How to adjust the brightness and contrast of an image using PHP

How to use PHP to adjust the brightness and contrast of pictures

Brightness and contrast are one of the important factors in adjusting the visual effect of pictures. In image processing, you can make a picture brighter or darker by adjusting brightness, and you can enhance or weaken the differences between different colors in a picture by adjusting contrast.

As a commonly used server-side scripting language, PHP provides a wealth of image processing functions and libraries. This article will introduce how to use PHP to adjust the brightness and contrast of images, with code examples.

1. Adjust the brightness of the picture

Adjusting the brightness of the picture can be achieved by changing the RGB value of the pixel. Below is an example function that uses the PHP GD library to adjust the brightness of an image.

function adjustBrightness($imagePath, $brightness) {
    $image = imagecreatefromjpeg($imagePath);
    $width = imagesx($image);
    $height = imagesy($image);

    for ($x = 0; $x < $width; $x++) {
        for ($y = 0; $y < $height; $y++) {
            $rgb = imagecolorat($image, $x, $y);
            $oldR = ($rgb >> 16) & 0xFF;
            $oldG = ($rgb >> 8) & 0xFF;
            $oldB = $rgb & 0xFF;

            $newR = $oldR + $brightness;
            $newG = $oldG + $brightness;
            $newB = $oldB + $brightness;

            $newR = max(0, min(255, $newR));
            $newG = max(0, min(255, $newG));
            $newB = max(0, min(255, $newB));

            $newRgb = ($newR << 16) + ($newG << 8) + $newB;

            imagesetpixel($image, $x, $y, $newRgb);
        }
    }

    imagejpeg($image, 'adjusted_image.jpg');
    imagedestroy($image);
}

// 使用示例
adjustBrightness('original_image.jpg', 50); // 将亮度增加50

The above code traverses each pixel of the image, obtains the original RGB value and calculates the new RGB value based on the specified brightness value, and then uses the imagesetpixel function to set the new pixel value. Finally Generate an adjusted image.

2. Adjust the contrast of the picture

Adjusting the contrast of the picture can be achieved by adjusting the range of RGB values ​​of the pixels. Below is an example function that uses the PHP GD library to adjust the contrast of an image.

function adjustContrast($imagePath, $contrast) {
    $image = imagecreatefromjpeg($imagePath);
    $width = imagesx($image);
    $height = imagesy($image);

    for ($x = 0; $x < $width; $x++) {
        for ($y = 0; $y < $height; $y++) {
            $rgb = imagecolorat($image, $x, $y);
            $oldR = ($rgb >> 16) & 0xFF;
            $oldG = ($rgb >> 8) & 0xFF;
            $oldB = $rgb & 0xFF;

            $newR = ($oldR - 127) * $contrast + 127;
            $newG = ($oldG - 127) * $contrast + 127;
            $newB = ($oldB - 127) * $contrast + 127;

            $newR = max(0, min(255, $newR));
            $newG = max(0, min(255, $newG));
            $newB = max(0, min(255, $newB));

            $newRgb = ($newR << 16) + ($newG << 8) + $newB;

            imagesetpixel($image, $x, $y, $newRgb);
        }
    }

    imagejpeg($image, 'adjusted_image.jpg');
    imagedestroy($image);
}

// 使用示例
adjustContrast('original_image.jpg', 1.5); // 将对比度增加1.5倍

The above code traverses each pixel of the image, obtains the original RGB value and calculates a new RGB value based on the specified contrast value, and then uses the imagesetpixel function to set the new pixel value. Finally Generate an adjusted image.

Using PHP to adjust the brightness and contrast of images can provide website developers with more image processing options to achieve better visual effects. Hopefully the code examples in this article will help you achieve this goal.

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