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Fix transparency case in DVB-SUB. 

This fixes some math errors in the color conversions and handles the
case of Y=0.

Fixes #903

Change-Id: I796246e4d62a3161b44916f97e9e98f9203ad338
This commit is contained in:
Jacob Trimble 2021-03-23 12:04:07 -07:00
parent aa046a8d9e
commit c1f64e5350
1 changed files with 10 additions and 2 deletions
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12
packager/media/formats/dvb/dvb_sub_parser.cc
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@ -6,6 +6,8 @@
#include "packager/media/formats/dvb/dvb_sub_parser.h"
#include <algorithm>
#include "packager/base/logging.h"
#include "packager/media/formats/mp2t/mp2t_common.h"
@ -15,9 +17,15 @@ namespace media {
namespace {
RgbaColor ConvertYuv(uint8_t Y, uint8_t Cr, uint8_t Cb, uint8_t T) {
// Converts based on ITU-R BT.601.
// See https://en.wikipedia.org/wiki/YCbCr
//
// Note that the T value should be interpolated based on a full transparency
// being 256. This means that T=255 should not be fully transparent. Y=0 is
// used to signal full transparency.
// Values for Y<16 (except Y=0) are invalid, so clamp to 16.
RgbaColor color;
const double y_transform = 255.0 / 219 * (Y - 16);
const double y_transform = 255.0 / 219 * (std::max<uint8_t>(Y, 16) - 16);
const double cb_transform = 255.0 / 244 * 1.772 * (Cb - 128);
const double cr_transform = 255.0 / 244 * 1.402 * (Cr - 128);
const double f1 = 0.114 / 0.587;
@ -26,7 +34,7 @@ RgbaColor ConvertYuv(uint8_t Y, uint8_t Cr, uint8_t Cb, uint8_t T) {
color.g =
static_cast<uint8_t>(y_transform - cb_transform * f1 - cr_transform * f2);
color.b = static_cast<uint8_t>(y_transform + cb_transform);
color.a = 255 - T;
color.a = Y == 0 ? 0 : (T == 0 ? 255 : 256 - T);
return color;
}