Леон прислал мне ещё одно письмо с ответами:
Вопрос: IW44 - это lossy формат или нет?
IW44 with the max number of slices *is* lossless for gray level images.
For rgb images the color transform loses one bit (so you practically have 128 levels instead of 256).
You have to use the -crcbfull option to minimize the rgb loss.
Вопрос: Один человек критиковал IW44 и сказал, что IW44 слишком размывчатый (blurry) для него (по сравнению с JPEG2000).
At the highest quality, IW44 is lossless in luminance.
Therefore the "blurriness" must come from the chrominance tricks.
Try -slices=199 -crcbfull.
Вопрос: Этот человек сказал, что информация в
http://leon.bottou.org/slides/djvu/index.djvu?djvuopts&page=24 наверняка устарела и JPEG2000 значительно улучшился с тех времён. Когда этот документ был написан - вероятно, в 1998 году?
Probably around 2000. Note that improvements are necessarily limited because jpeg2k must comply with the standard, and the standard has not changed.
Wevelets are not like djvu. There are not many ways to compress a jpeg2k file. The only possible improvements are pre- and post-filters (which play with the perceived image quality at the expense of true snr) as well as adaptive quantization in various sections of the image.
Btw. Does you friend make this assessment by comparing original and compressed images (which one is closest to the original) or by comparing two compressed image (which one looks better without reference to the original) ?
The latter comparison is technically incorrect. But it is true that you can tweak compression to do that.
Вопрос: К тому же, сейчас появились новые реализации JPEG2000 - которых не было в 1998 году. Например, кодек LuraTech JPEG2000, скорее всего, гораздо эффективнее базовой JasPer (т.е. стандартной JPEG2000-реализации).
Implementations can go faster. Accuracy improvements are limited to the above tricks.
Вопрос: Становится ли формат DjVu устаревшим?
It is certainly aging because nobody works in depth on it.
Вопрос: Бурное развитие всевозможных JPEG2000-реализаций - представляет ли оно угрозу существованию формата DjVu?
The biggest killer was certainly the brain-damaged business strategies of AT&T and then Lizardtech.
Celartem and Caminova are more resonable but lack resources.
Note that IW44 was never designed to compete with Jpeg2000.
It was just designed to support the DjVu document encoding.
The Jpeg2000 proposals at the time were very different from IW44 and unsuitable for DjVu.
The final Jpeg2000 is much closer to IW44 (very close in fact!)
This is why I find perfectly fine to use Jpeg2000 inside DjVu if it fits the bill.
Вопрос: Мне бы не хотелось, чтобы формат DjVu канул в забвение. Наверняка формату DjVu необходим некоторый "апдейт" - чтобы не отставать от развития JPEG2000.
The reality is the following:
If Caminova does not do it, nobody will.
In their great wisdom^H^H^H^H^H^H greed, the AT&T lawyer made sure that none of the initial DjVu authors would ever receive a dime from DjVu products.
Although I consider that they are the most alive part of DjVu, DjVuLibre and DjVu.org are built on pure goodwill and bring zero dollars.
Yann and I have paid ten years of bandwidth expense on our salaries.
As a result none of us has the economical opportunity to spend serious time on improving DjVu.
- L.