How to know howmany colors are exist in the image?

Question

<?php
$img=imagecreatefrompng('dense.png');
list($width, $height)=getimagesize('dense.png'); 
$t=0;
for( $i=0 ; $i<$height ; $i++ )
{
    for( $j=0 ; $j<$width ; $j++ )
    {
        $pix  = imagecolorat($img, $i, $j);
        $cols = imagecolorsforindex($img, $pix);
        $r = $cols['red'];
        $g = $cols['green'];
        $b = $cols['blue'];
        $pixel[$i][$j][0]=$r;
        $pixel[$i][$j][1]=$g;
        $pixel[$i][$j][2]=$b;       
        }
}

for( $i=0 ; $i<$height ; $i++ )
{
    for( $j=0 ; $j<$width ; $j++ )
    {
        echo "(".$i.",".$j.") color of that pixel is (".$pixelcolor[$i][$j][0].",".$pixelcolor[$i][$j][1].",".$pixelcolor[$i][$j][2].").</p>";
    }
    echo"<br/>";
}
?>

This is the my code but when i run this code its give me blank webpage.

I want to make one array which store the rgb value of each pixel and it also print on the webpage and reduce those value which are repeating in the array.

so i want to know that how many colors are exist in the images?

A blank page usually means a fatal error. What's in your error log? — georg, Aug 20 '14 at 09:12
When i run my code it gets an error like "TypeError: d.Analytics is undefined". — Yogesh Chalodiya, Aug 20 '14 at 09:51

score 3 · Accepted Answer · answered Aug 22 '14 at 13:22

Your code is probably dying from a memory exhaustion error. Creating a million or so arrays can cause that. Here's a script that counts the number of unique colors in an image in a fairly efficient manner (for PHP):

<?php

$path = "test.jpg";

$img = imagecreatefromjpeg($path);
$w = imagesx($img);
$h = imagesy($img);

// capture the raw data of the image
ob_start();
imagegd2($img, null, $w);
$data = ob_get_clean();
$totalLength = strlen($data);

// calculate the length of the actual pixel data
// from that we can derive the header size
$pixelDataLength = $w * $h * 4;
$headerLength = $totalLength - $pixelDataLength;

// use each four-byte segment as the key to a hash table
$counts = array();
for($i = $headerLength; $i < $totalLength; $i += 4) {
    $pixel = substr($data, $i, 4);
    $count =& $counts[$pixel];
    $count += 1;
}
$colorCount = count($counts);
echo $colorCount;

?>

$colorCount is the number of unique colors in the image. $counts gives you the number of times each color occurs. Each $key is a 4-byte string. The first byte is transparency. A value of zero means opaque. The second, third, and fourth bytes are R, G, and B respectively. You'll need to call ord() to get the value.

score -1 · Answer 2 · answered Aug 20 '14 at 09:29

-1

You can get total number of colors in an image using imagecolorstotal() function

 <?php
    // Create image instance
    $im = imagecreatefromgif('php.gif');

    echo 'Total colors in image: ' . imagecolorstotal($im);

    // Free image
    imagedestroy($im);
 ?>

http://php.net/manual/en/function.imagecolorstotal.php

answered Aug 20 '14 at 09:29

Rakesh Patel

70
6

but when i used this function to find the colors on the png image it give me output as "Total colors in image: 0". – Yogesh Chalodiya Aug 20 '14 at 09:54
1

`imagecolorstotal()` always returns 0 for true-color images. Some people convert true-color images to palette and than count colors but that's far from accurate because you lose a lot of colors during conversion process which is normal when turning 32-bit colors to 24/16/8-bits. In short, function `imagecolorstotal()` is useless in that matter. – Wh1T3h4Ck5 Sep 07 '15 at 13:26

How to know howmany colors are exist in the image?

2 Answers2