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Ghostscript (gstoraster): Introduce cupsHalftoneType dithering algorithms #92

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Merged
tillkamppeter merged 2 commits into from
Sep 29, 2025
+98 −0
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Ghostscript (gstoraster): Introduce cupsHalftoneType dithering algorithms #92

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7a979f5
Ghostscript (gstoraster): Introduce cupsHalftoneType dithering algori…
ValdikSS May 26, 2025
71742d2
Ghostscript (gstoraster): add bi-level threshold support
ValdikSS May 27, 2025
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98 changes: 98 additions & 0 deletions cupsfilters/ghostscript.c
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Original file line number Diff line number Diff line change
Expand Up @@ -44,6 +44,14 @@ typedef enum gs_doc_e

typedef cups_page_header_t gs_page_header;

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

static gs_doc_t
parse_doc_type(FILE *fp)
{
Expand Down Expand Up @@ -805,6 +813,7 @@ cfFilterGhostscript(int inputfd, // I - File descriptor input
struct sigaction sa;
cf_cm_calibration_t cm_calibrate;
int pxlcolor = 0; // 1 if printer is color printer otherwise 0.
cups_halftone_type_t halftonetype = HALFTONE_DEFAULT;
ipp_attribute_t *ipp_attr;
cf_logfunc_t log = data->logfunc;
void *ld = data->logdata;
Expand Down Expand Up @@ -1606,6 +1615,37 @@ cfFilterGhostscript(int inputfd, // I - File descriptor input
else if (!cm_disabled)
cupsArrayAdd(gs_args, strdup("-sOutputICCProfile=srgb.icc"));

if ((t = cupsGetOption("cupsHalftoneType", num_options, options)) != NULL ||
(t = cupsGetOption("halftone-type", num_options, options)) != NULL)
{
if (!strcasecmp(t, "true") || !strcasecmp(t, "on") ||
!strcasecmp(t, "yes") || !strcasecmp(t, "stochastic"))
halftonetype = HALFTONE_STOCHASTIC;
else if (!strcasecmp(t, "foo2zjs"))
halftonetype = HALFTONE_FOO2ZJS;
else if (!strcasecmp(t, "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)
{
if (log) log(ld, CF_LOGLEVEL_DEBUG,
"cfFilterGhostscript: Ghostscript using Stochastic Halftone dithering.");
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 @@ -1662,6 +1702,64 @@ cfFilterGhostscript(int inputfd, // I - File descriptor input
"cfFilterGhostscript: Ghostscript using Any-Part-of-Pixel method to "
"fill paths.");

//
// Use halftone dithering algorithm found in foo2zjs-pstops file
//
if (halftonetype == HALFTONE_FOO2ZJS)
{
if (log) log(ld, CF_LOGLEVEL_DEBUG,
"cfFilterGhostscript: Ghostscript using foo2zjs Halftone dithering.");
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)
{
if (log) log(ld, CF_LOGLEVEL_DEBUG,
"cfFilterGhostscript: Ghostscript using Bi-Level Halftone dithering.");
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