tests: add lcms-util with MPE curves

This adds a new test helper library that depends on LittleCMS 2.

For starters, the library implements conversion from enum transfer_fn to
ICC multiProcessingElements compatible LittleCMS curve object.

That conversion allows encoding transfer funtions in ICC files and
LittleCMS pipelines with full float32 precision instead of forcing a
conversion to a 1D LUT which for power-type curves is surprisingly
imprecise.

This also adds CI tests to make sure the conversion matches our
hand-coded transfer functions.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

tests/color_util.c

@@ -212,7 +212,7 @@ Power2_4_EOTF_inv(float o)
 	return pow(o, 1./2.4);
 }
 
-static float
+float
 apply_tone_curve(enum transfer_fn fn, float r)
 {
 	float ret = 0;

tests/color_util.h

@@ -97,6 +97,9 @@ a8r8g8b8_to_float(uint32_t v);
 bool
 find_tone_curve_type(enum transfer_fn fn, int *type, double params[5]);
 
+float
+apply_tone_curve(enum transfer_fn fn, float r);
+
 void
 process_pixel_using_pipeline(enum transfer_fn pre_curve,
 			     const struct lcmsMAT3 *mat,

tests/lcms-util-test.c

@@ -0,0 +1,85 @@
+/*
+ * Copyright 2022 Collabora, Ltd.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial
+ * portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "config.h"
+
+#include <math.h>
+#include <lcms2.h>
+
+#include "weston-test-client-helper.h"
+#include "color_util.h"
+#include "lcms_util.h"
+
+static void
+compare_pipeline_to_transfer_fn(cmsPipeline *pipeline, enum transfer_fn fn,
+				struct scalar_stat *stat)
+{
+	const unsigned N = 100000;
+	unsigned i;
+
+	for (i = 0; i < N; i++) {
+		float x = (double)i / N;
+		float ref = apply_tone_curve(fn, x);
+		float y;
+
+		cmsPipelineEvalFloat(&x, &y, pipeline);
+		scalar_stat_update(stat, y - ref, &(struct color_float){ .r = x });
+	}
+}
+
+static const enum transfer_fn build_MPE_curves_test_set[] = {
+	TRANSFER_FN_SRGB_EOTF,
+	TRANSFER_FN_SRGB_EOTF_INVERSE,
+	TRANSFER_FN_ADOBE_RGB_EOTF,
+	TRANSFER_FN_ADOBE_RGB_EOTF_INVERSE,
+	TRANSFER_FN_POWER2_4_EOTF,
+	TRANSFER_FN_POWER2_4_EOTF_INVERSE,
+};
+
+TEST_P(build_MPE_curves, build_MPE_curves_test_set)
+{
+	const enum transfer_fn *fn = data;
+	const cmsContext ctx = 0;
+	cmsToneCurve *curve;
+	cmsStage *stage;
+	cmsPipeline *pipeline;
+	struct scalar_stat stat = {};
+
+	curve = build_MPE_curve(ctx, *fn);
+	stage = cmsStageAllocToneCurves(ctx, 1, &curve);
+	cmsFreeToneCurve(curve);
+
+	pipeline = cmsPipelineAlloc(ctx, 1, 1);
+	cmsPipelineInsertStage(pipeline, cmsAT_END, stage);
+
+	compare_pipeline_to_transfer_fn(pipeline, *fn, &stat);
+	testlog("Transfer function %s as a segmented curve element, error:\n",
+		transfer_fn_name(*fn));
+	scalar_stat_print_float(&stat);
+	assert(fabs(stat.max) < 1e-7);
+	assert(fabs(stat.min) < 1e-7);
+
+	cmsPipelineFree(pipeline);
+}

tests/lcms_util.c

@@ -0,0 +1,200 @@
+/*
+ * Copyright 2022 Collabora, Ltd.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial
+ * portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "config.h"
+
+#include <math.h>
+#include <lcms2.h>
+#include <assert.h>
+
+#include "shared/helpers.h"
+#include "color_util.h"
+#include "lcms_util.h"
+
+/*
+ * MPE tone curves can only use LittleCMS parametric curve types 6-8 and not
+ * inverses.
+ * type 6: Y = (aX + b)^g + c;      params [g, a, b, c]
+ * type 7: Y = a log(bX^g + c) + d; params [g, a, b, c, d]
+ * type 8: Y = a b^(cX + d) + e;    params [a, b, c, d, e]
+ * Additionally, type 0 is sampled segment.
+ *
+ * cmsCurveSegment.x1 is the breakpoint stored in ICC files, except for the
+ * last segment. First segment always begins at -Inf, and last segment always
+ * ends at Inf.
+ */
+
+static cmsToneCurve *
+build_MPE_curve_sRGB(cmsContext ctx)
+{
+	cmsCurveSegment segments[] = {
+		{
+			/* Constant zero segment */
+			.x0 = -HUGE_VAL,
+			.x1 = 0.0,
+			.Type = 6,
+			.Params = { 1.0, 0.0, 0.0, 0.0 },
+		},
+		{
+			/* Linear segment y = x / 12.92 */
+			.x0 = 0.0,
+			.x1 = 0.04045,
+			.Type = 0,
+			.nGridPoints = 2,
+			.SampledPoints = (float[]){ 0.0, 0.04045 / 12.92 },
+		},
+		{
+			/* Power segment y = ((x + 0.055) / 1.055)^2.4
+			 * which is translated to
+			 * y = (1/1.055 * x + 0.055 / 1.055)^2.4 + 0.0
+			 */
+			.x0 = 0.04045,
+			.x1 = 1.0,
+			.Type = 6,
+			.Params = { 2.4, 1.0 / 1.055, 0.055 / 1.055, 0.0 },
+		},
+		{
+			/* Constant one segment */
+			.x0 = 1.0,
+			.x1 = HUGE_VAL,
+			.Type = 6,
+			.Params = { 1.0, 0.0, 0.0, 1.0 },
+		}
+	};
+
+	return cmsBuildSegmentedToneCurve(ctx, ARRAY_LENGTH(segments), segments);
+}
+
+static cmsToneCurve *
+build_MPE_curve_sRGB_inv(cmsContext ctx)
+{
+	cmsCurveSegment segments[] = {
+		{
+			/* Constant zero segment */
+			.x0 = -HUGE_VAL,
+			.x1 = 0.0,
+			.Type = 6,
+			.Params = { 1.0, 0.0, 0.0, 0.0 },
+		},
+		{
+			/* Linear segment y = x * 12.92 */
+			.x0 = 0.0,
+			.x1 = 0.04045 / 12.92,
+			.Type = 0,
+			.nGridPoints = 2,
+			.SampledPoints = (float[]){ 0.0, 0.04045 },
+		},
+		{
+			/* Power segment y = 1.055 * x^(1/2.4) - 0.055
+			 * which is translated to
+			 * y = (1.055^2.4 * x + 0.0)^(1/2.4) - 0.055
+			 */
+			.x0 = 0.04045 / 12.92,
+			.x1 = 1.0,
+			.Type = 6,
+			.Params = { 1.0 / 2.4, pow(1.055, 2.4), 0.0, -0.055 },
+		},
+		{
+			/* Constant one segment */
+			.x0 = 1.0,
+			.x1 = HUGE_VAL,
+			.Type = 6,
+			.Params = { 1.0, 0.0, 0.0, 1.0 },
+		}
+	};
+
+	return cmsBuildSegmentedToneCurve(ctx, ARRAY_LENGTH(segments), segments);
+}
+
+static cmsToneCurve *
+build_MPE_curve_power(cmsContext ctx, double exponent)
+{
+	cmsCurveSegment segments[] = {
+		{
+			/* Constant zero segment */
+			.x0 = -HUGE_VAL,
+			.x1 = 0.0,
+			.Type = 6,
+			.Params = { 1.0, 0.0, 0.0, 0.0 },
+		},
+		{
+			/* Power segment y = x^exponent
+			 * which is translated to
+			 * y = (1.0 * x + 0.0)^exponent + 0.0
+			 */
+			.x0 = 0.0,
+			.x1 = 1.0,
+			.Type = 6,
+			.Params = { exponent, 1.0, 0.0, 0.0 },
+		},
+		{
+			/* Constant one segment */
+			.x0 = 1.0,
+			.x1 = HUGE_VAL,
+			.Type = 6,
+			.Params = { 1.0, 0.0, 0.0, 1.0 },
+		}
+	};
+
+	return cmsBuildSegmentedToneCurve(ctx, ARRAY_LENGTH(segments), segments);
+}
+
+cmsToneCurve *
+build_MPE_curve(cmsContext ctx, enum transfer_fn fn)
+{
+	switch (fn) {
+	case TRANSFER_FN_ADOBE_RGB_EOTF:
+		return build_MPE_curve_power(ctx, 563.0 / 256.0);
+	case TRANSFER_FN_ADOBE_RGB_EOTF_INVERSE:
+		return build_MPE_curve_power(ctx, 256.0 / 563.0);
+	case TRANSFER_FN_POWER2_4_EOTF:
+		return build_MPE_curve_power(ctx, 2.4);
+	case TRANSFER_FN_POWER2_4_EOTF_INVERSE:
+		return build_MPE_curve_power(ctx, 1.0 / 2.4);
+	case TRANSFER_FN_SRGB_EOTF:
+		return build_MPE_curve_sRGB(ctx);
+	case TRANSFER_FN_SRGB_EOTF_INVERSE:
+		return build_MPE_curve_sRGB_inv(ctx);
+	default:
+		assert(0 && "unimplemented MPE curve");
+	}
+
+	return NULL;
+}
+
+cmsStage *
+build_MPE_curve_stage(cmsContext context_id, enum transfer_fn fn)
+{
+	cmsToneCurve *c;
+	cmsStage *stage;
+
+	c = build_MPE_curve(context_id, fn);
+	stage = cmsStageAllocToneCurves(context_id, 3,
+					(cmsToneCurve *[3]){ c, c, c });
+	assert(stage);
+	cmsFreeToneCurve(c);
+
+	return stage;
+}

tests/lcms_util.h

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2022 Collabora, Ltd.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial
+ * portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#pragma once
+
+#include <lcms2.h>
+
+#include "color_util.h"
+
+cmsToneCurve *
+build_MPE_curve(cmsContext ctx, enum transfer_fn fn);
+
+cmsStage *
+build_MPE_curve_stage(cmsContext context_id, enum transfer_fn fn);

tests/meson.build

@@ -60,6 +60,21 @@ dep_test_client = declare_dependency(
 	]
 )
 
+lib_lcms_util = static_library(
+	'lib_lcms_util',
+	[ 'lcms_util.c' ],
+	include_directories: common_inc,
+	dependencies: [
+		dep_lcms2, dep_libm
+	],
+	build_by_default: false,
+	install: false,
+)
+dep_lcms_util = declare_dependency(
+	link_with: lib_lcms_util,
+	dependencies: [ dep_lcms2 ]
+)
+
 exe_plugin_test = shared_library(
 	'test-plugin',
 	'weston-test.c',
@@ -243,11 +258,15 @@ if get_option('color-management-lcms')
 		error('color-management-lcms tests require lcms2 which was not found. Or, you can use \'-Dcolor-management-lcms=false\'.')
 	endif
 	tests += [
+		{	'name': 'color-metadata-parsing' },
 		{
 			'name': 'color-shaper-matrix',
 			'dep_objs': [ dep_libm, dep_lcms2 ]
 		},
-		{	'name': 'color-metadata-parsing' },
+		{
+			'name': 'lcms-util',
+			'dep_objs': [ dep_lcms_util ]
+		},
 	]
 endif