6 #include "ycbcr_input.h"
10 using namespace Eigen;
14 // OpenGL has texel center in (0.5, 0.5), but different formats have
15 // chroma in various other places. If luma samples are X, the chroma
16 // sample is *, and subsampling is 3x3, the situation with chroma
17 // center in (0.5, 0.5) looks approximately like this:
23 // If, on the other hand, chroma center is in (0.0, 0.5) (common
24 // for e.g. MPEG-4), the figure changes to:
30 // In other words, (0.0, 0.0) means that the chroma sample is exactly
31 // co-sited on top of the top-left luma sample. Note, however, that
32 // this is _not_ 0.5 texels to the left, since the OpenGL's texel center
33 // is in (0.5, 0.5); it is in (0.25, 0.25). In a sense, the four luma samples
34 // define a square where chroma position (0.0, 0.0) is in texel position
35 // (0.25, 0.25) and chroma position (1.0, 1.0) is in texel position (0.75, 0.75)
36 // (the outer border shows the borders of the texel itself, ie. from
47 // Also note that if we have no subsampling, the square will have zero
48 // area and the chroma position does not matter at all.
49 float compute_chroma_offset(float pos, unsigned subsampling_factor, unsigned resolution)
51 float local_chroma_pos = (0.5 + pos * (subsampling_factor - 1)) / subsampling_factor;
52 return (0.5 - local_chroma_pos) / resolution;
57 YCbCrInput::YCbCrInput(const ImageFormat &image_format,
58 const YCbCrFormat &ycbcr_format,
59 unsigned width, unsigned height)
60 : image_format(image_format),
61 ycbcr_format(ycbcr_format),
63 needs_pbo_recreate(false),
69 pbos[0] = pbos[1] = pbos[2] = 0;
70 texture_num[0] = texture_num[1] = texture_num[2] = 0;
72 assert(width % ycbcr_format.chroma_subsampling_x == 0);
73 pitch[0] = widths[0] = width;
74 pitch[1] = widths[1] = width / ycbcr_format.chroma_subsampling_x;
75 pitch[2] = widths[2] = width / ycbcr_format.chroma_subsampling_x;
77 assert(height % ycbcr_format.chroma_subsampling_y == 0);
79 heights[1] = height / ycbcr_format.chroma_subsampling_y;
80 heights[2] = height / ycbcr_format.chroma_subsampling_y;
82 register_int("needs_mipmaps", &needs_mipmaps);
85 YCbCrInput::~YCbCrInput()
88 glDeleteBuffers(3, pbos);
91 if (texture_num[0] != 0) {
92 glDeleteTextures(3, texture_num);
97 void YCbCrInput::finalize()
99 glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
102 // Create PBOs to hold the textures holding the input image, and then the texture itself.
103 glGenBuffers(3, pbos);
105 glGenTextures(3, texture_num);
108 for (unsigned channel = 0; channel < 3; ++channel) {
109 glBindBuffer(GL_PIXEL_UNPACK_BUFFER_ARB, pbos[channel]);
111 glBufferData(GL_PIXEL_UNPACK_BUFFER_ARB, pitch[channel] * heights[channel], NULL, GL_STREAM_DRAW);
113 glBindBuffer(GL_PIXEL_UNPACK_BUFFER_ARB, 0);
116 glBindTexture(GL_TEXTURE_2D, texture_num[channel]);
118 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
120 glPixelStorei(GL_UNPACK_ROW_LENGTH, pitch[channel]);
122 glTexImage2D(GL_TEXTURE_2D, 0, GL_LUMINANCE8, widths[channel], heights[channel], 0, GL_LUMINANCE, GL_UNSIGNED_BYTE, NULL);
124 glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
132 void YCbCrInput::set_gl_state(GLuint glsl_program_num, const std::string& prefix, unsigned *sampler_num)
134 for (unsigned channel = 0; channel < 3; ++channel) {
135 glActiveTexture(GL_TEXTURE0 + *sampler_num + channel);
137 glBindTexture(GL_TEXTURE_2D, texture_num[channel]);
140 if (needs_update || needs_pbo_recreate) {
141 // Copy the pixel data into the PBO.
142 glBindBuffer(GL_PIXEL_UNPACK_BUFFER_ARB, pbos[channel]);
145 if (needs_pbo_recreate) {
146 // The pitch has changed; we need to reallocate this PBO.
147 glBufferData(GL_PIXEL_UNPACK_BUFFER_ARB, pitch[channel] * heights[channel], NULL, GL_STREAM_DRAW);
151 void *mapped_pbo = glMapBufferARB(GL_PIXEL_UNPACK_BUFFER_ARB, GL_WRITE_ONLY);
152 memcpy(mapped_pbo, pixel_data[channel], pitch[channel] * heights[channel]);
154 glUnmapBufferARB(GL_PIXEL_UNPACK_BUFFER_ARB);
157 // Re-upload the texture from the PBO.
158 glPixelStorei(GL_UNPACK_ROW_LENGTH, pitch[channel]);
160 glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, widths[channel], heights[channel], GL_LUMINANCE, GL_UNSIGNED_BYTE, BUFFER_OFFSET(0));
162 glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
164 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
166 glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
168 glBindBuffer(GL_PIXEL_UNPACK_BUFFER_ARB, 0);
174 set_uniform_int(glsl_program_num, prefix, "tex_y", *sampler_num + 0);
175 set_uniform_int(glsl_program_num, prefix, "tex_cb", *sampler_num + 1);
176 set_uniform_int(glsl_program_num, prefix, "tex_cr", *sampler_num + 2);
179 needs_update = false;
180 needs_pbo_recreate = false;
183 std::string YCbCrInput::output_fragment_shader()
185 float coeff[3], offset[3], scale[3];
187 switch (ycbcr_format.luma_coefficients) {
196 // Rec. 709, page 19.
205 if (ycbcr_format.full_range) {
206 offset[0] = 0.0 / 255.0;
207 offset[1] = 128.0 / 255.0;
208 offset[2] = 128.0 / 255.0;
214 // Rec. 601, page 4; Rec. 709, page 19.
215 offset[0] = 16.0 / 255.0;
216 offset[1] = 128.0 / 255.0;
217 offset[2] = 128.0 / 255.0;
219 scale[0] = 255.0 / 219.0;
220 scale[1] = 255.0 / 224.0;
221 scale[2] = 255.0 / 224.0;
224 // Matrix to convert RGB to YCbCr. See e.g. Rec. 601.
225 Matrix3d rgb_to_ycbcr;
226 rgb_to_ycbcr(0,0) = coeff[0];
227 rgb_to_ycbcr(0,1) = coeff[1];
228 rgb_to_ycbcr(0,2) = coeff[2];
230 float cb_fac = (224.0 / 219.0) / (coeff[0] + coeff[1] + 1.0f - coeff[2]);
231 rgb_to_ycbcr(1,0) = -coeff[0] * cb_fac;
232 rgb_to_ycbcr(1,1) = -coeff[1] * cb_fac;
233 rgb_to_ycbcr(1,2) = (1.0f - coeff[2]) * cb_fac;
235 float cr_fac = (224.0 / 219.0) / (1.0f - coeff[0] + coeff[1] + coeff[2]);
236 rgb_to_ycbcr(2,0) = (1.0f - coeff[0]) * cr_fac;
237 rgb_to_ycbcr(2,1) = -coeff[1] * cr_fac;
238 rgb_to_ycbcr(2,2) = -coeff[2] * cr_fac;
240 // Inverting the matrix gives us what we need to go from YCbCr back to RGB.
241 Matrix3d ycbcr_to_rgb = rgb_to_ycbcr.inverse();
243 std::string frag_shader;
245 frag_shader = output_glsl_mat3("PREFIX(inv_ycbcr_matrix)", ycbcr_to_rgb);
248 sprintf(buf, "const vec3 PREFIX(offset) = vec3(%.8f, %.8f, %.8f);\n",
249 offset[0], offset[1], offset[2]);
252 sprintf(buf, "const vec3 PREFIX(scale) = vec3(%.8f, %.8f, %.8f);\n",
253 scale[0], scale[1], scale[2]);
256 float cb_offset_x = compute_chroma_offset(
257 ycbcr_format.cb_x_position, ycbcr_format.chroma_subsampling_x, widths[1]);
258 float cb_offset_y = compute_chroma_offset(
259 ycbcr_format.cb_y_position, ycbcr_format.chroma_subsampling_y, heights[1]);
260 sprintf(buf, "const vec2 PREFIX(cb_offset) = vec2(%.8f, %.8f);\n",
261 cb_offset_x, cb_offset_y);
264 float cr_offset_x = compute_chroma_offset(
265 ycbcr_format.cr_x_position, ycbcr_format.chroma_subsampling_x, widths[2]);
266 float cr_offset_y = compute_chroma_offset(
267 ycbcr_format.cr_y_position, ycbcr_format.chroma_subsampling_y, heights[2]);
268 sprintf(buf, "const vec2 PREFIX(cr_offset) = vec2(%.8f, %.8f);\n",
269 cr_offset_x, cr_offset_y);
272 frag_shader += read_file("ycbcr_input.frag");