PHP 检测 PNG8 或 PNG24

Question

我需要一种简单的方法来检测正在上传的 PNG 文件。我尝试过 getimagesize 但它返回 PNG8 和 PNG24 的第 8 位。任何人都知道如何检测图像是 PNG8，也就是 8 位深度。谢谢！

Answer 1

试试这个来检测 PNG8、PNG24 和 PNG32：

<?php

$file = new SplFileObject('png8.png');

$realPath = $file->getRealPath();

if ($realPath === false) {

    throw new RuntimeException(sprintf('File not found: %s', $file->getFilename()));

}

$file->rewind();

if ($file->fread(4) !== chr(0x89) . 'PNG') {

    // This is not a PNG

    throw new RuntimeException(sprintf('Invalid PNG file: %s', $file->getFilename()));

}

$file->rewind();

$file->fread(8 + 4);

$idr = $file->fread(4);

// Make sure we have an IHDR

if ($idr !== 'IHDR') {

    throw new RuntimeException('No PNG IHDR header found, invalid PNG file.');

}

// PNG actually stores Width and height integers in big-endian.

$width = unpack('N', (string)$file->fread(4))[1];

$height = unpack('N', (string)$file->fread(4))[1];

// Bit depth: 1 byte

// Bit depth is a single-byte integer giving the number of bits per sample or

// per palette index (not per pixel).

//

// Valid values are 1, 2, 4, 8, and 16, although not all values are allowed for all color types.

$bitDepth = ord((string)$file->fread(1));

// Pixel format

// https://en.wikipedia.org/wiki/Portable_Network_Graphics#Pixel_format

// Color type is a single-byte integer that describes the interpretation of the image data.

// Color type codes represent sums of the following values:

// 1 (palette used), 2 (color used), and 4 (alpha channel used).

//

// Valid values are 0, 2, 3, 4, and 6.

$colorType = ord((string)$file->fread(1));

$colorTypes = [

    0 => 'Greyscale',

    2 => 'Truecolour',

    3 => 'Indexed-colour',

    4 => 'Greyscale with alpha',

    6 => 'Truecolour with alpha',

];

$colorTypeText = $colorTypes[$colorType];

$pngType = '?';

// If the bitdepth is 8 and the colortype is 3 (Indexed-colour) you have a PNG8

if ($bitDepth === 8 && $colorType === 3) {

    $pngType = 'PNG8';

}

// If the bitdepth is 8 and colortype is 2 (Truecolour) you have a PNG24.

if ($bitDepth === 8 && $colorType === 2) {

    $pngType = 'PNG24';

}

// If the bitdepth is 8 and colortype is 6 (Truecolour with alpha) you have a PNG32.

if ($bitDepth === 8 && $colorType === 6) {

    $pngType = 'PNG32';

}

echo sprintf('Width: %s, Height: %s, Bit-Depth: %s, Color-Type: %s (%s), Type: %s',

    $width,

    $height,

    $bitDepth,

    $colorType,

    $colorTypeText,

    $pngType

);

输出：

Width: 1500, Height: 500, Bit-Depth: 8, Color-Type: 3 (Indexed-colour), Type: PNG8