imagecolorat - PHP code example

The php Function Imagecolorat

The php function imagecolorat allows you to get the color index for a pixel at a specified location in an image. This is an inbuilt function which comes handy when you want to perform operations like changing tints. You can also use this to create a grayscale version of the original image. The function is pretty simple to understand and works the same as any other image manipulation functions in PHP.

You can load image resources from files using the function imagecreatefromfile() or by using the base64_decode() function on a string that represents an image and a file path. You can then perform operations on the image resource like resizing and rotation. You can even apply various filters to the image resource using the imagefilter() function in PHP.

Other useful GD-functions in PHP include the imageflip() function which can be used to flip an image horizontally, vertically or in both directions. You can also use the imageresize() function to resize an image by a specific percentage.

If you are working with a true color image and need to convert it to a grayscale image you can do this using the function imagetogray(image, x, y). You can also use the imagesetpixel(image, x, y, color) function to find out the color value for a specific pixel in an indexed color image.

Another useful function is the imagecopyresampled() function which can be used to create a 1px by 1px copy of an image by sampling the pixels in the image. This is very helpful when you want to do operations that take into account not only the current pixel but its neighbors as well.

imagecolorat example

    private function fixGdImageBlur(array $newSize, $newImage): void
    {
        $colorWhite = (int) imagecolorallocate($newImage, 255, 255, 255);
        $processHeight = $newSize['height'] + 0;
        $processWidth = $newSize['width'] + 0;
        for ($y = 0; $y < $processHeight; ++$y) {
            for ($x = 0; $x < $processWidth; ++$x) {
                $colorat = imagecolorat($newImage, $x, $y);
                $r = ($colorat >> 16) & 0xFF;
                $g = ($colorat >> 8) & 0xFF;
                $b = $colorat & 0xFF;
                if (($r == 253 && $g == 253 && $b == 253) || ($r == 254 && $g == 254 && $b == 254)) {
                    imagesetpixel($newImage, $x, $y, $colorWhite);
                }
            }
        }
    }

    /** * @param resource $newImage * @param int $quality - JPEG quality */

return;
    }
    $distance = pow(($actual[0] - $expected[0]), 2) + pow(($actual[1] - $expected[1]), 2) + pow(($actual[2] - $expected[2]), 2) + pow(($actual[3] - $expected[3]), 2);
    $this->assertLessThanOrEqual($tolerance, $distance, $message . " - Actual: {" . implode(',', $actual) . "}, Expected: {" . implode(',', $expected) . "}, Distance: " . $distance . ", Tolerance: " . $tolerance);
  }

  /** * Function for finding a pixel's RGBa values. */
  public function getPixelColor(ImageInterface $image, int $x, int $y): array {
    $toolkit = $image->getToolkit();
    $color_index = imagecolorat($toolkit->getResource(), $x, $y);

    $transparent_index = imagecolortransparent($toolkit->getResource());
    if ($color_index == $transparent_index) {
      return [0, 0, 0, 127];
    }

    return array_values(imagecolorsforindex($toolkit->getResource(), $color_index));
  }

  /** * Data provider for ::testManipulations(). */