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It's a really weird place to use JP2K -- they're functionally not space limited, or compute limited, so what's the advantage of wavelets? You could just gzip V2

by jfb 13y ago

It's a really weird place to use JP2K -- they're functionally not space limited, or compute limited, so what's the advantage of wavelets? You could just gzip V210 or something.

mark-r 13y ago
According to Wikipedia they squeeze 36 bits/pixel down to 4.71 bits/pixel for a 2K 24FPS movie. That's over 7x - gzip would be hard pressed to get up to 2x. I'm sure part of the reason they need compression is to send the data over the wire rather than shipping physical media all the time. [1] http://en.wikipedia.org/wiki/Digital_Cinema_Initiatives#Image_and_audio_capability_overview http://en.wikipedia.org/wiki/Digital_Cinema_Initiatives#Imag...
- yuhong 13y ago
  I believe that typically DCP movies are delivered via hard drive or satellite.
  - e12e 13y ago
    One of the benefits is that ingestion is flexible -- In general movies can be distributed via broadband (well in advance of release too, as the files are unplayable without decryption keys). For stuff like film festivals there's usually crates and crates of HDs :-)
    - jfb 13y ago
      This is why bandwidth isn't really a gating concern -- it's a mastered, offline format, so you don't need to squeeze all the possible bits out of the final package.
cjensen 13y ago
As mark-r says, it's about bandwidth. The movies are not hand-carried to each theater. JP2K is still the leader in visual quality per byte. All DCT-based compression systems (jpeg, mpeg, dv, etc) are prone to "mosquito noise" artifacts which are extremely annoying in moving pictures since the noise moves around and looks like mosquitos flying about. The usual workaround for mosquitos is to blur the picture a bit to make it easier to compress; but that softens the edges of object onscreen. Wavelet systems like jp2 suffer from different, less annoying, artifacts. gzip'ing 4:2:2 is a terrible idea :-). Keep in mind that Jp2K does have a lossless mode which you can use if you really don't want to lose any quality.
sjwright 13y ago
The spec allows for 4K (4096x2160 at 24 FPS) or 2K (2048x1080 at 24 or 48 FPS) source material and projectors. The spec recognizes that 2K sources may be played on 4K projectors (where it leaves the task of upscaling to the implementer) and 4K sources on 2K projectors. The advantage of the wavelet format is that they can implement progressive resolution decoding, so a decoder only needs to read half of the data from a 4K source to decode a full quality 2K image.
- jfb 13y ago
  Interesting. I had known about the mosquito noise problem (as cjensen notes (and I was joking about gziping 10-bit 422)), but I didn't realize the progressive decoding was a part of the standard. I spent some time in the guts of the DCP in a previous life, and software decoding of JP2K was always a nightmare. So I'm a bit jaundiced. But, as always, when you think an engineering decision is insane, you're probably missing the context in which the decision was made.

by jfb 13y ago

It's a really weird place to use JP2K -- they're functionally not space limited, or compute limited, so what's the advantage of wavelets? You could just gzip V210 or something.

mark-r 13y ago

According to Wikipedia they squeeze 36 bits/pixel down to 4.71 bits/pixel for a 2K 24FPS movie. That's over 7x - gzip would be hard pressed to get up to 2x. I'm sure part of the reason they need compression is to send the data over the wire rather than shipping physical media all the time. [1] http://en.wikipedia.org/wiki/Digital_Cinema_Initiatives#Image_and_audio_capability_overview http://en.wikipedia.org/wiki/Digital_Cinema_Initiatives#Imag...

yuhong 13y ago
I believe that typically DCP movies are delivered via hard drive or satellite.
- e12e 13y ago
  One of the benefits is that ingestion is flexible -- In general movies can be distributed via broadband (well in advance of release too, as the files are unplayable without decryption keys). For stuff like film festivals there's usually crates and crates of HDs :-)
  - jfb 13y ago
    This is why bandwidth isn't really a gating concern -- it's a mastered, offline format, so you don't need to squeeze all the possible bits out of the final package.

cjensen 13y ago

As mark-r says, it's about bandwidth. The movies are not hand-carried to each theater. JP2K is still the leader in visual quality per byte. All DCT-based compression systems (jpeg, mpeg, dv, etc) are prone to "mosquito noise" artifacts which are extremely annoying in moving pictures since the noise moves around and looks like mosquitos flying about. The usual workaround for mosquitos is to blur the picture a bit to make it easier to compress; but that softens the edges of object onscreen. Wavelet systems like jp2 suffer from different, less annoying, artifacts. gzip'ing 4:2:2 is a terrible idea :-). Keep in mind that Jp2K does have a lossless mode which you can use if you really don't want to lose any quality.

sjwright 13y ago

The spec allows for 4K (4096x2160 at 24 FPS) or 2K (2048x1080 at 24 or 48 FPS) source material and projectors. The spec recognizes that 2K sources may be played on 4K projectors (where it leaves the task of upscaling to the implementer) and 4K sources on 2K projectors. The advantage of the wavelet format is that they can implement progressive resolution decoding, so a decoder only needs to read half of the data from a 4K source to decode a full quality 2K image.

jfb 13y ago
Interesting. I had known about the mosquito noise problem (as cjensen notes (and I was joking about gziping 10-bit 422)), but I didn't realize the progressive decoding was a part of the standard. I spent some time in the guts of the DCP in a previous life, and software decoding of JP2K was always a nightmare. So I'm a bit jaundiced. But, as always, when you think an engineering decision is insane, you're probably missing the context in which the decision was made.