FAX T.6 decompression fixed for images with black in the last pixel of lines.

Colour and grey images can down be dithered down to bi-level images for transmission as faxes. More movement towards T.42 support
2025-08-14 01:49:05 +00:00 · 2012-08-04 03:45:09 +08:00
parent e35221b981
commit e523076274
29 changed files with 916 additions and 446 deletions
--- a/libs/spandsp/src/make_cielab_luts.c
+++ b/libs/spandsp/src/make_cielab_luts.c
@@ -0,0 +1,92 @@
+/*
+ * SpanDSP - a series of DSP components for telephony
+ *
+ * make_cielab_luts.c - Create the look up tables for CIELab colour management
+ *
+ * Written by Steve Underwood <steveu@coppice.org>
+ *
+ * Copyright (C) 2011 Steve Underwood
+ *
+ * All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+/*! \file */
+
+#if defined(HAVE_CONFIG_H)
+#include "config.h"
+#endif
+
+#include <inttypes.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <memory.h>
+#if defined(HAVE_TGMATH_H)
+#include <tgmath.h>
+#endif
+#if defined(HAVE_MATH_H)
+#include <math.h>
+#endif
+
+typedef struct
+{
+    float L;
+    float a;
+    float b;
+} cielab_t;
+
+int main(int argc, char *argv[])
+{
+    float r;
+    uint8_t srgb;
+    int i;
+
+    printf("static const float srgb_to_linear[256] =\n");
+    printf("{\n");
+    for (i = 0;  i < 256;  i++)
+    {
+        /* Start with "i" as the sRGB value */
+        r = i/256.0f;
+
+        /* sRGB to Linear RGB */
+        r = (r > 0.04045f)  ?  powf((r + 0.055f)/1.055f, 2.4f)  :  r/12.92f;
+        
+        printf((i < 255)  ?  "    %f,\n"  :  "    %f\n", r);
+    }
+    printf("};\n");
+    
+    printf("static const uint8_t linear_to_srgb[4096] =\n");
+    printf("{\n");
+    for (i = 0;  i < 4096;  i++)
+    {
+        /* Start with "i" as the linear RGB value */
+        /* Linear RGB to sRGB */
+        r = i/4096.0f;
+
+        r = (r > 0.0031308f)  ?  (1.055f*powf(r, 1.0f/2.4f) - 0.055f)  :  r*12.92f;
+
+        r = floorf(r*256.0f);
+
+        srgb = (r < 0)  ?  0  :  (r <= 255)  ?  r  :  255;
+
+        printf((i < 4095)  ?  "    %d,\n"  :  "    %d\n", srgb);
+    }
+    printf("};\n");
+    return 0;
+}
+/*- End of function --------------------------------------------------------*/
+/*- End of file ------------------------------------------------------------*/