Saves or streams an image as PNG with lossless compression.
What It Does
imagepng() is lossless and supports alpha; JPEG is lossy and has no alpha; AVIF needs codec support. Compression levels range 0–9 and affect size/speed, not visual quality.
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, $white);
if (!imagepng($im, __DIR__ . '/out.png', 6)) throw new RuntimeException('Encoding failed');
echo 'File written';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, $white);
if (!imagepng($im, __DIR__ . '/icon.png', 9)) throw new RuntimeException('Encoding failed');
echo 'File written';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);
ob_start();
$ok = imagepng($im, null, 6);
$bytes = ob_get_clean();
if (!$ok || !is_string($bytes) || $bytes === "") throw new RuntimeException("Image encoder failed");
echo strlen($bytes), " encoded bytes";For production, apply the compatibility and edge-case limits described below.
Important Behavior and Edge Cases
Compression levels range 0–9 and affect size/speed, not visual quality.
Comparison with Related Functions and Tools
| Subject | Key difference |
|---|---|
| imagepng() | imagepng() is lossless and supports alpha; JPEG is lossy and has no alpha; AVIF needs codec support. |
Common Beginner Mistakes
| Mistake | Correct approach |
|---|---|
| Calling imagepng() without its required input or supported extension | Check the extension, supply valid arguments, and handle false or exceptions according to the function. |
| Assuming imagepng() guarantees a valid or safe image | Compression levels range 0–9 and affect size/speed, not visual quality. |
| Confusing the operation with a related API | imagepng() is lossless and supports alpha; JPEG is lossy and has no alpha; AVIF needs codec support. |
Key Takeaways
- Saves or streams an image as PNG with lossless compression.
- Compression levels range 0–9 and affect size/speed, not visual quality.
- 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.