varying highp vec2 textureCoordinate;

uniform sampler2D inputImageTexture;
uniform lowp float contrast;

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