Returns the stored color identifier or packed truecolor value at given pixel coordinates.
What It Does
imagecolorallocate() creates a requested RGB color, while matching functions inspect a color table. Coordinates must be inside the image; palette indexes differ from truecolor packed values.
Requirements and Compatibility
GD extension. Sample images and fonts referred to by filename must be supplied locally. Use PHP 8 GdImage objects where applicable; optional decoders depend on the installed build.
Syntax, Inputs and Results
The arguments shown below are concrete values for this function; their types and ranges matter. The example checks return data rather than assuming that every operation succeeds.
Example 1: Basic Use
Call the function with a concrete input and inspect its result.
<?php
if (!extension_loaded('gd')) throw new RuntimeException('GD extension required');
$im = imagecreatetruecolor(160, 110);
$white = imagecolorallocate($im, 255, 255, 255);
imagefilledrectangle($im, 0, 0, 159, 109, $white);
$blue = imagecolorallocate($im, 34, 92, 166);
imagesetpixel($im, 8, 8, $blue);
$result = imagecolorat($im, 8, 8);
var_dump($result);Example 2: Another Case
Change the inputs to observe the behavior on another case.
<?php
if (!extension_loaded('gd')) throw new RuntimeException('GD extension required');
$im = imagecreatetruecolor(160, 110);
$white = imagecolorallocate($im, 255, 255, 255);
imagefilledrectangle($im, 0, 0, 159, 109, $white);
$blue = imagecolorallocate($im, 34, 92, 166);
imagesetpixel($im, 25, 12, $blue);
$result = imagecolorat($im, 25, 12);
var_dump($result);
// This example uses a different target color or alpha state.Practical Example
Use the result to create an output, validate a condition, or complete an image workflow.
<?php
if (!extension_loaded('gd')) throw new RuntimeException('GD extension required');
$im = imagecreatetruecolor(160, 110);
$white = imagecolorallocate($im, 255, 255, 255);
imagefilledrectangle($im, 0, 0, 159, 109, $white);
$pixel = imagecolorat($im, 8, 8);
print_r($pixel);For production, apply the compatibility and edge-case limits described below.
Important Behavior and Edge Cases
Coordinates must be inside the image; palette indexes differ from truecolor packed values.
Comparison with Related Functions and Tools
| Subject | Key difference |
|---|---|
| imagecolorat() | imagecolorallocate() creates a requested RGB color, while matching functions inspect a color table. |
Common Beginner Mistakes
| Mistake | Correct approach |
|---|---|
| Calling imagecolorat() without its required input or supported extension | Check the extension, supply valid arguments, and handle false or exceptions according to the function. |
| Assuming imagecolorat() guarantees a valid or safe image | Coordinates must be inside the image; palette indexes differ from truecolor packed values. |
| Confusing the operation with a related API | imagecolorallocate() creates a requested RGB color, while matching functions inspect a color table. |
Key Takeaways
- Returns the stored color identifier or packed truecolor value at given pixel coordinates.
- Coordinates must be inside the image; palette indexes differ from truecolor packed values.
- Choose the companion API described in the comparison table when the job differs.
Use these examples as a starting point, then validate the result with the actual PHP build, dependencies and inputs used by your application.