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Detailed explanation of imageflip() and imagecreatefromjpeg()

M66 2025-05-18

During PHP image processing, we often need to rotate, scale, flip the image and other operations. The imageflip() function is a practical function for image flipping introduced in PHP 5.5.0. It can read JPEG images with imagecreatefromjpeg() , and easily achieve horizontal or vertical flipping and other effects. This article will explain in detail how to use these two functions to quickly realize image flip processing.

1. Introduction to imagecreatefromjpeg()

imagecreatefromjpeg() is a GD library function that creates image resources from JPEG files. Its basic syntax is as follows:

 resource imagecreatefromjpeg(string $filename)

This function returns an image resource that can be used for subsequent image processing operations.

Example:

 $img = imagecreatefromjpeg('https://m66.net/images/sample.jpg');

This code reads the JPEG image from the specified URL and converts it to the image resource $img .

2. Introduction to imageflip()

The imageflip() function is used to flip an image and supports three methods: horizontal flip, vertical flip and bidirectional flip. The syntax is as follows:

 bool imageflip(GdImage $image, int $mode)

  • $image : The image resource to be flipped

  • $mode : flip method, optional values ​​include:

    • IMG_FLIP_HORIZONTAL : Horizontal flip

    • IMG_FLIP_VERTICAL : vertical flip

    • IMG_FLIP_BOTH : Flip horizontally and vertically simultaneously

3. Sample code: Implement picture flip

Here is a complete PHP code example showing how to load a JPEG image from a remote image address and flip it horizontally:

 <?php
// Set up pictures URL（The example domain name is m66.net）
$imageUrl = 'https://m66.net/images/sample.jpg';

// Create image resources
$image = imagecreatefromjpeg($imageUrl);

// Check if the image is created successfully
if (!$image) {
    die('无法Create image resources，Please check if the image path is correct。');
}

// Perform horizontal flip
imageflip($image, IMG_FLIP_HORIZONTAL);

// Set the response header to image type
header('Content-Type: image/jpeg');

// Output the flipped image
imagejpeg($image);

// Destroy image resources
imagedestroy($image);
?>

After running the script in your browser, you will see the result of the original image being flipped horizontally.

4. More application scenarios

Through the combination of the above functions, we can implement various image processing scenarios, such as:

  • Automatic horizontal flip of user avatar

  • Implement image mirroring effect

  • Dynamic preview processing after front-end image upload

  • Image effects production (such as reflection)

V. Conclusion

imagecreatefromjpeg() and imageflip() are powerful combinations in PHP image processing, which can help us quickly achieve image flip effect. This operation is very practical especially in dynamic websites or image editing functions. If you want to further explore image processing, it is recommended to gain insight into more features of the PHP GD library, such as rotation ( imagerotate() ), scaling ( imagescale() ), cropping ( imagecrop() ), etc.

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