a lot of GREEN Color at YUV420p --> RGB in OpenGL 2.0 Shader on iOS

问题

I want to make a movie player for iOS using ffmpeg and OpenGL ES 2.0 but I have some problem. Output RGB image has a lot of GREEN color. This is code and images

480x320 width & height:
512x512 Texture width & height

I got a YUV420p row data from ffmpeg AVFrame.

    for (int i = 0, nDataLen = 0; i < 3; i++) {
        int nShift = (i == 0) ? 0 : 1;
        uint8_t *pYUVData = (uint8_t *)_frame->data[i];
        for (int j = 0; j < (mHeight >> nShift); j++) {
            memcpy(&pData->pOutBuffer[nDataLen], pYUVData, (mWidth >> nShift));
            pYUVData += _frame->linesize[i];
            nDataLen += (mWidth >> nShift);
        }
    }

and prepare texture for Y, U & V channel.

//: U Texture
    if (sampler1Texture) glDeleteTextures(1, &sampler1Texture);

    glActiveTexture(GL_TEXTURE1);
    glGenTextures(1, &sampler1Texture);
    glBindTexture(GL_TEXTURE_2D, sampler1Texture);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    // This is necessary for non-power-of-two textures
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glEnable(GL_TEXTURE_2D);

    glTexImage2D(GL_TEXTURE_2D, 
                 0, 
                 GL_LUMINANCE, 
                 texW / 2, 
                 texH / 2, 
                 0, 
                 GL_LUMINANCE, 
                 GL_UNSIGNED_BYTE,
                 NULL);

    //: V Texture
    if (sampler2Texture) glDeleteTextures(1, &sampler2Texture);

    glActiveTexture(GL_TEXTURE2);
    glGenTextures(1, &sampler2Texture);
    glBindTexture(GL_TEXTURE_2D, sampler2Texture);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    // This is necessary for non-power-of-two textures
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glEnable(GL_TEXTURE_2D);

    glTexImage2D(GL_TEXTURE_2D, 
                 0, 
                 GL_LUMINANCE, 
                 texW / 2, 
                 texH / 2, 
                 0, 
                 GL_LUMINANCE,
                 GL_UNSIGNED_BYTE,
                 NULL);

    //: Y Texture
    if (sampler0Texture) glDeleteTextures(1, &sampler0Texture);

    glActiveTexture(GL_TEXTURE0);
    glGenTextures(1, &sampler0Texture);
    glBindTexture(GL_TEXTURE_2D, sampler0Texture);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    // This is necessary for non-power-of-two textures
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glEnable(GL_TEXTURE_2D);

    glTexImage2D(GL_TEXTURE_2D, 
                 0, 
                 GL_LUMINANCE, 
                 texW, 
                 texH, 
                 0, 
                 GL_LUMINANCE,
                 GL_UNSIGNED_BYTE, 
                 NULL);

Rendering part is below.

int _idxU = mFrameW * mFrameH;
int _idxV = _idxU + (_idxU / 4);

// U data
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, sampler1Texture);
glUniform1i(sampler1Uniform, 1);

glTexSubImage2D(
                GL_TEXTURE_2D, 
                0, 
                0, 
                0, 
                mFrameW / 2,            // source width
                mFrameH / 2,            // source height
                GL_LUMINANCE,
                GL_UNSIGNED_BYTE, 
                &_frameData[_idxU]);

// V data
glActiveTexture(GL_TEXTURE2);
glBindTexture(GL_TEXTURE_2D, sampler2Texture);
glUniform1i(sampler2Texture, 2);

glTexSubImage2D(
                GL_TEXTURE_2D, 
                0, 
                0, 
                0, 
                mFrameW / 2,            // source width
                mFrameH / 2,            // source height
                GL_LUMINANCE,
                GL_UNSIGNED_BYTE,
                &_frameData[_idxV]);

// Y data
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, sampler0Texture);
glUniform1i(sampler0Uniform, 0);

glTexSubImage2D(
                GL_TEXTURE_2D, 
                0, 
                0, 
                0, 
                mFrameW,            // source width
                mFrameH,            // source height
                GL_LUMINANCE,
                GL_UNSIGNED_BYTE,
                _frameData);

Vertex Shader & Fragment Shader is below.

attribute vec4 Position;
attribute vec2 TexCoordIn;

varying vec2 TexCoordOut;
varying vec2 TexCoordOut_UV;

uniform mat4 Projection;
uniform mat4 Modelview;

void main()
{
    gl_Position = Projection * Modelview * Position;
    TexCoordOut = TexCoordIn;
}



uniform sampler2D sampler0; // Y Texture Sampler
uniform sampler2D sampler1; // U Texture Sampler
uniform sampler2D sampler2; // V Texture Sampler

varying highp vec2 TexCoordOut;

void main()
{
    highp float y = texture2D(sampler0, TexCoordOut).r;
    highp float u = texture2D(sampler2, TexCoordOut).r - 0.5;
    highp float v = texture2D(sampler1, TexCoordOut).r - 0.5;

    //y = 0.0;
    //u = 0.0;
    //v = 0.0;

    highp float r = y + 1.13983 * v;
    highp float g = y - 0.39465 * u - 0.58060 * v;
    highp float b = y + 2.03211 * u;

    gl_FragColor = vec4(r, g, b, 1.0);
}

Y Texture (Grayscale) is correct but U & V has a lot of Green Color. So final RGB image (Y+U+V) has a lot of GREEN Color. What's the problem?

Please help. thanks.

回答1:

Change u and v uniforms (vice versa) and you will have correct result.

So pixel shader (stays the same):

uniform sampler2D sampler0; // Y Texture Sampler
uniform sampler2D sampler1; // U Texture Sampler
uniform sampler2D sampler2; // V Texture Sampler

varying highp vec2 TexCoordOut;

void main()
{
    highp float y = texture2D(sampler0, TexCoordOut).r;
    highp float u = texture2D(sampler2, TexCoordOut).r - 0.5;
    highp float v = texture2D(sampler1, TexCoordOut).r - 0.5;

    highp float r = y + 1.13983 * v;
    highp float g = y - 0.39465 * u - 0.58060 * v;
    highp float b = y + 2.03211 * u;

    gl_FragColor = vec4(r, g, b, 1.0);
}

and rendering code:

// RENDERING

    int _idxU = mFrameW * mFrameH;
    int _idxV = _idxU + (_idxU / 4);

    // U data
    glActiveTexture(GL_TEXTURE1);
    glBindTexture(GL_TEXTURE_2D, sampler1Texture);

    GLint sampler1Uniform = glGetUniformLocation(programStandard, "sampler2");

    glUniform1i(sampler1Uniform, 1);

    glTexSubImage2D(
                    GL_TEXTURE_2D,
                    0,
                    0,
                    0,
                    mFrameW / 2,            // source width
                    mFrameH / 2,            // source height
                    GL_LUMINANCE,
                    GL_UNSIGNED_BYTE,
                    &_frameData[_idxU]);

    // V data
    glActiveTexture(GL_TEXTURE2);
    glBindTexture(GL_TEXTURE_2D, sampler2Texture);

    GLint sampler2Uniform = glGetUniformLocation(programStandard, "sampler1");
    glUniform1i(sampler2Uniform, 2);

    glTexSubImage2D(
                    GL_TEXTURE_2D,
                    0,
                    0,
                    0,
                    mFrameW / 2,            // source width
                    mFrameH / 2,            // source height
                    GL_LUMINANCE,
                    GL_UNSIGNED_BYTE,
                    &_frameData[_idxV]);

    // Y data
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, sampler0Texture);

    GLint sampler0Uniform = glGetUniformLocation(programStandard, "sampler0");
    glUniform1i(sampler0Uniform, 0);

    glTexSubImage2D(
                    GL_TEXTURE_2D,
                    0,
                    0,
                    0,
                    mFrameW,            // source width
                    mFrameH,            // source height
                    GL_LUMINANCE,
                    GL_UNSIGNED_BYTE,
                    _frameData);


    //draw RECT
    glVertexAttribPointer(ATTRIB_VERTEX, 3, GL_FLOAT, 0, 0, squareVertices);
    glEnableVertexAttribArray(ATTRIB_VERTEX);

    //ATTRIB_TEXTUREPOSITON
    glVertexAttribPointer(ATTRIB_TEXTUREPOSITON, 2, GL_FLOAT, 0, 0, textureCoords);
    glEnableVertexAttribArray(ATTRIB_TEXTUREPOSITON);

    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

    free(_frameData);

    [(EAGLView *)self.view presentFramebuffer];

Conclusion: u <-> v uniforms.

回答2:

Since iOS supports rgb_422 textures, Instead of using three luminance texture use one rgb_422 texture. http://www.opengl.org/registry/specs/APPLE/rgb_422.txt.

EDIT: Whoops YUV480p is different than YUV422. In this case you must convert the YUV Data to an RGB data before uploading as a texture due to its odd layout.

来源：https://stackoverflow.com/questions/11170594/a-lot-of-green-color-at-yuv420p-rgb-in-opengl-2-0-shader-on-ios

标签

ios

opengl-es

ffmpeg

yuv