Using imagecolorallocatealpha() to Allocate Colors with Alpha in PHP GD
This article explains how the PHP GD function imagecolorallocatealpha() assigns colors with transparency to an image, describes its parameters and return values, and provides a complete example that creates a PNG with overlapping circles using custom alpha values.
The PHP function imagecolorallocatealpha() assigns a color with an alpha (transparency) value to an image resource, similar to imagecolorallocate() but with an extra $alpha parameter ranging from 0 (fully opaque) to 127 (fully transparent).
It returns the allocated color index on success, or FALSE (or a falsy non‑boolean) on failure.
The example creates a 300×300 true‑color image, allocates background and border colors, defines three overlapping circles with different colors and alpha levels, outputs the result as a PNG image, and finally destroys the image resource.
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