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Ghostscript (gstoraster): Introduce cupsHalftoneType dithering algorithms #642

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Ghostscript (gstoraster): Introduce cupsHalftoneType dithering algorithms #642

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f2bbe18
Ghostscript (gstoraster): Introduce cupsHalftoneType dithering algori…
ValdikSS May 27, 2025
48de598
Ghostscript (gstoraster): add bi-level threshold support
ValdikSS May 27, 2025
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89 changes: 89 additions & 0 deletions filter/gstoraster.c
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Original file line number Diff line number Diff line change
Expand Up @@ -64,6 +64,14 @@ typedef enum {
OUTPUT_FORMAT_PXL
} OutFormatType;

typedef enum
{
HALFTONE_DEFAULT,
HALFTONE_STOCHASTIC,
HALFTONE_FOO2ZJS,
HALFTONE_BI_LEVEL
} cups_halftone_type_t;

#ifdef CUPS_RASTER_SYNCv1
typedef cups_page_header2_t gs_page_header;
#else
Expand Down Expand Up @@ -642,6 +650,8 @@ main (int argc, char **argv, char *envp[])
struct sigaction sa;
cm_calibration_t cm_calibrate;
int pxlcolor = 1;
cups_halftone_type_t halftonetype = HALFTONE_DEFAULT;
char *halftone_tmp = NULL;
#ifdef HAVE_CUPS_1_7
int pwgraster = 0;
ppd_attr_t *attr;
Expand Down Expand Up @@ -971,6 +981,35 @@ main (int argc, char **argv, char *envp[])
cupsArrayAdd(gs_args, strdup(tmpstr));
}

if ((t = cupsGetOption("cupsHalftoneType", num_options, options)) != NULL ||
(t = cupsGetOption("halftone-type", num_options, options)) != NULL)
halftone_tmp = t;
else if (ppd && (attr = ppdFindAttr(ppd, "DefaultcupsHalftoneType", NULL)) != NULL)
halftone_tmp = attr->value;

if (halftone_tmp) {
if (!strcasecmp(halftone_tmp, "true") || !strcasecmp(halftone_tmp, "on") ||
!strcasecmp(halftone_tmp, "yes") || !strcasecmp(halftone_tmp, "stochastic"))
halftonetype = HALFTONE_STOCHASTIC;
else if (!strcasecmp(halftone_tmp, "foo2zjs"))
halftonetype = HALFTONE_FOO2ZJS;
else if (!strcasecmp(halftone_tmp, "bi-level"))
halftonetype = HALFTONE_BI_LEVEL;
}

/* For bi-level type, also check print-color-mode, the way it is
handled by Poppler pwgtoraster/pdftoraster/pclmtoraster utilities. */
if ((t = cupsGetOption("print-color-mode", num_options, options)) != NULL &&
!strcasecmp(t, "bi-level"))
halftonetype = HALFTONE_BI_LEVEL;

/* Use Stochastic Halftone dithering found in GhostScript stocht.ps library file.
It is activated automatically. */
if (halftonetype == HALFTONE_STOCHASTIC) {
fprintf(stderr, "DEBUG: Ghostscript using Stochastic Halftone dithering.\n");
cupsArrayAdd(gs_args, strdup("stocht.ps"));
}

/* Switch to taking PostScript commands on the Ghostscript command line */
cupsArrayAdd(gs_args, strdup("-c"));

Expand Down Expand Up @@ -1016,6 +1055,56 @@ main (int argc, char **argv, char *envp[])
} else
fprintf(stderr, "DEBUG: Ghostscript using Any-Part-of-Pixel method to fill paths.\n");

/* Use halftone dithering algorithm found in foo2zjs-pstops file */
if (halftonetype == HALFTONE_FOO2ZJS) {
fprintf(stderr, "DEBUG: Ghostscript using foo2zjs Halftone dithering.\n");
cupsArrayAdd(gs_args, strdup("/SpotDot { 180 mul cos exch 180 mul cos add 2 div } def\
<<\
/HalftoneType 5\
/Cyan <<\
/HalftoneType 1\
/AccurateScreens true\
/Frequency 150\
/Angle 105\
/SpotFunction /SpotDot load\
>>\
/Magenta <<\
/HalftoneType 1\
/AccurateScreens true\
/Frequency 150\
/Angle 165\
/SpotFunction /SpotDot load\
>>\
/Yellow <<\
/HalftoneType 1\
/AccurateScreens true\
/Frequency 150\
/Angle 30\
/SpotFunction /SpotDot load\
>>\
/Black <<\
/HalftoneType 1\
/AccurateScreens true\
/Frequency 150\
/Angle 45\
/SpotFunction /SpotDot load\
>>\
/Default <<\
/HalftoneType 1\
/AccurateScreens true\
/Frequency 150\
/Angle 37\
/SpotFunction /SpotDot load\
>>\
>> /Default exch /Halftone defineresource sethalftone"));
}

/* Use simple threshold (bi-level) halftone algorithm */
if (halftonetype == HALFTONE_BI_LEVEL) {
fprintf(stderr, "DEBUG: Ghostscript using Bi-Level Halftone dithering.\n");
cupsArrayAdd(gs_args, strdup("{ .5 gt { 1 } { 0 } ifelse} settransfer"));
}

/* Mark the end of PostScript commands supplied on the Ghostscript command
line (with the "-c" option), so that we can supply the input file name */
cupsArrayAdd(gs_args, strdup("-f"));
Expand Down