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aous72 avatar aous72 commented on June 4, 2024

Pcap is 32 bits. Whenever a Pcap bit is set, a corresponding Ccap field shall be included in the CAP header; Ccap is 16 bits.

Pcap bits are counted from the most significant bit; perhaps, this is due to the big-endianness. For HTJ2K, Pcap^15 should be set. Perhaps the comment can be improved by saying "for jph, Pcap^15 must be set; the 15th MSB bit." I know this might seem weird, but this is how it is.

Cheers,
Aous

from openjph.

boxerab avatar boxerab commented on June 4, 2024

Thanks, Aous. Yes, it is weird :) It's not clear from the standard that this is the case, and I couldn't find where it specifies that Pcap is 32 bits. Thanks for clarifying this :)

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boxerab avatar boxerab commented on June 4, 2024

Actually, I still don't think this is correct :) Even if it is big endian, the 15th MSB bit set should be
0x00008000 rather than 0x00020000 which is the 17th MSB.

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aous72 avatar aous72 commented on June 4, 2024

Pcap is not in the original Part 1. It was added later. It is in the latest edition of Part 1.

The attached picture should make it clear; Pcap15 indicates JPH -- Perhaps describing it as 15th MSB is still not very clear.
Screen Shot 2019-12-27 at 11 28 58 am

It is weird because it is counted from the MSB, and because it starts with 1, not 0.
Cheers,
Aous.

Edit: corrected "addition" to "edition"

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boxerab avatar boxerab commented on June 4, 2024

Alright, I think I understand :) , but yes, I find this unusual.
Thanks,
Aaron

from openjph.

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