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ticking artifacts on SD channels |
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#1 |
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Forum Member
Join Date: Jun 2003
Location: Staffs, UK
Posts: 28
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ticking artifacts on SD channels
I quite often notice that static pictures with intricate detail suffer from a regular (about once per second) cycle where the detail goes fuzzy, then back to really clear.
It's a bit like what happens when a progressive jpeg is loading - sort of grainy on the details that then gets progressively better before the whole cycle starts again. I suspect that it happens most of the time, it's just not as obvious unless the picture is static and detailed. This is with a humax foxsat hdr, and I see it most on BBC4 with the arty programmes, but I've seen it on most other channels as well. I'm using a 100" FP screen (Sanyo Z5). Is this artifacts in the transmission stream, or problems with the humax, or with the projector? |
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#2 |
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Guest
Join Date: Apr 2004
Posts: 957
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Yep, that's the way MPEG works.
Every so often you get an I-Frame that is the complete image. This is then followed by P & B frames that update this image. The interval between I-Frames is up to the encoder. If you have x bits-per-second channel capacity then the I-Frame must fit in x/50 bits (on PAL) and this is effectively a JPEG image. The following P & B Frames also get x/50 bits to update the image to reflect how it has changed. With a static image this capacity can instead be used to provide additional detail which is what you are seeing. |
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#3 |
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Forum Member
Join Date: Jun 2003
Location: Staffs, UK
Posts: 28
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Quote:
Yep, that's the way MPEG works.
Every so often you get an I-Frame that is the complete image. This is then followed by P & B frames that update this image. The interval between I-Frames is up to the encoder. If you have x bits-per-second channel capacity then the I-Frame must fit in x/50 bits (on PAL) and this is effectively a JPEG image. The following P & B Frames also get x/50 bits to update the image to reflect how it has changed. With a static image this capacity can instead be used to provide additional detail which is what you are seeing. |
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