histogram
Tcl_Obj* imageObj

/*
 * This operation is a general histogram generator
 */

crimp_image*     image;
int              x, y, c, i, count, maxv, largegrey;
int*             histogram;
Tcl_Obj*         d; /* dict of histograms, indexed by channel name */
Tcl_Obj*         h; /* histogram dict, indexed by pixel value */
Tcl_Obj*         k; /* channel name as Tcl_Obj, for the main dict */

crimp_input_any (imageObj, image);
ASSERT_NOTIMGTYPE(image,grey32);
/*
 * Actually NOT any. The code below is not able to handle grey32, as images
 * with these types can have 4G possible values, for which we cannot allocate
 * a full counter array.
 *
 * XXX This needs fixing. Use of a hashtable to allocate only pixel values
 * actually seen. Will still run into trouble for extreme images which do
 * contain all the possible values.
 */

largegrey = image->itype == crimp_imagetype_find ("crimp::image::grey16");
if (largegrey) {
    maxv = 65536;
} else {
    maxv = 256;
}

histogram = NALLOC (maxv * image->itype->channels, int);
memset (histogram, '\0', maxv * image->itype->channels * sizeof (int));

/*
 * Count the pixel values.
 */

#define BUCKET(c,v) histogram [((c) * maxv + (v))]

if (largegrey) {
    for (y = 0; y < image->h; y++) {
	for (x = 0; x < image->w; x++) {
	    BUCKET (0, GREY16 (image, x, y)) ++;
	}
    }
} else {
    for (y = 0; y < image->h; y++) {
	for (x = 0; x < image->w; x++) {
	    for (c = 0; c < image->itype->channels; c++) {
		BUCKET (c, CH (image, c, x, y)) ++;
	    }
	}
    }
}

/*
 * Convert the data into a dictionary to return.
 *
 * XXX: For the very large histograms of grey32 (4GB possible values) it would
 * be sensible to suppress the entries for all pixel values which are not
 * used, i.e. have a count of zero.
 */

d = Tcl_NewDictObj ();

for (c = 0; c < image->itype->channels; c++) {

    k = Tcl_NewStringObj (image->itype->cname [c],-1);
    h = Tcl_NewDictObj ();

    for (i = 0; i < maxv; i++) {
	count = BUCKET (c, i);

	/*
	 * XXX future optimization: keep a hash table of the Int objects, and
	 * share them as much a is possible.
	 */

	Tcl_DictObjPut (interp, h,
			Tcl_NewIntObj (i),
			Tcl_NewIntObj (count));
    }

    Tcl_DictObjPut (interp, d, k, h);
}

ckfree ((char*) histogram);

Tcl_SetObjResult(interp, d);
return TCL_OK;


/* vim: set sts=4 sw=4 tw=80 et ft=c: */
/*
 * Local Variables:
 * mode: c
 * c-basic-offset: 4
 * fill-column: 78
 * End:
 */