Why Does `imagecreatefrompng()` Render a Black Background Instead of Transparency?

Imagecreatefrompng() Rendering Black Background Instead of Transparency

The provided PHP code for generating thumbnails using the GD library encounters an issue where PNG transparency is replaced with a solid black color. To address this problem, the code requires modifications to preserve the alpha channel information of the PNG image.

Within the cropImage() function, after the imagecreatetruecolor() call, the following modifications should be implemented:

<code class="php">switch ($stype) {

    case 'gif':
    case 'png':
        // Allocate black color and set as background
        $background = imagecolorallocate($dimg, 0, 0, 0);
        // Set black as transparent
        imagecolortransparent($dimg, $background);

        // Disable alpha blending to preserve transparency
        imagealphablending($dimg, false);

        // Enable alpha channel saving to preserve full transparency range
        imagesavealpha($dimg, true);
        break;

    default:
        break;
}</code>

These modifications ensure that the black background is removed and the PNG's transparency is preserved. The disablement of alpha blending prevents the PNG's transparent areas from being blended with the black color. The activation of alpha channel saving guarantees the retention of the complete transparency range.

By implementing these code modifications, the thumbnail generator should correctly maintain PNG transparency, rendering transparent backgrounds instead of black.

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