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Color Allocation is a very important part when processing image thumbnails. Proper color management allows the thumbnails to retain more details and have better visual effects, avoiding problems such as ribbons and distortion. This article will use PHP as an example to explain some practical color allocation techniques to help you improve the overall quality of thumbnails.
Thumbnails are usually smaller in size and have limited pixel count. If the color allocation is unreasonable, it is easy to cause image quality to decline. For example:
Too small quantities of colors lead to loss of image details.
The color selection is inaccurate, resulting in obvious color difference.
The transparent channel is not properly handled, resulting in background exceptions.
To avoid these problems, we need to reasonably plan and assign colors in the program.
In PHP, GD libraries are commonly used for image processing. The following are several practical techniques:
Prioritize creating a true color canvas before processing the image, ensuring more colors are available.
<?php
// Create a new true color image
$thumbWidth = 200;
$thumbHeight = 200;
$thumb = imagecreatetruecolor($thumbWidth, $thumbHeight);
// Load the original image
$source = imagecreatefromjpeg('https://m66.net/images/original.jpg');
// Copy and resize
imagecopyresampled($thumb, $source, 0, 0, 0, 0, $thumbWidth, $thumbHeight, imagesx($source), imagesy($source));
// Save thumbnails
imagejpeg($thumb, 'https://m66.net/images/thumbnail.jpg');
// Free memory
imagedestroy($thumb);
imagedestroy($source);
?>
imagecreatetruecolor() is the key to avoid the limit of the color quantity and preserve the original image details to the maximum extent.
If your image has a transparent background, such as PNG, be sure to process the transparent information before copying.
<?php
$thumb = imagecreatetruecolor($thumbWidth, $thumbHeight);
$source = imagecreatefrompng('https://m66.net/images/original.png');
// Transparent colors are allowed
imagesavealpha($thumb, true);
$transparent = imagecolorallocatealpha($thumb, 0, 0, 0, 127);
imagefill($thumb, 0, 0, $transparent);
// Copy and resize
imagecopyresampled($thumb, $source, 0, 0, 0, 0, $thumbWidth, $thumbHeight, imagesx($source), imagesy($source));
// Save thumbnails
imagepng($thumb, 'https://m66.net/images/thumbnail.png');
imagedestroy($thumb);
imagedestroy($source);
?>
Imagesavealpha() and imagecolorallocatealpha() can ensure that transparent background remains properly.
During the scaling process, it is recommended to use imagecopyresampled() instead of imagecopyresized() . The former is smoothed and the result is more delicate and natural.
// Correct demonstration
imagecopyresampled($thumb, $source, 0, 0, 0, 0, $thumbWidth, $thumbHeight, imagesx($source), imagesy($source));
Although imagecopyresized() is fast, it is prone to ribbons and is not recommended for high-quality thumbnail generation.
If you finally save it as a GIF, you can use imagetruecolortopalette() to convert the true color image into a palette image and control the number of colors reasonably.
<?php
$thumb = imagecreatetruecolor($thumbWidth, $thumbHeight);
$source = imagecreatefromgif('https://m66.net/images/original.gif');
imagecopyresampled($thumb, $source, 0, 0, 0, 0, $thumbWidth, $thumbHeight, imagesx($source), imagesy($source));
// Convert to color palette，Maximum support256color
imagetruecolortopalette($thumb, true, 256);
// Save thumbnails
imagegif($thumb, 'https://m66.net/images/thumbnail.gif');
imagedestroy($thumb);
imagedestroy($source);
?>
If palette optimization is not done, the GIF will become blurred or the color deviation will be obvious.
In image thumbnail processing, rational allocation of colors, correct management of transparent channels, and use high-quality scaling algorithms can significantly improve the visual and professionalism of the final image.
If you want the thumbnail quality to be a step further, you might as well start with the above tips to optimize your PHP processing process.
Remember: Details determine quality! ??
