Alpha premul pipeline cleanup

This assumptions are now made:
- Internally float buffers are always linear alpha-premul colors
- Readers should worry about delivering float buffers with that
  assumptions.
- There's an input image setting to say whether it's stored with
  straight/premul alpha on the disk.
- Byte buffers are now assumed have straight alpha, readers should
  deliver straight alpha.

Some implementation details:

- Removed scene's color unpremultiply setting, which was very
  much confusing and was wrong for default settings.
  Now all renderers assumes to deliver premultiplied alpha.

- IMB_buffer_byte_from_float will now linearize alpha when
  converting from buffer.

- Sequencer's effects were changed to assume bytes have got
  straight alpha. Most of effects will work with bytes still,
  however for glow it was more tricky to avoid data loss, so
  there's a commented out glow implementation which converts
  byte buffer to floats first, operates on floats and returns
  bytes back. It's slower and not sure if it should actually
  be used -- who're using glow on alpha anyway?

- Sequencer modifiers should also be working nice with straight
  bytes now.

- GLSL preview will predivide float textures to make nice shading,
  shading with byte textures worked nice (GLSL was assuming straight
  alpha).

- Blender Internal will set alpha=1 to the whole sky. The same
  happens in Cycles and there's no way to avoid this -- sky is
  neither straight nor premul and doesn't fit color pipeline well.

- Straight alpha mode for render result was also eliminated.

- Conversion to correct alpha need to be done before linearizing
  float buffer.

- TIFF will now load and save files with proper alpha mode setting
  in file meta data header.

- Remove Use Alpha from texture mapping and replaced with image
  datablock setting.

  Behaves much more predictable and clear from code point of view
  and solves possible regressions when non-premultiplied images were
  used as textures with ignoring alpha channel.

1 files changed, 39 insertions, 20 deletions

diff --git a/source/blender/blenkernel/intern/image.c b/source/blender/blenkernel/intern/image.c
index 8630ace4edf..b93f917c9e2 100644
--- a/source/blender/blenkernel/intern/image.c
+++ b/source/blender/blenkernel/intern/image.c
@@ -312,10 +312,6 @@ static void image_assign_ibuf(Image *ima, ImBuf *ibuf, int index, int frame)
 				break;
 
 		ibuf->index = index;
-		if (ima->flag & IMA_CM_PREDIVIDE)
-			ibuf->flags |= IB_cm_predivide;
-		else
-			ibuf->flags &= ~IB_cm_predivide;
 
 		/* this function accepts (link == NULL) */
 		BLI_insertlinkbefore(&ima->ibufs, link, ibuf);
@@ -552,6 +548,26 @@ int BKE_image_scale(Image *image, int width, int height)
 	return (ibuf != NULL);
 }
 
+static void image_init_color_management(Image *ima)
+{
+	ImBuf *ibuf;
+	char name[FILE_MAX];
+
+	BKE_image_user_file_path(NULL, ima, name);
+
+	/* will set input color space to image format default's */
+	ibuf = IMB_loadiffname(name, IB_test | IB_alphamode_detect, ima->colorspace_settings.name);
+
+	if (ibuf) {
+		if (ibuf->flags & IB_alphamode_premul)
+			ima->alpha_mode = IMA_ALPHA_PREMUL;
+		else
+			ima->alpha_mode = IMA_ALPHA_STRAIGHT;
+
+		IMB_freeImBuf(ibuf);
+	}
+}
+
 Image *BKE_image_load(const char *filepath)
 {
 	Image *ima;
@@ -579,6 +595,8 @@ Image *BKE_image_load(const char *filepath)
 	if (BLI_testextensie_array(filepath, imb_ext_movie))
 		ima->source = IMA_SRC_MOVIE;
 
+	image_init_color_management(ima);
+
 	return ima;
 }
 
@@ -666,7 +684,7 @@ static ImBuf *add_ibuf_size(unsigned int width, unsigned int height, const char
 		/* both byte and float buffers are filling in sRGB space, need to linearize float buffer after BKE_image_buf_fill* functions */
 
 		IMB_buffer_float_from_float(rect_float, rect_float, ibuf->channels, IB_PROFILE_LINEAR_RGB, IB_PROFILE_SRGB,
-		                            ibuf->flags & IB_cm_predivide, ibuf->x, ibuf->y, ibuf->x, ibuf->x);
+		                            TRUE, ibuf->x, ibuf->y, ibuf->x, ibuf->x);
 	}
 
 	return ibuf;
@@ -2343,7 +2361,7 @@ void BKE_image_backup_render(Scene *scene, Image *ima)
 static void image_create_multilayer(Image *ima, ImBuf *ibuf, int framenr)
 {
 	const char *colorspace = ima->colorspace_settings.name;
-	int predivide = ima->flag & IMA_CM_PREDIVIDE;
+	int predivide = ima->alpha_mode == IMA_ALPHA_PREMUL;
 
 	ima->rr = RE_MultilayerConvert(ibuf->userdata, colorspace, predivide, ibuf->x, ibuf->y);
 
@@ -2375,6 +2393,18 @@ static void image_initialize_after_load(Image *ima, ImBuf *ibuf)
 
 }
 
+static int imbuf_alpha_flags_for_image(Image *ima)
+{
+	int flag = 0;
+
+	if (ima->flag & IMA_IGNORE_ALPHA)
+		flag |= IB_ignore_alpha;
+	else if (ima->alpha_mode == IMA_ALPHA_PREMUL)
+		flag |= IB_alphamode_premul;
+
+	return flag;
+}
+
 static ImBuf *image_load_sequence_file(Image *ima, ImageUser *iuser, int frame)
 {
 	struct ImBuf *ibuf;
@@ -2389,8 +2419,7 @@ static ImBuf *image_load_sequence_file(Image *ima, ImageUser *iuser, int frame)
 	BKE_image_user_file_path(iuser, ima, name);
 
 	flag = IB_rect | IB_multilayer;
-	if (ima->flag & IMA_DO_PREMUL)
-		flag |= IB_premul;
+	flag |= imbuf_alpha_flags_for_image(ima);
 
 	/* read ibuf */
 	ibuf = IMB_loadiffname(name, flag, ima->colorspace_settings.name);
@@ -2549,15 +2578,14 @@ static ImBuf *image_load_image_file(Image *ima, ImageUser *iuser, int cfra)
 	/* is there a PackedFile with this image ? */
 	if (ima->packedfile) {
 		flag = IB_rect | IB_multilayer;
-		if (ima->flag & IMA_DO_PREMUL) flag |= IB_premul;
+		flag |= imbuf_alpha_flags_for_image(ima);
 
 		ibuf = IMB_ibImageFromMemory((unsigned char *)ima->packedfile->data, ima->packedfile->size, flag,
 		                             ima->colorspace_settings.name, "<packed data>");
 	}
 	else {
 		flag = IB_rect | IB_multilayer | IB_metadata;
-		if (ima->flag & IMA_DO_PREMUL)
-			flag |= IB_premul;
+		flag |= imbuf_alpha_flags_for_image(ima);
 
 		/* get the right string */
 		BKE_image_user_frame_calc(iuser, cfra, 0);
@@ -2777,15 +2805,6 @@ static ImBuf *image_get_render_result(Image *ima, ImageUser *iuser, void **lock_
 
 	ibuf->dither = dither;
 
-	if (iuser->scene->r.color_mgt_flag & R_COLOR_MANAGEMENT_PREDIVIDE) {
-		ibuf->flags |= IB_cm_predivide;
-		ima->flag |= IMA_CM_PREDIVIDE;
-	}
-	else {
-		ibuf->flags &= ~IB_cm_predivide;
-		ima->flag &= ~IMA_CM_PREDIVIDE;
-	}
-
 	ima->ok = IMA_OK_LOADED;
 
 	return ibuf;