[Mesa-dev] [PATCH 2/3] gallium/vl: Simplify usage of full range matrices

[Thomas Hellstrom]

When looking at the full range matrices, it becomes obvious that the difference
between the standard matrices and the full range matrices is that column 0
is multiplied by 1.164 and columns 1 and 2 are muliplied by 1.138. This can
be accomplished by multiplying the contrast with 1.164 and the saturation with
1.138/1.164. Removes the need to specify separate full range matrices.

We can also incorporate the ybias in the brightness simplifying the
calculation somewhat.

Signed-off-by: Thomas Hellstrom <thellstrom at vmware.com>
---
 src/gallium/auxiliary/vl/vl_csc.c | 50 ++++++++++-----------------------------
 1 file changed, 12 insertions(+), 38 deletions(-)

diff --git a/src/gallium/auxiliary/vl/vl_csc.c b/src/gallium/auxiliary/vl/vl_csc.c
index fc11f73..bb2cc58 100644
--- a/src/gallium/auxiliary/vl/vl_csc.c
+++ b/src/gallium/auxiliary/vl/vl_csc.c
@@ -108,18 +108,6 @@ static const vl_csc_matrix bt_601 =
 };
 
 /*
- * Converts ITU-R BT.601 YCbCr pixels to RGB pixels where:
- * Y is in [16,235], Cb and Cr are in [16,240]
- * R, G, and B are in [0,255]
- */
-static const vl_csc_matrix bt_601_full =
-{
-   { 1.164f,  0.0f,    1.596f, 0.0f, },
-   { 1.164f, -0.391f, -0.813f, 0.0f, },
-   { 1.164f,  2.018f,  0.0f,   0.0f, }
-};
-
-/*
  * Converts ITU-R BT.709 YCbCr pixels to RGB pixels where:
  * Y is in [16,235], Cb and Cr are in [16,240]
  * R, G, and B are in [16,235]
@@ -131,18 +119,6 @@ static const vl_csc_matrix bt_709 =
    { 1.0f,  1.816f,  0.0f,   0.0f, }
 };
 
-/*
- * Converts ITU-R BT.709 YCbCr pixels to RGB pixels where:
- * Y is in [16,235], Cb and Cr are in [16,240]
- * R, G, and B are in [0,255]
- */
-static const vl_csc_matrix bt_709_full =
-{
-   { 1.164f,  0.0f,    1.793f, 0.0f, },
-   { 1.164f, -0.213f, -0.534f, 0.0f, },
-   { 1.164f,  2.115f,  0.0f,   0.0f, }
-};
-
 static const vl_csc_matrix smpte240m =
 {
    { 1.0f,  0.0f,    1.582f, 0.0f, },
@@ -150,13 +126,6 @@ static const vl_csc_matrix smpte240m =
    { 1.0f,  1.833f,  0.0f,   0.0f, }
 };
 
-static const vl_csc_matrix smpte240m_full =
-{
-   { 1.164f,  0.0f,    1.794f, 0.0f, },
-   { 1.164f, -0.258f, -0.543f, 0.0f, },
-   { 1.164f,  2.079f,  0.0f,   0.0f, }
-};
-
 static const vl_csc_matrix identity =
 {
    { 1.0f, 0.0f, 0.0f, 0.0f, },
@@ -176,7 +145,6 @@ void vl_csc_get_matrix(enum VL_CSC_COLOR_STANDARD cs,
                        bool full_range,
                        vl_csc_matrix *matrix)
 {
-   float ybias = full_range ? -16.0f/255.0f : 0.0f;
    float cbbias = -128.0f/255.0f;
    float crbias = -128.0f/255.0f;
 
@@ -188,17 +156,23 @@ void vl_csc_get_matrix(enum VL_CSC_COLOR_STANDARD cs,
 
    const vl_csc_matrix *cstd;
 
+   if (full_range) {
+      b -= -16.0f/255.0f; /* Adjust for the y bias */
+      c *= 1.164f;        /* Adjust for the y range */
+      s *= 1.138f/1.164f; /* Adjust for the chroma range */
+   }
+
    assert(matrix);
 
    switch (cs) {
       case VL_CSC_COLOR_STANDARD_BT_601:
-         cstd = full_range ? &bt_601_full : &bt_601;
+         cstd = &bt_601;
          break;
       case VL_CSC_COLOR_STANDARD_BT_709:
-         cstd = full_range ? &bt_709_full : &bt_709;
+         cstd = &bt_709;
          break;
       case VL_CSC_COLOR_STANDARD_SMPTE_240M:
-         cstd = full_range ? &smpte240m_full : &smpte240m;
+         cstd = &smpte240m;
          break;
       case VL_CSC_COLOR_STANDARD_IDENTITY:
       default:
@@ -210,21 +184,21 @@ void vl_csc_get_matrix(enum VL_CSC_COLOR_STANDARD cs,
    (*matrix)[0][0] = c * (*cstd)[0][0];
    (*matrix)[0][1] = c * (*cstd)[0][1] * s * cosf(h) - c * (*cstd)[0][2] * s * sinf(h);
    (*matrix)[0][2] = c * (*cstd)[0][2] * s * cosf(h) + c * (*cstd)[0][1] * s * sinf(h);
-   (*matrix)[0][3] = (*cstd)[0][3] + (*cstd)[0][0] * c * (b + ybias) +
+   (*matrix)[0][3] = (*cstd)[0][3] + (*cstd)[0][0] * c * b +
                      (*cstd)[0][1] * (c * cbbias * s * cosf(h) + c * crbias * s * sinf(h)) +
                      (*cstd)[0][2] * (c * crbias * s * cosf(h) - c * cbbias * s * sinf(h));
 
    (*matrix)[1][0] = c * (*cstd)[1][0];
    (*matrix)[1][1] = c * (*cstd)[1][1] * s * cosf(h) - c * (*cstd)[1][2] * s * sinf(h);
    (*matrix)[1][2] = c * (*cstd)[1][2] * s * cosf(h) + c * (*cstd)[1][1] * s * sinf(h);
-   (*matrix)[1][3] = (*cstd)[1][3] + (*cstd)[1][0] * c * (b + ybias) +
+   (*matrix)[1][3] = (*cstd)[1][3] + (*cstd)[1][0] * c * b +
                      (*cstd)[1][1] * (c * cbbias * s * cosf(h) + c * crbias * s * sinf(h)) +
                      (*cstd)[1][2] * (c * crbias * s * cosf(h) - c * cbbias * s * sinf(h));
 
    (*matrix)[2][0] = c * (*cstd)[2][0];
    (*matrix)[2][1] = c * (*cstd)[2][1] * s * cosf(h) - c * (*cstd)[2][2] * s * sinf(h);
    (*matrix)[2][2] = c * (*cstd)[2][2] * s * cosf(h) + c * (*cstd)[2][1] * s * sinf(h);
-   (*matrix)[2][3] = (*cstd)[2][3] + (*cstd)[2][0] * c * (b + ybias) +
+   (*matrix)[2][3] = (*cstd)[2][3] + (*cstd)[2][0] * c * b +
                      (*cstd)[2][1] * (c * cbbias * s * cosf(h) + c * crbias * s * sinf(h)) +
                      (*cstd)[2][2] * (c * crbias * s * cosf(h) - c * cbbias * s * sinf(h));
 }
-- 
2.5.0