JavaScript可以检查图像的颜色模式吗？
我对此进行了大量搜索，但我看到的唯一一件事就是颜色模式转换（但是转换希望您设置原始颜色模式）
我添加以下内容：--allow-file-access-from-files以完全控制画布中的img，因为我正在使用GoogleChrome
HTML
<canvas id="canvas" width=6000 height=7919></canvas>
s
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var img = new Image();
img.crossOrigin = "anonymous";
img.onload = start;
img.src = "file:///D:/vincent-van-gogh-the-starry-night-picture-157544-2.png";
最佳答案
是的-基本上JavaScript可以确定png的颜色模式，但因此需要
1.将png转换为base64
2.将base64转换为字节数组
3.读取/解析有关png规范的数组
一种可能的方法如下所示：
var PNG = {
parse: function(imgTag) {
var base64 = PNG.asBase64(imgTag);
var byteData = PNG.utils.base64StringToByteArray(base64);
var parsedPngData = PNG.utils.parseBytes(byteData);
return PNG.utils.enrichParsedData(parsedPngData);
},
asBase64: function(imgTag) {
var canvas = document.createElement("canvas");
canvas.width = imgTag.width;
canvas.height = imgTag.height;
var ctx = canvas.getContext("2d");
ctx.drawImage(imgTag, 0, 0);
var dataURL = canvas.toDataURL("image/png");
return dataURL.split('base64,')[1];
},
utils: {
base64StringToByteArray: function(base64String) {
//http://stackoverflow.com/questions/16245767/creating-a-blob-from-a-base64-string-in-javascript
var byteCharacters = atob(base64String);
var byteNumbers = new Array(byteCharacters.length);
for (var i = 0; i < byteCharacters.length; i++) {
byteNumbers[i] = byteCharacters.charCodeAt(i);
}
return new Uint8Array(byteNumbers);
},
parseBytes: function(bytes) {
var pngData = {};
//see https://en.wikipedia.org/wiki/Portable_Network_Graphics
//verify file header
pngData['headerIsValid'] = bytes[0] == 0x89
&& bytes[1] == 0x50
&& bytes[2] == 0x4E
&& bytes[3] == 0x47
&& bytes[4] == 0x0D
&& bytes[5] == 0x0A
&& bytes[6] == 0x1A
&& bytes[7] == 0x0A
if (!pngData.headerIsValid) {
console.warn('Provided data does not belong to a png');
return pngData;
}
//parsing chunks
var chunks = [];
var chunk = PNG.utils.parseChunk(bytes, 8);
chunks.push(chunk);
while (chunk.name !== 'IEND') {
chunk = PNG.utils.parseChunk(bytes, chunk.end);
chunks.push(chunk);
}
pngData['chunks'] = chunks;
return pngData;
},
parseChunk: function(bytes, start) {
var chunkLength = PNG.utils.bytes2Int(bytes.slice(start, start + 4));
var chunkName = '';
chunkName += String.fromCharCode(bytes[start + 4]);
chunkName += String.fromCharCode(bytes[start + 5]);
chunkName += String.fromCharCode(bytes[start + 6]);
chunkName += String.fromCharCode(bytes[start + 7]);
var chunkData = [];
for (var idx = start + 8; idx<chunkLength + start + 8; idx++) {
chunkData.push(bytes[idx]);
}
//TODO validate crc as required!
return {
start: start,
end: Number(start) + Number(chunkLength) + 12, //12 = 4 (length) + 4 (name) + 4 (crc)
length: chunkLength,
name: chunkName,
data: chunkData,
crc: [
bytes[chunkLength + start + 8],
bytes[chunkLength + start + 9],
bytes[chunkLength + start + 10],
bytes[chunkLength + start + 11]
],
crcChecked: false
};
},
enrichParsedData: function(pngData) {
var idhrChunk = PNG.utils.getChunk(pngData, 'IDHR');
//see http://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html
pngData.width = PNG.utils.bytes2Int(idhrChunk.data.slice(0, 4));
pngData.height = PNG.utils.bytes2Int(idhrChunk.data.slice(4, 8));
pngData.bitDepth = PNG.utils.bytes2Int(idhrChunk.data.slice(8, 9));
pngData.colorType = PNG.utils.bytes2Int(idhrChunk.data.slice(9, 10));
pngData.compressionMethod = PNG.utils.bytes2Int(idhrChunk.data.slice(10, 11));
pngData.filterMethod = PNG.utils.bytes2Int(idhrChunk.data.slice(11, 12));
pngData.interlaceMethod = PNG.utils.bytes2Int(idhrChunk.data.slice(12, 13));
pngData.isGreyScale = pngData.colorType == 0 || pngData.colorType == 4;
pngData.isRgb = pngData.colorType == 2 || pngData.colorType == 6;
pngData.hasAlpha = pngData.colorType == 4 || pngData.colorType == 6;
pngData.hasPaletteMode = pngData.colorType == 3 && PNG.utils.getChunk(pngData, 'PLTE') != null;
return pngData;
},
getChunks: function(pngData, chunkName) {
var chunksForName = [];
for (var idx = 0; idx<pngData.chunks.length; idx++) {
if (pngData.chunks[idx].name = chunkName) {
chunksForName.push(pngData.chunks[idx]);
}
}
return chunksForName;
},
getChunk: function(pngData, chunkName) {
for (var idx = 0; idx<pngData.chunks.length; idx++) {
if (pngData.chunks[idx].name = chunkName) {
return pngData.chunks[idx];
}
}
return null;
},
bytes2Int: function(bytes) {
var ret = 0;
for (var idx = 0; idx<bytes.length; idx++) {
ret += bytes[idx];
if (idx < bytes.length - 1) {
ret = ret << 8;
}
}
return ret;
}
}
}
可以如下使用：
var pngData = PNG.parse(document.getElementById('yourImageId'));
console.log(pngData);
它包含一些信息，例如颜色模式，块数，块本身，位深度等。
希望能帮助到你。