varying highp vec2 textureCoordinate; uniform sampler2D inputImageTexture; void main() { lowp vec4 textureColor = texture2D(inputImageTexture, textureCoordinate); lowp vec4 outputColor; outputColor.r = (textureColor.r * 0.393) + (textureColor.g * 0.769) + (textureColor.b * 0.189); ...