Use linear RGB

Makes things a lot easier for image manipulation algorithms which
can be expected to be applied to farbfeld data.

4 files changed, 38 insertions, 32 deletions

diff --git a/FORMAT b/FORMAT
index 6821ab2..c033efb 100644
--- a/FORMAT
+++ b/FORMAT
@@ -1,15 +1,18 @@
 
   FARBFELD IMAGE FORMAT SPECIFICATION
 
-  +--------+-------------------------------------------------------+
-  | Bytes  | Description                                           |
-  +--------+-------------------------------------------------------+
-  | 8      | "farbfeld" magic value                                |
-  +--------+-------------------------------------------------------+
-  | 4      | 32-Bit BE unsigned integer (width)                    |
-  +--------+-------------------------------------------------------+
-  | 4      | 32-Bit BE unsigned integer (height)                   |
-  +--------+-------------------------------------------------------+
-  | [2222] | 4*16-Bit BE unsigned integers [RGBA] / pixel          |
-  |        | pixels in rows, ProPhoto RGB, not alpha-premultiplied |
-  +--------+-------------------------------------------------------+
+  +--------+-----------------------------------------------+
+  | Bytes  | Description                                   |
+  +--------+-----------------------------------------------+
+  | 8      | "farbfeld" magic value                        |
+  +--------+-----------------------------------------------+
+  | 4      | 32-Bit BE unsigned integer (width)            |
+  +--------+-----------------------------------------------+
+  | 4      | 32-Bit BE unsigned integer (height)           |
+  +--------+-----------------------------------------------+
+  | [2222] | 4*16-Bit BE unsigned integers [RGBA] / pixel  |
+  |        |    - pixels in rows                           |
+  |        |    - linear ROMM RGB (ISO 22028-2:2013)       |
+  |        |         (= linear ProPhoto RGB = Melissa RGB) |
+  |        |    - no alpha premultiplication               |
+  +--------+-----------------------------------------------+
diff --git a/ff2png.c b/ff2png.c
index 9f562b8..03fa1f6 100644
--- a/ff2png.c
+++ b/ff2png.c
@@ -14,7 +14,7 @@
 
 static char *argv0;
 
-/* ProPhoto RGB */
+/* ROMM RGB primaries (ISO 22028-2:2013) */
 static cmsCIExyYTRIPLE primaries = {
 	/*     x,      y,        Y */
 	{ 0.7347, 0.2653, 0.288040 }, /* red   */
@@ -34,8 +34,8 @@ main(int argc, char *argv[])
 {
 	cmsContext icc_context;
 	cmsHPROFILE out_prof;
-	cmsMLU *mlu1, *mlu2;
-	cmsToneCurve *gamma18, *out_curve[3];
+	cmsMLU *mlu1, *mlu2, *mlu3;
+	cmsToneCurve *gamma10, *out_curve[3];
 	png_structp pngs;
 	png_infop pngi;
 	size_t png_row_len, j;
@@ -62,25 +62,27 @@ main(int argc, char *argv[])
 	width = ntohl(*((uint32_t *)(hdr + 8)));
 	height = ntohl(*((uint32_t *)(hdr + 12)));
 
-	/* icc profile (ProPhoto RGB) */
+	/* icc profile (linear ROMM RGB (ISO 22028-2:2013)) */
 	if (!(icc_context = cmsCreateContext(NULL, NULL)))
 		goto lcmserr;
-	if (!(gamma18 = cmsBuildGamma(icc_context, 1.8)))
+	if (!(gamma10 = cmsBuildGamma(icc_context, 1.0)))
 		goto lcmserr;
-	out_curve[0] = out_curve[1] = out_curve[2] = gamma18;
+	out_curve[0] = out_curve[1] = out_curve[2] = gamma10;
 	if (!(out_prof = cmsCreateRGBProfileTHR(icc_context, cmsD50_xyY(),
 	                                        &primaries, out_curve)))
 		goto lcmserr;
 	cmsSetHeaderFlags(out_prof, cmsEmbeddedProfileTrue | cmsUseAnywhere);
 	cmsSetHeaderRenderingIntent(out_prof, INTENT_RELATIVE_COLORIMETRIC);
 	cmsSetDeviceClass(out_prof, cmsSigColorSpaceClass);
-	if (!(mlu1 = cmsMLUalloc(NULL, 1)) || !(mlu2 = cmsMLUalloc(NULL, 1)))
+	if (!(mlu1 = cmsMLUalloc(NULL, 1)) || !(mlu2 = cmsMLUalloc(NULL, 1)) ||
+	    !(mlu3 = cmsMLUalloc(NULL, 1)))
 		goto lcmserr;
 	cmsMLUsetASCII(mlu1, "en", "US", "Public Domain");
 	cmsWriteTag(out_prof, cmsSigCopyrightTag, mlu1);
-	cmsMLUsetASCII(mlu2, "en", "US", "ProPhoto RGB");
-	cmsWriteTag(out_prof, cmsSigProfileDescriptionTag, mlu2);
+	cmsMLUsetASCII(mlu2, "en", "US", "aka Linear ProPhoto RGB, Melissa RGB");
 	cmsWriteTag(out_prof, cmsSigDeviceModelDescTag, mlu2);
+	cmsMLUsetASCII(mlu3, "en", "US", "Linear ROMM RGB (ISO 22028-2:2013)");
+	cmsWriteTag(out_prof, cmsSigProfileDescriptionTag, mlu3);
 	cmsSaveProfileToMem(out_prof, NULL, &icclen);
 	if (!(icc = malloc(icclen))) {
 		fprintf(stderr, "%s: malloc: out of memory\n", argv0);
@@ -101,7 +103,8 @@ main(int argc, char *argv[])
 	png_set_IHDR(pngs, pngi, width, height, 16, PNG_COLOR_TYPE_RGB_ALPHA,
 	             PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE,
 	             PNG_FILTER_TYPE_BASE);
-	png_set_iCCP(pngs, pngi, "ProPhoto RGB", 0, icc, icclen);
+	png_set_iCCP(pngs, pngi, "Linear ROMM RGB (ISO 22028-2:2013)", 0,
+	             icc, icclen);
 	png_write_info(pngs, pngi);
 
 	/* write rows */
diff --git a/jpg2ff.c b/jpg2ff.c
index c1a0f92..cdf5d56 100644
--- a/jpg2ff.c
+++ b/jpg2ff.c
@@ -12,7 +12,7 @@
 
 static char *argv0;
 
-/* ProPhoto RGB */
+/* ROMM RGB primaries (ISO 22028-2:2013) */
 static cmsCIExyYTRIPLE primaries = {
 	/*     x,      y,        Y */
 	{ 0.7347, 0.2653, 0.288040 }, /* red   */
@@ -33,7 +33,7 @@ main(int argc, char *argv[])
 {
 	cmsHPROFILE in_profile = NULL, out_profile;
 	cmsHTRANSFORM transform;
-	cmsToneCurve *gamma18, *out_curves[3];
+	cmsToneCurve *gamma10, *out_curves[3];
 	struct jpeg_decompress_struct cinfo;
 	jpeg_saved_marker_ptr marker;
 	struct jpeg_error_mgr jerr;
@@ -97,12 +97,12 @@ main(int argc, char *argv[])
 		return 1;
 	}
 
-	/* icc profile (output ProPhoto RGB) */
+	/* icc profile (output linear ROMM RGB (ISO 22028-2:2013)) */
 	if (!in_profile && !(in_profile = cmsCreate_sRGBProfile()))
 		goto lcmserr;
-	if (!(gamma18 = cmsBuildGamma(NULL, 1.8)))
+	if (!(gamma10 = cmsBuildGamma(NULL, 1.0)))
 		goto lcmserr;
-	out_curves[0] = out_curves[1] = out_curves[2] = gamma18;
+	out_curves[0] = out_curves[1] = out_curves[2] = gamma10;
 	if (!(out_profile = cmsCreateRGBProfile(cmsD50_xyY(), &primaries,
 	                                        out_curves)))
 		goto lcmserr;
diff --git a/png2ff.c b/png2ff.c
index 6750b6b..a5b96ce 100644
--- a/png2ff.c
+++ b/png2ff.c
@@ -12,7 +12,7 @@
 
 static char *argv0;
 
-/* ProPhoto RGB */
+/* ROMM RGB primaries (ISO 22028-2:2013) */
 static cmsCIExyYTRIPLE primaries = {
 	/*     x,      y,        Y */
 	{ 0.7347, 0.2653, 0.288040 }, /* red   */
@@ -32,7 +32,7 @@ main(int argc, char *argv[])
 {
 	cmsHPROFILE in_prof, out_prof;
 	cmsHTRANSFORM trans;
-	cmsToneCurve *gamma18, *out_curves[3];
+	cmsToneCurve *gamma10, *out_curves[3];
 	png_structp pngs;
 	png_infop pngi;
 	int icc_compression;
@@ -70,7 +70,7 @@ main(int argc, char *argv[])
 	height = png_get_image_height(pngs, pngi);
 	png_row_p = png_get_rows(pngs, pngi);
 
-	/* icc profile (output ProPhoto RGB) */
+	/* icc profile (output linear ROMM RGB (ISO 22028-2:2013)) */
 	if (png_get_valid(pngs, pngi, PNG_INFO_iCCP)) {
 		png_get_iCCP(pngs, pngi, &icc_name,
 		             &icc_compression, &icc_data, &icc_len);
@@ -81,9 +81,9 @@ main(int argc, char *argv[])
 		if (!(in_prof = cmsCreate_sRGBProfile()))
 			goto lcmserr;
 	}
-	if (!(gamma18 = cmsBuildGamma(NULL, 1.8)))
+	if (!(gamma10 = cmsBuildGamma(NULL, 1.0)))
 		goto lcmserr;
-	out_curves[0] = out_curves[1] = out_curves[2] = gamma18;
+	out_curves[0] = out_curves[1] = out_curves[2] = gamma10;
 	if (!(out_prof = cmsCreateRGBProfile(cmsD50_xyY(), &primaries,
 	                                        out_curves)))
 		goto lcmserr;