Some minor comment fixes in ycbcr.h.

[movit] / ycbcr.h

diff --git a/ycbcr.h b/ycbcr.h
index 4eb9e73185794fc0118ec2590e4303892dfa8595..6f9f4c9d3ac6b25e880c2931e439c3549688694e 100644 (file)
--- a/ycbcr.h
+++ b/ycbcr.h
@@ -21,7 +21,7 @@
 // framebuffer, ie., the range [0.0,1.0] maps to [0,255] for 8-bit
 // and to [0,1023] (or [0_d,255.75_d] in BT.601 parlance) for 10-bit.
 //
-// BT.701 (page 5) seems to agree with BT.601; it specifies range 16–235 for
+// BT.709 (page 5) seems to agree with BT.601; it specifies range 16–235 for
 // 8-bit luma, and 64–940 for 10-bit luma. This would indicate, for a GPU,
 // that that for 8-bit mode, the range would be 16/255 to 235/255
 // (0.06275 to 0.92157), while for 10-bit, it should be 64/1023 to 940/1023
@@ -29,9 +29,13 @@
 // range, 10-bit goes out of range (white gets to 942), while if you select
 // 10-bit range, 8-bit gets only to 234, making true white impossible.
 //
-// We currently support the 8-bit ranges only, since all of our Y'CbCr
-// handling effects happen to support only 8-bit at the moment. We will need
-// to fix this eventually, though, with an added field to YCbCrFormat.
+// Thus, you will need to specify the actual precision of the Y'CbCr source
+// (or destination); the num_levels field is the right place. Most people
+// will want to simply set this to 256, as 8-bit Y'CbCr is the most common,
+// but the right value will naturally depend on your input.
+//
+// We could use unsigned formats (e.g. GL_R8UI), which in a sense would
+// solve all of this, but then we'd lose filtering.
 
 #include "image_format.h"
 
@@ -48,8 +52,8 @@ struct YCbCrFormat {
        // JPEG uses the Rec. 601 luma coefficients, but full range.
        bool full_range;
 
-       // Currently unused, but should be set to 256 for future expansion,
-       // indicating 8-bit interpretation (see file-level comment).
+       // Set to 2^n for n-bit Y'CbCr (e.g. 256 for 8-bit Y'CbCr).
+       // See file-level comment.
        int num_levels;
 
        // Sampling factors for chroma components. For no subsampling (4:4:4),