Contrast Shader (GPUImage)

ContrastShader.fsh

varying vec2 textureCoordinate;

uniform sampler2D inputImageTexture;
uniform float contrast;

void main()
{
    vec4 textureColor = texture2D(inputImageTexture, textureCoordinate);
    
    gl_FragColor = vec4(((textureColor.rgb - vec3(0.5)) * contrast + vec3(0.5)), textureColor.w);
}