I'm looking into this now.

— linden.orig/indra/llimagej2coj/llimagej2coj.cpp 2007-06-26 18:46:57.00000>
+++ linden.patched/indra/llimagej2coj/llimagej2coj.cpp 2007-07-03 14:55:02.00>
@@ -211,10 +211,14 @@

/* set encoding parameters to default values */
opj_set_default_encoder_parameters(&parameters);

• parameters.tcp_rates[0] = 0;
• parameters.tcp_numlayers++;
• parameters.cp_disto_alloc = 1;
  parameters.cod_format = 0;
  + parameters.irreversible = 1;
  + parameters.tcp_distoratio[0] = 45.0f;
  + parameters.tcp_numlayers = 1;
  + parameters.cp_fixed_quality = 1;
  + if(raw_image.getComponents() >= 3){ + parameters.tcp_mct = 1; + }
  if (!comment_text)
  {
  parameters.cp_comment = "";

Notes/Recommendations:

This enables the "irreversible" aka lossy DWT, which is what KDU uses. The irreversible DWT is also the code path that Dzonatas and me have optimized quite a bit.

I use a single layer with rate distortion control, I haven't looked at what KDU does. This part could use tuning.

I enable the MCT when there's at least three channels, basically this transforms RGB to YUV format before encoding. This should always be used with RGB images, KDU does, OpenJPEG's command line encoder does, however OpenJPEG's codec configuration API is rather icky (non-existent) and doesn't do this for you. Best bet seems to be to look at codec/image_to_j2k.c for how to set codec parameters.

Ultimately we do want a way to upload lossless textures for use with sculpt maps. MCT may not be of help there.

Note that tcp_rates is a float, so the constants should be in float format to prevent un-necessary casts.

We need to work out some kind of UI to allow users to upload lossless textures, preferably only when uploading sculpt maps. I don't enable MCT when doing lossless at the moment, really more testing needs to be done to see if MCT does any good with sculpt maps. Not using MCT seems to be what caused the strange colors and color fringing with avatar textures.

1.3 should have some major speed improvements if things go to plan.

Can we get this merged please?

1.18.3.x seems to be distributing with OpenJPEG 1.2 now anyway so this patch should work.