Convert PNG Image to 16-Color Palette with PHP

This code loads an input PNG image, converts it to a 16-color palette image using the 'imagetruecolortopalette()' function, and then saves the output as a new PNG image named 'output.png'. The 'false' parameter in the 'imagetruecolortopalette()' function indicates that the palette should be generated using the most frequently used colors in the image.