Question

I have a jpeg image resource loaded into a variable in php. Given a grayscale value, like 6, how can I set a single, particular pixel to that grayscale value? My client has made it exceedingly clear that there is a big difference between grayscale and rgb.

Is this even doable in php with the GD library? If so, how?

Note: The script does indeed grayscale the entire image, but using an obscure algorithm. My script obtains the RGB for each pixel, and obtains the grayscale value corresponding to the algorithm. It just needs to now transform that pixel to that particular grayscale value.

Answer 1

You will probably find the the imagesetpixel function handy. The following is an example of how you could use it:

// $image = <GD image resource>

for($x = 0; $x < $width; x++)
{
    for($y = 0; $y < $height; $y++)
    {
        $value = specialFunction($rgb_value);
        // Depending on what the above function returns, the call below
        // might have to be changed
        $color = imagecolorallocate($image, $value, $value, $value);
        imagesetpixel($image, $x, $y, $color);
    }
}