New filter colorenhance: increase color contrast of video

src/filter/CMakeLists.txt

@@ -31,6 +31,7 @@ add_subdirectory (cluster)
 add_subdirectory (colgate)
 add_subdirectory (coloradj)
 add_subdirectory (colordistance)
+add_subdirectory (colorenhance)
 add_subdirectory (colorize)
 add_subdirectory (colorhalftone)
 add_subdirectory (colortap)

src/filter/colorenhance/CMakeLists.txt

@@ -0,0 +1,11 @@
+set (SOURCES colorenhance.c)
+set (TARGET colorenhance)
+
+if (MSVC)
+  set (SOURCES ${SOURCES} ${FREI0R_DEF})
+endif (MSVC)
+
+add_library (${TARGET} MODULE ${SOURCES})
+set_target_properties (${TARGET} PROPERTIES PREFIX "")
+
+install (TARGETS ${TARGET} LIBRARY DESTINATION ${LIBDIR})

src/filter/colorenhance/colorenhance.c

@@ -0,0 +1,202 @@
+/*
+ * colorenhance.c -- enhance the color contrast for vivid pictures
+ *
+ * Copyright (C) 2026 Cynthia (cynthia2048@proton.me)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * 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.
+ */
+
+#include <stdlib.h>
+
+#include <frei0r.h>
+#include <frei0r/math.h>
+
+#include "oklab.h"
+
+typedef struct
+{
+    unsigned int width, height;
+    uint8_t a_lut[256], 
+            b_lut[256];
+    float a_base, a_slope, 
+          b_base, b_slope;
+} colorenhance_t;
+
+static void make_sigmoid_lut(uint8_t *lut, float base, float steep)
+{
+  float k = expf(steep * 5.0) / 255.0;
+  float b = (base - 0.5) * 63.0;
+
+  for (int i = 0; i < 256; ++i)
+    lut[i] = CLAMP (255.0 / (1.0 + expf(-k * (i - b - 127.0))), 0, 255.0);
+}
+
+int f0r_init(void) 
+{
+    return 0;
+}
+
+void f0r_deinit(void) {}
+
+void f0r_get_plugin_info(f0r_plugin_info_t* sigmoidalInfo)
+{
+  sigmoidalInfo->name = "colorenhance";
+  sigmoidalInfo->author = "Cynthia";
+  sigmoidalInfo->plugin_type = F0R_PLUGIN_TYPE_FILTER;
+  sigmoidalInfo->color_model = F0R_COLOR_MODEL_RGBA8888;
+  sigmoidalInfo->frei0r_version = FREI0R_MAJOR_VERSION;
+  sigmoidalInfo->major_version = 1;
+  sigmoidalInfo->minor_version = 0;
+  sigmoidalInfo->num_params = 4;
+  sigmoidalInfo->explanation = "Enhances the color contrast in OkLab with sigmoidal transfers";
+}
+
+f0r_instance_t f0r_construct(unsigned int width, unsigned int height)
+{
+    colorenhance_t *inst = malloc(sizeof(colorenhance_t));
+
+    if (inst == NULL)
+        return NULL;
+
+    inst->width   = width;
+    inst->height  = height;
+    inst->a_base  = 0.55;
+    inst->a_slope = 0.4;
+    inst->b_base  = 0.5;
+    inst->b_slope = 0.4;
+
+    make_sigmoid_lut(inst->a_lut, inst->a_base, inst->a_slope);
+    make_sigmoid_lut(inst->b_lut, inst->b_base, inst->b_slope);
+    return inst;
+}
+
+void f0r_destruct(f0r_instance_t instance)
+{
+  free(instance);
+}
+
+void f0r_get_param_info(f0r_param_info_t* info, int index)
+{
+	switch (index) {
+		case 0:
+            info->name = "a_base";
+            info->type = F0R_PARAM_DOUBLE;
+            info->explanation = "Midpoint of sigmoidal curve for A channel";
+		break;
+        case 1:
+            info->name = "b_base";
+            info->type = F0R_PARAM_DOUBLE;
+            info->explanation = "Midpoint of sigmoidal curve for B channel";
+        break;
+        case 2:
+            info->name = "a_slope";
+            info->type = F0R_PARAM_DOUBLE;
+            info->explanation = "Steepness of the sigmoidal curve for A channel";
+        break;
+        case 3:
+            info->name = "b_slope";
+            info->type = F0R_PARAM_DOUBLE;
+            info->explanation = "Steepness of the sigmoidal curve for B channel";
+        break;
+	}
+}
+
+void f0r_set_param_value(f0r_instance_t instance, f0r_param_t param, int index)
+{
+	colorenhance_t* inst = (colorenhance_t*)instance;
+	switch (index)
+    {
+        case 0:
+            inst->a_base = *((double*)param);
+            make_sigmoid_lut(inst->a_lut, inst->a_base, inst->a_slope);
+        break;
+        case 1:
+            inst->b_base = *((double*)param);
+            make_sigmoid_lut(inst->b_lut, inst->b_base, inst->b_slope);
+        break;
+        case 2:
+            inst->a_slope = *((double*)param);
+            make_sigmoid_lut(inst->a_lut, inst->a_base, inst->a_slope);
+        break;
+        case 3:
+            inst->b_slope = *((double*)param);
+            make_sigmoid_lut(inst->b_lut, inst->b_base, inst->b_slope);
+        break;
+    }
+}
+
+void f0r_get_param_value(f0r_instance_t instance, f0r_param_t param, int param_index)
+{
+	colorenhance_t* inst = (colorenhance_t*)instance;
+	switch (param_index) 
+    {
+        case 0:
+            *((double*)param) = inst->a_base;
+        break;
+        case 1:
+            *((double*)param) = inst->b_base;
+        break;
+        case 2:
+            *((double*)param) = inst->a_slope;
+        break;
+        case 3:
+            *((double*)param) = inst->b_slope;
+        break;
+    }
+}
+
+void f0r_update(f0r_instance_t instance, double, const uint32_t* inframe, uint32_t* outframe) 
+{
+    colorenhance_t* inst = (colorenhance_t*)instance;
+    const uint8_t* input = (const uint8_t*)inframe;
+    uint8_t* output = (uint8_t*)outframe;
+
+    long size = (long)inst->width * inst->height;
+    while (size--)
+    {
+        uint8_t r, g, b;
+        ciexyz_t u;
+        oklab_t v;
+
+        u.x = gamma_expand_table[*input++];
+        u.y = gamma_expand_table[*input++];
+        u.z = gamma_expand_table[*input++];
+
+        #ifdef __SSE4_1__
+        ciexyz_to_oklab_sse4_1(&u, &v);
+        #else
+        v = ciexyz_to_oklab(u);
+        #endif
+
+        v.l = CLAMP0255(v.l);
+        v.a = inst->a_lut[CLAMP0255(v.a)];
+        v.b = inst->b_lut[CLAMP0255(v.b)];
+
+        #ifdef __SSE4_1__
+        oklab_to_ciexyz_sse4_1(&v, &u);
+        #else
+        u = oklab_to_ciexyz(v);
+        #endif
+
+        r = CLAMP0255(u.x);
+        g = CLAMP0255(u.y);
+        b = CLAMP0255(u.z);
+
+        *output++ = gamma_compress_table[r];
+        *output++ = gamma_compress_table[g];
+        *output++ = gamma_compress_table[b];
+        *output++ = *input++;
+    }
+}