alpha_reduce

A Zig utility for converting images to greyscale with alpha channel transparency based on statistical thresholding.

What it does

• Converts colour images to greyscale
• Calculates statistical properties (mean, standard deviation) of bright pixels
• Applies adaptive thresholding using statistical analysis
• Generates alpha channel based on pixel intensity
• Outputs processed images with _t.png suffix

Usage

alpha_reduce image1.jpg image2.png image3.bmp

Processes each input file and creates corresponding *_t.png outputs.

Algorithm

1. Convert image to greyscale (average of RGB channels)
2. Calculate mean and standard deviation of pixels with brightness > 0.5
3. Set threshold as mean - 1.9 × standard_deviation
4. Normalise pixel values against threshold
5. Apply gamma correction (γ = 4.0)
6. Generate alpha channel where transparency increases with brightness

Building

Requires Zig and the zigimg library.

zig build

Dependencies

• zigimg - Image processing library for Zig