[FFmpeg-trac] #8590(undetermined:closed): 'telecine=pattern' error for p24, soft telecined sources

[FFmpeg]

#8590: 'telecine=pattern' error for p24, soft telecined sources
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             Reporter:  markfilipak  |                    Owner:
                 Type:  defect       |                   Status:  closed
             Priority:  normal       |                Component:
                                     |  undetermined
              Version:  unspecified  |               Resolution:  invalid
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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Comment (by pdr0):

 Replying to [comment:37 markfilipak]:
 >
 >
 > > It's aliasing artifacts, when viewed in motion. It boils down to
 undersampling.
 >
 > Well, undersampling should produce image fade (amplitude loss due to
 insufficent energy transfer), not aliasing.
 >

 It's undersampling in the most simple sense.  That is what interlace is:
 Spatial undersampling, but full temporal sampling. Each field has half the
 spatial information of a full progressive frame.  A straight line becomes
 jagged dotted line when deinterlaced, because that field is resized to a
 full sized frame and only 50% the line samples are present. That line
 information is undersampled.  In motion, those lines appear to "twitter".
 Higher quality deinterlacing algorithms attempt to adaptively fill in the
 gaps and smooth everything over, so it appears as if it was a true
 progressive frame.

 As motioned earlier, there are other causes, but low quality deinterlacing
 is the most common.  Other common ones are pixel binning or sampling every
 nth pixel. Eg. large sensor DSLR's when shooting video mode. Instead of a
 proper resize (with interpolation kernels), dropping pixels is performed.
 The image has gaps and is undersampled . These manifest as moire patterns
 and buzzing "twitterin" lines


 >
 > > Essentially gaps in information, which are more easily identified in
 things such as straight lines , and that's what twitter usually refers to
 (lines, edges).  In layman' s terms it looks likes jaggy buzzing lines.
 (Of course you can get "jaggy buzzing lines" from other things too, such
 as compression artifacts, but twitter has a characteristic look)
 >
 > I believe that, except for compression artifacts, what you describe is
 combing, which is a temporal artifact of the clash of interlaced field
 lines from differing sample frames/times.
 >

 Yes , combing is usually 2 fields are sampled from 2 different points in
 time. Interlace looks like this. Progressive field shifting as well. These
 are temporal issues.

 There are other causes, but it comes down to anything that causes
 misalignment of fields will manifest as combing eg. film warping when it
 was run through the scanner. This is actually a spatial problem. The field
 pairs actually come from the same point in time



 > >
 > > Yes, it's a synthetic high contrast test, but it's still predictive of
 the issues you see on real content. Real content will typically also have
 motion blur, so the effect can be reduced somewhat
 >
 > Well, motion blur is the human response to combing of motion objects,
 especially if smoothing is applied as most TVs apply smoothing. That's the
 first thing I turn off in TV setups. The second is "image enhancement"
 (i.e., sharpening and contrast enhancement or active contrast or motion
 enhancement, etc., whatever they call it). Basically, I flatten everything
 and desaturate the picture until it portrays scenes naturally, like in a
 movie theater. Then I put up a test picture and compare it with the
 photograph used to make the test picture and adjust gamma & RGB gain.
 >

 The motion blur being referred to here is the one applied by the camera
 shutter. Images caught on film or digital equivalent will have motion
 blur. The faster the shutter speed, the less the motion blur.

 This animation was made without motion blur on purpose (typically you add
 motion blur during or in post to animations) . The high contrast edges
 without blur serve to highlight various issues.

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Ticket URL: <https://trac.ffmpeg.org/ticket/8590#comment:38>
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