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* Threshold screen pixel processing object.
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* (Simplified from DPS code)
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* Author: Graeme W. Gill
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* Copyright 2005, 2012 Graeme W. Gill
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* All rights reserved.
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* This material is licenced under the GNU AFFERO GENERAL PUBLIC LICENSE Version 3 :-
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* see the License.txt file for licencing details.
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//#include "xcolorants.h"
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/* ----------------------------------------------------------- */
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# define DBG(text) printf text ; fflush(stdout);
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/* ----------------------------------------------------------- */
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/* Setup a set of screens */
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/* Screen data is used that best matches the requested parameters. */
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#include "screens.h" /* Pre-generated screen patterns */
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/* Screen a single color plane */
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void screen_thscreens( /* Pointer to dither function */
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thscreens *t, /* Screening object pointer */
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int width, int height, /* Width and height to screen in pixels */
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int xoff, int yoff, /* Offset into screening pattern */
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unsigned char *in, /* Input pixel buffer */
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unsigned long ipitch, /* Increment between input lines */
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unsigned char *out, /* Output pixel buffer */
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unsigned long opitch /* Increment between output lines */
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for (i = 0; i < t->np; i++)
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t->sc[i]->screen(t->sc[i], width, height, xoff, yoff, in + 2 * i, t->np, ipitch,
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out + i, t->np, opitch);
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/* Delete a thscreens */
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void del_thscreens(thscreens *t) {
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for (i = 0; i < t->np; i++)
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t->sc[i]->del(t->sc[i]);
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/* Create a new thscreens object matching the parameters */
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thscreens *new_thscreens(
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int exact, /* Return only exact matches */
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int nplanes, /* Number of planes to screen */
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double asp, /* Target aspect ratio (== dpiX/dpiY) */
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int size, /* Target size */
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sc_iencoding ie, /* Input encoding - must be scie_16 */
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int oebpc, /* Output encoding bits per component - must be 8 */
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int oelev, /* Output encoding levels. Must be <= 2 ^ oebpc */
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int *oevalues, /* Optional output encoding values for each level */
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/* Must be oelev entries. Default is 0 .. oelev-1 */
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sc_oorder oo, /* Output bit ordering */
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double overlap, /* Overlap between levels, 0 - 1.0 */
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void **cntx, /* List of contexts for lookup table callback */
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double (**lutfunc)(void *cntx, double in) /* List of callback function, NULL if none */
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double bamatch; /* Best aspect match */
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int bsize = 100000; /* Best size match */
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int swap = 0; /* width and height will need swapping */
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DBG(("thscreens: new called with:\n"));
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DBG((" nplanes = 0x%x\n",nplanes));
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DBG((" asp = %f\n",asp));
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DBG((" ie = %d\n",ie));
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DBG((" oebpc = %d\n",oebpc));
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DBG((" oelev = %d\n",oelev));
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DBG((" oo = %d\n",oo));
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DBG((" overlap = %f\n",overlap));
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if (asp < 1.0) { /* All screens[] have asp >= 1.0 */
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DBG(("thscreens: aspect swap needed\n"));
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if ((t = (thscreens *)calloc(1, sizeof(thscreens))) == NULL) {
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DBG(("thscreens: malloc of thscreens failed\n"));
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t->np = nplanes; /* Number of planes */
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DBG(("thscreens no planes = %d\n",t->np));
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t->screen = screen_thscreens;
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t->del = del_thscreens;
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if ((t->sc = malloc(sizeof(thscreen *) * t->np)) == NULL) {
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DBG(("thscreens: malloc of thscreens->sc[] failed\n"));
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DBG(("thscreens: searching amongst %d screens, exact = %d\n",NO_SCREENS,exact));
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DBG(("thscreens: looking for non-exact match\n"));
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/* Synthesise a set of screens from what's there */
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/* (Don't bother with matching the colorspace) */
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for (i = 0;i < NO_SCREENS; i++) {
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double thamatch; /* This aspect match */
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int thsize; /* This size match */
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thamatch = asp/screens[i].asp;
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thamatch = 1.0/thamatch;
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if (bi < 0 || (thamatch < bamatch)) { /* No best or new best */
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DBG(("thscreens: new best with aspmatch %f\n",bamatch));
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continue; /* On to next */
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if (thamatch > bamatch) /* Worse aspect match */
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/* Same on aspect ratio. Check size */
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thsize = size - screens[i].size;
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if (thsize < bsize) { /* New better size match */
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DBG(("thscreens: new best with size %d\n",bsize));
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if (bi < 0) /* Strange */
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/* Create each screening object from one defined screen. */
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/* Use the 0'th plane screen */
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/* Stagger the screens with a round of 9 offset */
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for (i = 0; i < t->np; i++) {
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int xoff = ((i % 3) * screens[bi].width)/3;
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int yoff = (((i/3) % 3) * screens[bi].height)/3;
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double (*lf)(void *cntx, double in) = 0;
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DBG(("thscreens: creating plane %d/%d thscreen, offset %d %d\n",i,t->np,xoff,yoff));
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if ((t->sc[i] = new_thscreen(screens[bi].width, screens[bi].height, xoff, yoff,
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screens[bi].asp, swap, screens[bi].list[0],
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ie, oebpc, oelev, oevalues, oo, overlap,
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for (--i; i >= 0; i--)
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t->sc[i]->del(t->sc[i]);
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DBG(("thscreens: new_thscreen() failed\n"));
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DBG(("thscreens: returning nonexact match\n"));
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/* ----------------------------------------------------------- */
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/* The kernel screening routin */
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struct _thscreen *t, /* Screening object pointer */
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int width, int height, /* Width and height to screen in pixels */
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int xoff, int yoff, /* Offset into screening pattern (must be +ve) */
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unsigned char *_in, /* Input pixel buffer */
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unsigned long ipinc, /* Increment between input pixels */
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unsigned long ipitch, /* Increment between input lines */
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unsigned char *out, /* Output pixel buffer */
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unsigned long opinc, /* Increment between output pixels */
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unsigned long opitch /* Increment between output lines */
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unsigned short *in = (unsigned short *)_in; /* Pointer to input pixel sized values */
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int *lut = t->lut; /* Copy of 8 or 16 -> 16 bit lookup table */
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unsigned char **oth, **eth; /* Current lines start, origin and end in screening table. */
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int thtsize; /* Overall size of threshold table */
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unsigned char **eeth; /* Very end of threshold table */
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unsigned short *ein = in + height * ipitch; /* Vertical end pixel marker */
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unsigned short *ein1; /* Horizontal end pixel markers */
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unsigned char **sth; /* Start point of line intable */
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sth = t->thp + (yoff % t->sheight) * t->twidth;
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oth = sth + (xoff % t->swidth); /* Orgin of pattern to start from */
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eth = sth + t->swidth; /* Ending point to wrap back */
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thtsize = t->twidth * t->theight;
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eeth = t->thp + thtsize; /* very end of table */
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ein1 = in + ipinc * width;
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for (; in < ein; in += ipitch, ein1 += ipitch, out += opitch) {
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unsigned char **th = oth; /* Threshold table origin */
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unsigned short *ip = in; /* Horizontal input pointer */
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unsigned char *op = out; /* Horizontal output pointer */
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/* Do pixels one output byte at a time */
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for (; ip < ein1; ip += ipinc, op += opinc) {
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*op = (unsigned char)th[0][tt];
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/* Advance screen table pointers with vertical wrap */
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/* ----------------------------------------------------------- */
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/* We're done with the screening object */
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/* Create a new thscreen object */
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/* Return NULL on error */
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thscreen *new_thscreen(
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int width, /* width in pixels of screen */
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int height, /* Height in pixels of screen */
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int xoff, int yoff, /* Pattern offsets into width & height */
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double asp, /* Aspect ratio of screen (== dpiX/dpiY) */
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int swap, /* Swap X & Y to invert aspect ratio & swap width/height */
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ccoord *thli, /* Pointer to list of threshold coordinates */
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sc_iencoding ie, /* Input encoding - must be scie_16 */
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int oebpc, /* Output encoding bits per component - must be 8 */
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int oelev, /* Output encoding levels. Must be <= 2 ^ oebpc */
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int *oevalues, /* Optional output encoding values for each level */
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/* Must be oelev entries. Default is 0 .. oelev-1 */
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sc_oorder oo, /* Output bit ordering */
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double olap, /* Overlap between levels, 0 - 1.0 */
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void *cntx, /* Context for LUT table callback */
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double (*lutfunc)(void *cntx, double in) /* Callback function, NULL if none */
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thscreen *t; /* Object being created */
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int npix; /* Total pixels in screen */
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double mrang; /* threshold modulation range */
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double **fthr; /* Floating point threshold array */
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DBG(("new_thscreen() called, oebpc = %d\n",oebpc));
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DBG(("new_thscreen() called, oelev = %d\n",oelev));
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/* Sanity check overlap */
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/* Sanity check parameters */
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DBG(("new_thscreen() ie %d != scie_16\n",ie));
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DBG(("new_thscreen() oebpc %d != 8\n",oebpc));
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if (oelev < 2 || oelev > (1 << oebpc)) {
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DBG(("new_thscreen() oelev %d > 2^%d = %d\n",oelev,1 << oebpc,oebpc));
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if ((t = (thscreen *)calloc(1, sizeof(thscreen))) == NULL) {
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DBG(("new_thscreen() calloc failed\n"));
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/* Instantiation parameters */
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if (oevalues != NULL) {
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for (i = 0; i < t->oelev; i++) {
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if (oevalues[i] >= (1 << t->oebpc)) {
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DBG(("new_thscreen() oevalues[%d] value %d can't fit in %d bits\n",i,oevalues[i],t->oebpc));
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t->oevalues[i] = oevalues[i];
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for (i = 0; i < t->oelev; i++)
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/* Create a suitable LUT from the given function */
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/* Input is either 8 or 16 bits, output is always 16 bits */
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DBG(("new_thscreen() about to create LUT\n"));
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if ((t->lut = (int *)malloc(sizeof(int) * 65536)) == NULL) {
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DBG(("new_thscreen() malloc of 16 bit LUT failed\n"));
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for (i = 0; i < 65536; i++) {
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if (lutfunc != NULL) {
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double v = i/65535.0;
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v = lutfunc(cntx, v);
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t->lut[i] = (int)(v * 65535.0 + 0.5);
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/* Screen definition parameters */
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DBG(("new_thscreen() target width %d, height %d, asp %f\n",t->swidth,t->sheight,t->asp));
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DBG(("new_thscreen() given width %d, height %d, asp %f\n",width,height,asp));
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npix = t->swidth * t->sheight; /* Total pixels */
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/* Allow for read of a words worth of pixels from within screen: */
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DBG(("new_thscreen() tot pix %d, lev %d, bpp %d\n",npix,t->oelev,t->oebpc));
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t->twidth = t->swidth + (8/t->oebpc) -1;
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t->theight = t->sheight;
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DBG(("new_thscreen() th table size = %d x %d\n",t->twidth,t->theight));
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DBG(("new_thscreen() about to turn screen list into float threshold matrix\n"));
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/* Convert the list of screen cells into a floating point threshold array */
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fthr = dmatrix(0, t->sheight-1, 0, t->swidth-1); /* Temporary matrix */
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double tt = xoff; /* Swap offsets to align with orientation */
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for (i = 0; i < npix; i++)
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fthr[thli[i].x][thli[i].y] = (double)(i/(npix - 1.0));
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for (i = 0; i < npix; i++)
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fthr[thli[i].y][thli[i].x] = (double)(i/(npix - 1.0));
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/* The range that the screen has to modulate */
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/* over to cross all the thresholds evenly. */
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mrang = 65535.0/(t->oelev - 1.0);
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DBG(("new_thscreen() raw modulation rande = %f\n",mrang));
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/* Modify the modulation range to accomodate any level overlap */
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if (olap > 0.0 && t->oelev > 2) {
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mrang = ((t->oelev - 2.0) * olap * mrang + 65535.0)/(t->oelev - 1.0);
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DBG(("new_thscreen() modulation adjusted for overlap = %f\n",mrang));
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/* Init the threshold table. It holds the quantized, encoded output */
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/* values, allowing an input value offset by the screen to be */
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/* thresholded directly into the output value. We allow a guard band at */
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/* each end for the effects of the screen modulating the input value. */
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DBG(("new_thscreen() about to init threshold table\n"));
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t->tht = &t->_tht[32768]; /* base allows for -ve & +ve range */
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for (i = -32768; i < (2 * 65536) + 32768; i++) {
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if (i < mrang) { /* Lower guard band */
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t->tht[i] = t->oevalues[0];
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} else if (i >= 65535) { /* Upper guard band */
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t->tht[i] = t->oevalues[t->oelev-1];
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} else { /* Middle range */
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t->tht[i] = t->oevalues[1 + (int)((t->oelev - 2.0) * (i - mrang)/(65535.0 - mrang))];
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/* Allocate the 2D table of pointers into the */
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/* threshold table that encodes the screen offset. */
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if ((t->thp = (unsigned char **)malloc(sizeof(unsigned char *)
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* t->twidth * t->theight)) == NULL) {
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free_dmatrix(fthr, 0, t->sheight-1, 0, t->swidth-1);
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DBG(("new_thscreen() malloc of threshold pointer matrix failed\n"));
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/* Setup the threshold pointer array to point into the apropriate */
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/* point into the threshold array itself. This implicitly adds */
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/* the screen pattern offset value to the input before thresholding it. */
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/* The input screen offsets are applied at this point too. */
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DBG(("new_thscreen() about to init threshold pointer table\n"));
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for (i = 0; i < t->twidth; i++) {
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for (j = 0; j < t->theight; j++) {
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double sov = fthr[(j+yoff) % t->sheight][(i+xoff) % t->swidth];
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int tho = (int)((mrang - 1.0) * (1.0 - sov) + 0.5);
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t->thp[j * t->twidth + i] = &t->tht[tho];
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free_dmatrix(fthr, 0, t->sheight-1, 0, t->swidth-1);
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DBG(("new_thscreen() about to setup method pointers\n"));
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t->screen = thscreen16_8;
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DBG(("new_thscreen() done\n"));
added
removed
render/thscreen.c
