如何在Android OpenGL中实现亮度与对比度合一滤镜

Got it! Combining brightness and contrast into a single filter is a great way to keep your code streamlined while letting both parameters work independently. Here's a complete, modified implementation that does exactly that:

Full Filter Class Code #

public class GlBrightnessContrastFilter extends GlFilter {
    private static final String FRAGMENT_SHADER = "" +
            "precision mediump float;" +
            " varying vec2 vTextureCoord;\n" +
            " \n" +
            " uniform lowp sampler2D sTexture;\n" +
            " uniform lowp float brightness;\n" +
            " uniform lowp float contrast;\n" +
            " \n" +
            " void main()\n" +
            " {\n" +
            " lowp vec4 textureColor = texture2D(sTexture, vTextureCoord);\n" +
            " \n" +
            " // First adjust contrast, then brightness to keep parameters independent\n" +
            " lowp vec3 adjustedColor = ((textureColor.rgb - vec3(0.5)) * contrast + vec3(0.5));\n" +
            " adjustedColor += vec3(brightness);\n" +
            " \n" +
            " gl_FragColor = vec4(adjustedColor, textureColor.w);\n" +
            " }";

    private float brightness = 0f;
    private float contrast = 1f; // Default: no contrast change

    public GlBrightnessContrastFilter() {
        super(DEFAULT_VERTEX_SHADER, FRAGMENT_SHADER);
    }

    public void setBrightness(float brightness) {
        this.brightness = brightness;
    }

    public void setContrast(float contrast) {
        this.contrast = contrast;
    }

    @Override
    public void onDraw() {
        // Pass both parameters to the shader
        GLES20.glUniform1f(getHandle("brightness"), this.brightness);
        GLES20.glUniform1f(getHandle("contrast"), this.contrast);
    }
}

Key Changes Explained #

1. Fragment Shader Updates #

• Added the contrast uniform variable alongside brightness
• Adjusted the color calculation order:
  • First handle contrast by shifting colors around the neutral gray value (0.5), multiplying by the contrast factor, then shifting back. This ensures contrast adjustments don't alter the base brightness level.
  • Then add the brightness offset to the contrast-adjusted color, keeping both effects independent.

2. Java Class Updates #

• Renamed the class to GlBrightnessContrastFilter to reflect its new functionality
• Added a contrast member variable with a default value of 1.0 (which means no contrast change initially)
• Implemented the setContrast() setter method to update the contrast parameter
• Updated the onDraw() method to pass both the brightness and contrast values to the shader using glUniform1f()

Parameter Range Recommendations #

• Brightness: Stick to values between -1.0 (full black) and 1.0 (full white). 0.0 is the original image brightness.
• Contrast: Use values between 0.0 (flat gray image) and 2.0 (high contrast). 1.0 maintains the original image contrast.

内容的提问来源于stack exchange，提问作者Aadi