How to enable or disable interlace using imageinterlace() function in PHP?

The imageinterlace() function is a built-in PHP function used to enable or disable interlacing in images. Interlacing encodes bitmap images so that partially loaded images display as degraded copies of the entire image, allowing users to see portions as the image loads progressively.

Non-interlaced JPEGs appear line-by-line during loading, while interlaced images show a blurred version that becomes clearer. This function controls this behavior by setting the interlace parameter to 1 (enable) or 0 (disable).

Syntax

int imageinterlace(resource $image, int $interlace)

Parameters

The imageinterlace() function accepts two parameters:

• $image − The image resource to be modified

• $interlace − Integer value (1 to enable, 0 to disable interlacing)

Return Value

Returns 1 if the interlace bit is set for the image, otherwise returns 0.

Example 1: Enabling Interlace

This example demonstrates enabling interlacing on a JPEG image −

<?php
    // Create image from file
    $img = imagecreatefromjpeg('/path/to/image.jpg');
    
    // Enable interlacing
    imageinterlace($img, 1);
    
    // Output image with interlacing enabled
    header('Content-type: image/jpeg');
    imagejpeg($img);
    imagedestroy($img);
?>

Example 2: Disabling Interlace

This example shows how to disable interlacing −

<?php
    // Create image from file
    $img = imagecreatefromjpeg('/path/to/image.jpg');
    
    // Disable interlacing
    imageinterlace($img, 0);
    
    // Output image without interlacing
    header('Content-type: image/jpeg');
    imagejpeg($img);
    imagedestroy($img);
?>

Checking Current Interlace Status

You can check if an image has interlacing enabled by calling the function with only the image parameter −

<?php
    // Create a sample image
    $img = imagecreate(100, 100);
    
    // Check current interlace status (default is 0)
    $status = imageinterlace($img);
    echo "Current interlace status: " . $status . "
";
    
    // Enable interlacing
    imageinterlace($img, 1);
    $newStatus = imageinterlace($img);
    echo "New interlace status: " . $newStatus;
    
    imagedestroy($img);
?>

Current interlace status: 0
New interlace status: 1

Conclusion

The imageinterlace() function provides control over image progressive loading behavior. Enable it for web images to improve user experience during slow loading, or disable it for faster processing when progressive display isn't needed.