如何从base64字符串的图像数据中同步获取宽度和高度?

时间:2016-12-14 19:16:02

标签: javascript arrays actionscript-3 flash bitmapdata

有没有办法从base64编码的图像数据中获取图像宽度和高度同步?可能是标题信息。

我必须非常清楚。我对异步方法不感兴趣。如果您想知道async不起作用的原因,请继续。甚至不评论。

这是我编码数据的示例代码。编码是同步的。我正在使用此call

var base64ImageData:String = DisplayObjectUtils.getBase64ImageDataString(displayObject, DisplayObjectUtils.PNG, null, true);

这是我解码数据的代码。我在AS3中发现的唯一解码方法是异步的。我正在使用此call

var bitmapData:BitmapData = DisplayObjectUtils.getBitmapDataFromBase64(bitmapDataString);

让我再说一遍,我正在寻找一个同步动作。它不能是异步的。

更多信息:
我正在使用ActionScript3,它是JavaScript的兄弟。如果它在JavaScript中工作,它很可能在AS3中工作。但我无法使用dom。不向dom添加图像和检查值。

有用的黑客:
如果可以在base64流中添加宽度和高度,然后稍后再获取它也可以。

3 个答案:

答案 0 :(得分:3)

这仅适用于png 首先要做的是转换base64做一个缓冲区(Uint8array)然后读取字节16-20(宽度)和20-24(高度)作为int32值



function getPngDimensions(base64) {
  let header = base64.slice(0, 50)
  let uint8 = Uint8Array.from(atob(header), c => c.charCodeAt(0))
  let dataView = new DataView(uint8.buffer, 0, 28)

  return {
    width: dataView.getInt32(16),
    height: dataView.getInt32(20)
  }
}

// Just to get some random base64 images
var random = (bottom, top) => Math.floor( Math.random() * ( 1 + top - bottom ) ) + bottom
var canvas = document.createElement('canvas')
canvas.width = random(10, 100)
canvas.height = random(10, 100)
console.log(`canvas width: ${canvas.width}, height: ${canvas.height}`)
var base64 = canvas.toDataURL().split(',')[1]
console.log(base64)

var dimensions = getPngDimensions(base64)
console.log(dimensions)




答案 1 :(得分:2)

以下不起作用,但它试图将@Endless答案转换为AS3。到目前为止我有这个:

protected function windowedapplication1_applicationCompleteHandler(event:FlexEvent):void {
    var base64ImageData:String = DisplayObjectUtils.getBase64ImageDataString(this, DisplayObjectUtils.PNG, null, true);
    var size:Object = getPngDimensions(base64ImageData);
}

public function getPngDimensions(base64:String):Point {
    base64 = base64.split(',')[1];
    trace(base64.length);
    base64 = base64.replace(/\n/g, "");
    trace(base64.length);
    //var header:String = base64.slice(0, 52); // 50 gave error later on
    var header:String = base64.slice(0, base64.length);
    var base64Decoder:Base64Decoder = new Base64Decoder();
    var byteArray:ByteArray;

    base64Decoder.reset();
    base64Decoder.decode(header);

    // base64Decoder.toByteArray(); ==>
    // Error: A partial block (2 of 4 bytes) was dropped. Decoded data is probably truncated!
    // added the whole length (52 works as well)
    byteArray = base64Decoder.toByteArray();
    byteArray.position = 0;

    //var width:String = byteArray.readUTFBytes(0);
    //var value:ByteArray = new ByteArray();
    //value.readBytes(byteArray, 0, 28);
    var thing:Number = byteArray.readDouble(); // -8.091055181950927E-264
    byteArray.position = 0;
    var thing2:Number = byteArray.readFloat(); // -2.5073895107184266E-33
    byteArray.position = 0;
    var width:Number = byteArray.readFloat();
    byteArray.position = 16;
    var width:Number = byteArray.readFloat();
    byteArray.position = 20;
    var width:Number = byteArray.readFloat();
    byteArray.position = 28;
    var width:Number = byteArray.readFloat(); // 1.1074230549312416E-38
    byteArray.position = 0;
    var other:String = byteArray.readUTFBytes(byteArray.length);
    // other == "PNG\r\n\n"

    var point:Point = new Point();
    point.x = int(width);
    point.y = int(height);

    return point;
}

如果我使用ByteArray.readUTFBytes()我会得到" PNG"结果但没有宽度或高度。

答案 2 :(得分:1)

  

“如果我使用ByteArray.readUTFBytes()我会得到”PNG“,但没有宽度或高度。”

不要将字节读取为UTF格式,因为它只提取文本字符。你想要小数值。

  • readDoublereadFloat太多,每次操作读取8个字节。 PNG格式每个宽度或高度值仅使用4个字节,因此只读取(无符号)整数。
  • 请记住,每个read操作都会自动移动byteArray位置。例如,要知道bytePos-1的值,你必须“走”/读过它,所以你最终得到bytePos-2,或者对于Double类型,你最终会得到bytePos-9。

查看代码的重新修复是否获得了宽度和宽度的预期值。身高......

public function getPngDimensions(base64:String):Point 
{
    base64 = base64.split(',')[1];
    trace("Base64 length A : " + base64.length);
    base64 = base64.replace(/\n/g, "");
    trace("Base64 length B : " + base64.length);
    //var header:String = base64.slice(0, 52); // 50 gave error later on
    var header:String = base64.slice(0, base64.length);
    var base64Decoder:Base64Decoder = new Base64Decoder();
    var byteArray:ByteArray;

    base64Decoder.reset();
    base64Decoder.decode(header);

    // base64Decoder.toByteArray(); ==>
    // Error: A partial block (2 of 4 bytes) was dropped. Decoded data is probably truncated!
    // added the whole length (52 works as well)
    byteArray = base64Decoder.toByteArray();
    byteArray.position = 0;

    //# Get Width and Height values
    //# type Int is 4 bytes long so pointer auto-moves ahead by 4 bytes during Read action
    byteArray.position = 16; //start position for values...
    var width:int = byteArray.readUnsignedInt(); //reads 4 bytes, stops at Pos 20
    var height:int = byteArray.readUnsignedInt(); //reads 4 bytes, stops at Pos 24

    //# Double check (if needed)
    //trace("PNG width  : " + width);
    //trace("PNG height : " + height);

    //# Return as Point
    var point:Point = new Point();
    point.x = width; point.y = height;
    return point;
}