imagecolorexact() function in PHP

The imagecolorexact() function in PHP retrieves the index of a specified color from an image's color palette. This function is useful when working with palette-based images where you need to find the exact index of a specific RGB color combination.

Syntax

imagecolorexact($img, $red, $green, $blue)

Parameters

• img − Image resource created with functions like imagecreatefrompng() or imagecreatefromjpeg()

• red − Red color component (0-255)

• green − Green color component (0-255)

• blue − Blue color component (0-255)

Return Value

Returns the color index of the specified RGB color in the image palette, or -1 if the exact color does not exist in the palette.

Example

The following example demonstrates finding color indexes in an image ?

<?php
    // Create image resource from PNG file
    $img = imagecreatefrompng('/assets/videos/courses/67/images/course_67_image.png');
    
    $colors = Array();
    
    // Get exact color indexes for specific RGB values
    $colors[] = imagecolorexact($img, 30, 90, 50);
    $colors[] = imagecolorexact($img, 80, 120, 100);
    $colors[] = imagecolorexact($img, 25, 80, 50);
    $colors[] = imagecolorexact($img, 255, 255, 255); // White
    
    print_r($colors);
    
    // Clean up memory
    imagedestroy($img);
?>

The output shows the color indexes found in the image palette ?

Array ( [0] => 1989170 [1] => 5273700 [2] => 1658930 [3] => -1 )

Key Points

• The function only works with palette-based images (GIF, PNG with palette)

• Returns -1 if the exact RGB combination doesn't exist in the palette

• Use imagecolorallocate() to add colors if they don't exist

• RGB values must be between 0 and 255

Conclusion

The imagecolorexact() function is essential for working with palette-based images when you need to find specific color indexes. Use it to verify color existence before performing pixel operations.