Example

function setImagePixelColor($color, int $count)
{
    $width = 400;
    $height = 300;

    $imagick = new \Imagick();
    $imagick->newPseudoImage($width, $height, 'xc:black');
    $imagick->setFormat('jpg');

    for ($i = 0; $i < $count; $i += 1) {
        $imagick->setImagePixelColor(
            mt_rand(0, $width - 1),
            mt_rand(0, $height - 1),
            $color
        );
    }

    header("Content-Type: image/jpeg");
    echo $imagick->getImageBlob();
}