Android GPUImage-13: Sepia

1.效果图

2.shader

"attribute vec4 position;\n" +
            "attribute vec4 inputTextureCoordinate;\n" +
            "\n" +
            "uniform float imageWidthFactor; \n" +
            "uniform float imageHeightFactor; \n" +
            "uniform float sharpness;\n" +
            "\n" +
            "varying vec2 textureCoordinate;\n" +
            "varying vec2 leftTextureCoordinate;\n" +
            "varying vec2 rightTextureCoordinate; \n" +
            "varying vec2 topTextureCoordinate;\n" +
            "varying vec2 bottomTextureCoordinate;\n" +
            "\n" +
            "varying float centerMultiplier;\n" +
            "varying float edgeMultiplier;\n" +
            "\n" +
            "void main()\n" +
            "{\n" +
            "    gl_Position = position;\n" +
            "    \n" +
            "    mediump vec2 widthStep = vec2(imageWidthFactor, 0.0);\n" +
            "    mediump vec2 heightStep = vec2(0.0, imageHeightFactor);\n" +
            "    \n" +
            "    textureCoordinate = inputTextureCoordinate.xy;\n" +
            "    leftTextureCoordinate = inputTextureCoordinate.xy - widthStep;\n" +
            "    rightTextureCoordinate = inputTextureCoordinate.xy + widthStep;\n" +
            "    topTextureCoordinate = inputTextureCoordinate.xy + heightStep;     \n" +
            "    bottomTextureCoordinate = inputTextureCoordinate.xy - heightStep;\n" +
            "    \n" +
            "    centerMultiplier = 1.0 + 4.0 * sharpness;\n" +
            "    edgeMultiplier = sharpness;\n" +
            "}";

 

static final String SHARPEN_FRAGMENT_SHADER = "" +
            "precision highp float;\n" +
            "\n" +
            "varying highp vec2 textureCoordinate;\n" +
            "varying highp vec2 leftTextureCoordinate;\n" +
            "varying highp vec2 rightTextureCoordinate; \n" +
            "varying highp vec2 topTextureCoordinate;\n" +
            "varying highp vec2 bottomTextureCoordinate;\n" +
            "\n" +
            "varying highp float centerMultiplier;\n" +
            "varying highp float edgeMultiplier;\n" +
            "\n" +
            "uniform sampler2D inputImageTexture;\n" +
            "\n" +
            "void main()\n" +
            "{\n" +
            "    mediump vec3 textureColor = texture2D(inputImageTexture, textureCoordinate).rgb;\n" +
            "    mediump vec3 leftTextureColor = texture2D(inputImageTexture, leftTextureCoordinate).rgb;\n" +
            "    mediump vec3 rightTextureColor = texture2D(inputImageTexture, rightTextureCoordinate).rgb;\n" +
            "    mediump vec3 topTextureColor = texture2D(inputImageTexture, topTextureCoordinate).rgb;\n" +
            "    mediump vec3 bottomTextureColor = texture2D(inputImageTexture, bottomTextureCoordinate).rgb;\n" +
            "\n" +
            "    gl_FragColor = vec4((textureColor * centerMultiplier - (leftTextureColor * edgeMultiplier + rightTextureColor * edgeMultiplier + topTextureColor * edgeMultiplier + bottomTextureColor * edgeMultiplier)), texture2D(inputImageTexture, bottomTextureCoordinate).w);\n" +
            "}";

3.原理

取上下左右四个点，把中心点的像素按照一定的sharpness来改变，临近的像素是比较相似的。