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Image

Alpha Channel

Alpha Channel (Transparency Mask)

An alpha channel stores transparency information for each pixel in an image, with values ranging from fully transparent to fully opaque. It is the fourth channel in RGBA color, enabling smooth blending of images over backgrounds.

Technical Detail

Alpha values are typically stored as 8-bit (0-255) or floating point (0.0-1.0) per pixel. Pre-multiplied alpha multiplies color values by opacity for faster compositing, while straight alpha stores them independently.

Example

```javascript
// Convert RGB to HSL
function rgbToHsl(r, g, b) {
  r /= 255; g /= 255; b /= 255;
  const max = Math.max(r, g, b), min = Math.min(r, g, b);
  const l = (max + min) / 2;
  let h = 0, s = 0;
  if (max !== min) {
    const d = max - min;
    s = l > 0.5 ? d/(2-max-min) : d/(max+min);
  }
  return [h, s, l];
}
```

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Related Terms

Alpha Compositing Aspect Ratio AVIF Batch Resize Bit Depth Canvas Channel Chroma Subsampling Chromatic Aberration Color Grading (Image) Color Profile Color Space Compression Artifact Content-Aware Fill Convolution Crop Dithering (Image) DPI DPI/PPI EXIF Feature Matching Focus Stacking Gamma Gamut Mapping HDR Histogram ICC Profile Image Histogram Image Interpolation Image Optimization Image Pyramid Image Registration Image Segmentation IPTC Lossless Compression Lossy Compression Metadata Mipmap Morphological Operations Noise Reduction (Image) Object Detection Panorama Stitching Raster Graphics Rasterization Resize Resolution Sprite Sheet Texture Atlas Thumbnail Tone Mapping Vector Graphics Vignetting WebP XMP