[FIXED] How to convert a "true-color" image to an "one-color" image, with PHP?

Issue

I have read all related questions on Stack Overflow, which has a group-of-word: black-and-white or monochrome. These posts are discussed about one of two common problems: gray-scale or black-and-white.

I do not want my output image in black-color only; but, I want more. I want my output picture in one-color, which is given by a variable, for instance: $MyColor = #336699;, $MyColor = #3366CC; ...

So, my question is not duplicated with any existed question.

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First, I have an original image, which is a true-color image. It is saved in JPEG format:

This original picture has: 16 777 216 colors.

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Then, I could convert it into a gray-scale image, after running this simple script:

<?php 

$source_file = "1.JPG";

$im = ImageCreateFromJpeg($source_file); 

$imgw = imagesx($im);
$imgh = imagesy($im);

for ($i=0; $i<$imgw; $i++)
{
        for ($j=0; $j<$imgh; $j++)
        {

                // Get the RGB value for current pixel

                $rgb = ImageColorAt($im, $i, $j); 

                // Extract each value for: R, G, B

                $rr = ($rgb >> 16) & 0xFF;
                $gg = ($rgb >> 8) & 0xFF;
                $bb = $rgb & 0xFF;

                // Get the value from the RGB value

                $g = round(($rr + $gg + $bb) / 3);

                // Gray-scale values have: R=G=B=G

                $val = imagecolorallocate($im, $g, $g, $g);

                // Set the gray value

                imagesetpixel ($im, $i, $j, $val);
        }
}

header('Content-type: image/jpeg');
imagejpeg($im);

?>

And, below is result:

This gray-scale picture has: 256 colors.

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Now, I want to convert it into a real one-color image:

This one-color picture has: 1 color.

In this case, $MyColor = #000000;.

---

Can you show me: How to convert a true-color image to an one-color image, with PHP?

Solution

Just two lines of code will handle the grey scale conversion and reducing the image to only two colours (because a one-colour image is a blank canvas), with dithering:

$img = imagecreatefromjpeg('./38519049.jpg');

imagefilter($img, IMG_FILTER_GRAYSCALE); // convert to grey scale.
imagetruecolortopalette($img, true, 2); // 'true' for dithering, '2' for number of colours.

header('Content-type: image/jpeg');
imagejpeg($img);

Result:

Answered By - timclutton

Answer Checked By - Willingham (PHPFixing Volunteer)