How to convert binary to image in php

With the continuous advancement of information technology and the rise of Web2.0, people's demand for multimedia information is getting higher and higher. Picture formats such as PNG, JPG, and GIF have become an indispensable part of our lives. As PHP code is the most widely used language in web development, how to convert binary to images has become one of the basic skills that programmers need to master.

1. Conversion between binary and hexadecimal

Before learning how to convert binary into pictures, we need to master the mutual conversion between binary and hexadecimal. Taking 8 binary bits as a group, that is, one byte as a unit, it can represent an integer between 0 and 255; and every four binary bits correspond to a hexadecimal number, that is, one byte uses two hexadecimal digits. Number representation. For example, the binary number 11001000 corresponds to the hexadecimal number 0xC8, and the hexadecimal number 0x50 corresponds to the binary number 01010000.

We can use PHP's sprintf function to convert an integer in any base into a base string with a specified number of digits. For example, to convert the integer represented by $int into an 8-digit binary string, you can use the following code:

$bin = sprintf("%08b", $int);

Similarly, to convert the integer represented by $int into a 2-digit hexadecimal string For strings, you can use the following code:

$hex = sprintf("%02x", $int);

2. Convert binary to image

Next, we will learn how to convert binary string to PNG image. The PNG image format supports multiple colors of transparency without compression loss, so it is widely used in web development.

First, we need to define a $binary variable to save the byte array converted from the binary string. For a 24-bit true color (RGB) PNG image, its pixel value consists of 3 bytes of RGB values. Therefore, during the conversion process, the binary string needs to be cut into groups of 3 bytes. point. After the segmentation is completed, each group of bytes can be used as the value of the three RGB channels to generate the pixel array of the PNG image. After generating the pixel array, use the imagepng function to write the pixel array into a PNG image file to generate a PNG image.

The complete code is as follows:

//将二进制字符串转为PNG图片
function binaryToPNG($binary, $width, $height) {
    //计算像素数组的长度（每个像素由3个字节的RGB值组成）
    $len = strlen($binary);
    $pixelLen = $len / 3;
    //通过imagecreatetruecolor函数创建一个PNG图片的像素数组
    $im = imagecreatetruecolor($width, $height);
    //遍历二进制字符串，将每一组3个字节的值分别作为RGB三通道的值，并生成像素数组
    for ($i = 0; $i < $pixelLen; $i++) {
        $r = ord($binary[$i * 3]);
        $g = ord($binary[$i * 3 + 1]);
        $b = ord($binary[$i * 3 + 2]);
        imagesetpixel($im, $i % $width, floor($i / $width), imagecolorallocate($im, $r, $g, $b));
    }
    //使用imagepng函数将像素数组写入PNG图片文件中，从而生成PNG图片
    header('Content-Type:image/png');
    imagepng($im);
    imagedestroy($im);
}

Finally, we need to convert the binary string into a PHP byte array before we can operate it in the binaryToPNG function. For a binary string in the shape of "0100101010101001010...", you can use the following code to convert it into a PHP byte array:

$binary = pack("B*", $binaryString);

3. Convert the image to binary

Corresponding to converting binary to pictures, we also need to convert pictures into binary strings. In this process, you can use the imagecreatefrompng function to read the PNG image as a pixel array, then use the imagecolorat function to obtain the RGB value of each pixel, and finally splice the RGB values ​​into a binary string. The complete code is as follows:

//将PNG图片转为二进制字符串
function pngToBinary($file) {
    //通过imagecreatefrompng函数将PNG图片读取为像素数组
    $im = imagecreatefrompng($file);
    $width = imagesx($im);
    $height = imagesy($im);
    $binary = '';
    //遍历像素数组，获取每个像素的RGB值，拼接成一组二进制字符串
    for ($y = 0; $y < $height; $y++) {
        for ($x = 0; $x < $width; $x++) {
            $rgb = imagecolorat($im, $x, $y);
            $r = ($rgb >> 16) & 0xFF;
            $g = ($rgb >> 8) & 0xFF;
            $b = $rgb & 0xFF;
            $binary .= sprintf("%02x%02x%02x", $r, $g, $b);
        }
    }
    return $binary;
}

4. Summary

This article details how to convert a binary string into a PNG image, and how to convert a PNG image into a binary string. Through learning, we can not only master the mutual conversion method between binary and hexadecimal in PHP, but also how to perform image operations in PHP code. In actual development, these basic skills can help us better complete multimedia-related operations and provide strong support for Web development.

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