stair-step
effect" - it would basically be what can happen when -X and -Q are
used with mpeg2enc.
> From what I have read the human eye is able to determine
> black/gray/white much better than colors. You can fool the eye with only
Right - which is why we see the blocks/splotches in dark scenes. The
slight variations in Y' become more visible as the overall brightness
become lower. That's the reason I think averaging/smoothing more
heavily at the lower Y' values will be effective.
> > parameters to apply. What'd be great would be the ability to
> > "subtract" the differences between "pure black" and the "reference...
> Do you think the the area which you set to real black could be used for that ?
That's an area where there's no active signal usually - I don't think
using that would be a good thing. Now if there was a large portion
in the center of the reference frame.
I got the idea of 'subtraction' from an advertisement for a digital
camera (forget which one). Basically to subtract/cancel the CCD noise
the camera took a picture with the "lens cap on" (i.e. black) and then
computed the differences between that black picture and a theoretical
black frame from the real picture it takes a split second later.
I was thinking something like that might be possible with video data.
> I'll test anything that compiles on your machines ;)
Ok - don't hold your breath too long though ;) With that encouragement
I'll start planning the code Real Soon...
Cheers,
Steven Schultz
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