将 PNG Base-64 字符串转换为 TIFF Base-64 字符串

问题描述

我正在使用一个返回 PNG 编码的 base64 字符串的插件，我无法更改它，我必须使用它，但我真正需要的是 tiff 编码值(base-64).有没有办法做到这一点?

I'm using a plugin that returns a PNG encoded base64 string, I cannot change it, I must work with it, but what I really need is the tiff encoded value (base-64). Is there a way of doing this?

我尝试创建一个画布，加载 png base64，然后使用 toDataURL('image/tiff') 但经过一些研究，我发现不支持 tiff 作为 <代码>toDataURL().

I tried to create a canvas, load the png base64 and then used toDataURL('image/tiff') but after some research, I'd found that tiff is not supported as output of toDataURL().

有什么建议吗?

推荐答案

由于浏览器通常不支持 TIFF 作为目标文件格式，因此您必须通过使用 typed 构建文件结构来手动编码 TIFF 文件数组并符合 文件规范(请参阅 Photoshop 笔记 这里).可行:

As TIFF is not generally supported as target file-format in the browser, you will have to manually encode the TIFF file by building up the file-structure using typed arrays and in accordance with the file specifications (see Photoshop notes here). It's doable:

• 从画布中获取原始 RGBA 位图(记住 CORS 很重要)
• 在 DataView 视图中使用类型化数组，以便能够在未对齐的位置写入各种数据
• 构建文件头，定义最小的 TAGS 集并以您需要的方式对 RGBA 数据进行编码(未压缩很容易实现，或者简单的 RLE 压缩).
• 构造最终的文件缓冲区.从这里你有一个 ArrayBuffer 可以作为字节传输，可选:
• 使用 ArrayBuffer 和 tiff mime-type 转换为 Blob.
• 以ArrayBuffer为基础转换为Data-URI

更新 canvas-to-tiff 可用于将画布保存为 TIFF 图像(免责声明:我是作者).

Update canvas-to-tiff can be used to save canvas as TIFF images (disclaimer: I'm the author).

要使用 canvas-to-tiff 获取 Data-URI，您只需执行以下操作:

To get an Data-URI using canvas-to-tiff you can simply do:

CanvasToTIFF.toDataURL(canvasElement, function(url) {
   // url now contains the data-uri.
   window.location = url;    // download, does not work in IE; just to demo
});

虽然，我建议使用 toBlob()，或者如果你想给用户一个链接，toObjectURL()(而不是 toDataURL).

Although, I would recommend using toBlob(), or if you want to give the user a link, toObjectURL() (instead of toDataURL).

var c = document.querySelector("canvas"),
    ctx = c.getContext("2d");

// draw some graphics
ctx.strokeStyle = "rgb(0, 135, 222)";
ctx.lineWidth = 30;
ctx.arc(200, 200, 170, 0, 2*Math.PI);
ctx.stroke();

// Covert to TIFF using Data-URI (slower, larger size)
CanvasToTIFF.toDataURL(c, function(url) {
  var a = document.querySelector("a");
  a.href = url;
  a.innerHTML = "Right-click this link, select Save As to save the TIFF";
})

<script src="https://cdn.rawgit.com/epistemex/canvas-to-tiff/master/canvastotiff.min.js">
</script>
<a href=""></a><br>
<canvas width=400 height=400></canvas>

var c = document.querySelector("canvas"),
    ctx = c.getContext("2d");

// draw some graphics
ctx.strokeStyle = "rgb(0, 135, 222)";
ctx.lineWidth = 30;
ctx.arc(200, 200, 170, 0, 2*Math.PI);
ctx.stroke();

// Covert to TIFF using Object-URL (faster, smaller size)
CanvasToTIFF.toObjectURL(c, function(url) {
  var a = document.querySelector("a");
  a.href = url;
  a.innerHTML = "Right-click this link, select Save As to save the TIFF";
})

<script src="https://cdn.rawgit.com/epistemex/canvas-to-tiff/master/canvastotiff.min.js">
</script>
<a href=""></a><br>
<canvas width=400 height=400></canvas>

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