Introduction to OpenJPEG?

[Florian Hofmann]

Hi everyone,

i am currently working on a temporary data storage for a volume
renderer. I am thinking on moving from standard tiff to openjpeg due
to it's build in detail levels.

Now, while looking for some introductionary material i cannot find
anything. The only documentation seems to be the doxygen generated
code apidoc.

Is there a 'tutorial' on how to use the open jpeg library?

Kind Regards,
Florian

[szuk...@arcor.de]

On Mon, 27 Sep 2010 01:53:53 -0700 (PDT), fha...@googlemail.com,
wrote:

>Is there a 'tutorial' on how to use the open jpeg library?

A general 'tutorial' can be found here:
http://www.openjpeg.org/
Follow the link on the left side: 'Documentation'

Another 'tutorial' can be found in the source code: e.g. of
the binaries in the 'codec/' and/or 'mj2/' directory.

winfried

[Florian Hofmann]

Thanks for the pointers :)

Of course i was looking in the documentation section ... but i didn't search the source.

Nevertheless ... there should be a 'simple file io' tutorial on the openjpeg site. A simple example on how to create and write a jp2 file or open and read it. Guys who are using the library will have done this and it shouldn't be too hard, or is it?

Kind regards,

Florian

2010/9/27 <szuk...@arcor.de>

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[szuk...@arcor.de]

On Mon, 27 Sep 2010 21:44:52 +0200, florian...@fh-bielefeld.de,
wrote:

>Nevertheless ... there should be a 'simple file io' tutorial
>on the openjpeg site. A simple example on
>how to create and write a jp2 file or open and read it.
>Guys who are using the library will have done
>this and it shouldn't be too hard, or is it?

It is hard.

-------------- HOWTO READ A STILL IMAGE -----------------
A J2K file has an 'image/j2k' mime type, a JP2 file has an
'image/jp2' mime type.

'codec/j2k_to_image.c' shows how to read a file containing
a still image.

The format may be:

FORMAT=(CODEC_J2K | CODEC_JP2 ).

opj_dparameters_t parameters;
opj_image_t *image;
opj_dinfo_t *dinfo;
unsigned char *buf;
long buf_len;
FILE *reader;

/* Your J2K data shall be in "example.j2k", so FORMAT=CODEC_J2K :
*/
reader = fopen("PATH/TO/example.j2k", "rb");
fseek(reader, 0, SEEK_END);
buf_len = ftell(reader);
fseek(reader, 0, SEEK_SET);
buf = (unsigned char*) malloc(buf_len);
fread(buf, 1, buf_len, reader);
fclose(reader);

opj_set_default_decoder_parameters(&parameters);

dinfo = opj_create_decompress(FORMAT);

opj_setup_decoder(dinfo, &parameters);

cio = opj_cio_open((opj_common_ptr)dinfo, buf, buf_len);

image = opj_decode(dinfo, cio);

'opj_decode()' fills image->comps[0-3].data, if the file is a valid
J2K/JP2 file. If it is not, then 'image' should be NULL.

What is in a file/image depends on the

typedef enum COLOR_SPACE {
CLRSPC_UNKNOWN = -1, /**< not supported by the library */
CLRSPC_UNSPECIFIED = 0, /**< not specified in the codestream */
CLRSPC_SRGB = 1, /**< sRGB */
CLRSPC_GRAY = 2, /**< grayscale */
CLRSPC_SYCC = 3 /**< YUV */
} OPJ_COLOR_SPACE;

returned in the 'image->color_space' ( see openjpeg.h ).

An image may have up to four channels:

image->numcomps == 1 : GRAY image
image->numcomps == 2 : GRAY_ALPHA image
image->numcomps == 3 : sRGB image or sYCC image
image->numcomps == 4 : sRGB_ALPHA image

-------------- HOWTO READ A MOVIE -----------------
The 'mj2' file has the 'movie/mj2' mime type. Reading an MJ2
file is more complicated: the movie consists of tracks. A
track consists of samples. The following can be found in
mj2/extract_j2k_from_mj2.c : the binary reads the samples
of a track and creates one J2K file for each sample.

FILE *reader, *writer;
opj_dinfo_t* dinfo;
opj_mj2_t *movie;
mj2_tk_t *track;
mj2_sample_t *sample;
unsigned char *buf;
mj2_dparameters_t parameters;
int tnum;
unsigned int snum;
char outbase[50], outfilename[50];

strcpy(outbase, "dstdir/dst_basename");

reader = fopen("PATH/TO/infilename.mj2", "rb");
dinfo = mj2_create_decompress();
movie = (opj_mj2_t*) dinfo->mj2_handle;
mj2_setup_decoder(movie, &parameters);
mj2_read_struct(reader, movie);

tnum = 0;
while (movie->tk[tnum].track_type != 0)
tnum ++;

track = &movie->tk[tnum];

for (snum=0; snum < track->num_samples; snum++)
{
sample = &track->sample[snum];
buf = (unsigned char*) malloc (sample->sample_size-8);

fseek(file,sample->offset+8,SEEK_SET);

sprintf(outfilename,"%s_%05d.j2k",outbase, snum);
fread(buf,sample->sample_size-8,1, reader);

writer = fopen(outfilename, "wb");

fwrite(buf,sample->sample_size-8,1,outfile);
fclose(writer);
free(buf);
}
fclose(reader);

if(dinfo)
{
mj2_destroy_decompress(movie);
}

HOWTO WRITE is too complicated for a mail. Yes, there should be
a tutorial.

winfried

[szuk...@arcor.de]

And the tutorial should be bug free:

fseek(reader,sample->offset+8,SEEK_SET);

fwrite(buf,sample->sample_size-8,1,writer);

winfried

[Florian Hofmann]

Hmm... by the look of it it is hard. I'll have to take a look at the sources at work.

Another two questions: does the library support multiple images per file and tile based io? (Or another way to get a subrange of the image?)

Kind regards,
Florian

winfried

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[Abdul-Bari Khan]

I am finding that opj_cio_open is not there in the library openjp2 ver 2.1.