按图库中的图像分辨率排序

Question

我不久前做了这个画廊:https://jsfiddle.net/5e9L09Ly/

不要担心它不会上传任何东西.

我说你可以按文件大小排序,但我想按图像分辨率排序.问题是并非所有图像都会加载到页面上,所以我不知道它们的大小.

画廊本身非常基本,它要求一个目录,然后它将显示该目录中的所有图像和视频.

它现在只适用于chrome,只需单击顶部的浏览即可.浏览前的数字是选择目录时应显示或加载的图像数量.

我不知道如何处理这个问题......

我想到的一件事是这样的:

imgLoad.attr("src", url);
imgLoad.unbind("load");
imgLoad.bind("load", function() {
    console.log(url+' size: '+(this.width + this.height));
});

问题是,它会加载它加载的每一个图像,如果你有很多图像,它会给硬盘和浏览器带来很大的压力,比方说你试图加载20k图像.

所以是的......任何建议都会很棒.

我不会在这里发布代码,因为它太多了,请查看小提琴.

Answer 1

理论上，可以通过从上传文件的 arrayBuffer 表示中提取这些值来稍微利用浏览器的处理。

大多数图像格式都有包含媒体尺寸的可读元数据，因此我们可以访问它，而无需要求浏览器实际解析和计算图像数据（解压缩、解码等）。

这是一个非常粗略的概念证明，使用ExifReader lib ，我没有对 jpeg 图像进行太多测试。

/* 
	Rough proof of concept of getting image files width & height
		by reading their metadata directly in arrayBuffer, instead of loading it
	Should support most jpeg png gif and bmp image files
  (though all versions of these formats have NOT been tested)

	@input A fileList.
	@output A promise 
		whose fulfillment handler receives an Array containing successfully parsed files.
*/
function getImageSizes(files) {
  /* Attaches a buffer of the size specified to the File object */
  function getBuffer(fileList, size) {

    return new Promise((resolve, reject) => {

      const fr = new FileReader();
      const toLoad = fileList.length;
      if (!toLoad) { // an empty list
        resolve(fileList);
        return;
      }
      let arr = [];
      let loaded = 0;
      let current = fileList[loaded];
      let chunk = current.slice(0, size || current.size); // get only the required bytes
      fr.onload = e => {
        fileList[loaded].buf = fr.result;

        if (++loaded < toLoad) {
          current = fileList[loaded];
          chunk = current.slice(0, size || current.size);
          fr.readAsArrayBuffer(chunk);
        } else { // once all the list has been treated
          resolve(fileList);
        }
      };

      fr.readAsArrayBuffer(chunk);

    });

  }

  /* png is easy, IHDR starts at 16b, and 8 first bytes are 32bit width & height */
  // You can read https://www.w3.org/TR/PNG-Chunks.html for more info on each numeric value
  function getPNGSizes(pngArray) {
    let view;
    // Little endian only
    function readInt16(offset) {
      return view[offset] << 24 |
        view[offset + 1] << 16 |
        view[offset + 2] << 8 |
        view[offset + 3];
    }

    pngArray.forEach(o => {
      view = new Uint8Array(o.buf);
      o.meta = {
        width: readInt16(16),
        height: readInt16(20),
        bitDepth: view[24],
        colorType: view[25],
        compressionMethod: view[26],
        filterMethod: view[27],
        interlaceMethod: view[28]
      };
      o.width = o.meta.width;
      o.height = o.meta.height;
    });
    return pngArray;
  }

  function getJPEGSizes(jpegArray) {
    /* the EXIF library seems to have some difficulties */
    let failed = [];
    let retry = [];
    let success = [];
    // EXIF data can be anywhere in the file, so we need to get the full arrayBuffer
    return getBuffer(jpegArray).then(jpegArray => {
      jpegArray.forEach(o => {
        try {
          const tags = ExifReader.load(o.buf);
          if (!tags || !tags.PixelXDimension) {
            throw 'no EXIF';
          }
          o.meta = tags; // since OP said he wanted it
          o.width = tags.PixelXDimension.value;
          o.height = tags.PixelYDimension.value;
          success.push(o);
        } catch (e) {
          failed.push(o);
          return;
        }
      });
      // if some have failed, we will retry with the ol'good img way
      retry = failed.map((o) => {
        return new Promise((resolve, reject) => {
          let img = new Image();
          img.onload = e => {
            URL.revokeObjectURL(img.src);
            o.width = img.width;
            o.height = img.height;
            resolve(o);
          };
          img.onerror = e => {
            URL.revokeObjectURL(img.src);
            reject(o);
          };
          img.src = URL.createObjectURL(o);
        });
      });

      return Promise.all(retry)
        // concatenate the no-exif ones with the exif ones.
        .then(arr => success.concat(arr))
    });
  }

  function getGIFSizes(gifArray) {
    gifArray.forEach(o => {
      let view = new Uint8Array(o.buf);
      o.width = view[6] | view[7] << 8;
      o.height = view[8] | view[9] << 8;
    });
    return gifArray;
  }

  function getBMPSizes(bmpArray) {
    let view;

    function readInt(offset) {
      // I probably have something wrong in here...
      return Math.abs(view[offset] |
        view[offset + 1] << 8 |
        view[offset + 2] << 16 |
        view[offset + 3] << 24
      );
    }
    bmpArray.forEach(o => {
      view = new Uint8Array(o.buf);
      o.meta = {
        width: readInt(18),
        height: readInt(22)
      }
      o.width = o.meta.width;
      o.height = o.meta.height;
    });
    return bmpArray;
  }

  // only based on MIME-type string, to avoid all non-images
  function simpleImageFilter(files) {
    return Promise.resolve(
      Array.prototype.filter.call(files, f => f.type.indexOf('image/') === 0)
    );
  }

  function filterType(list, requestedType) {
    // A more robust MIME-type check
    // see http://stackoverflow.com/questions/18299806/how-to-check-file-mime-type-with-javascript-before-upload
    function getHeader(buf) {
      let type = 'unknown';
      let header = Array.prototype.map.call(
        new Uint8Array(buf.slice(0, 4)),
        v => v.toString(16)
      ).join('')

      switch (header) {
        case "89504e47":
        case "0D0A1A0A":
          type = "image/png";
          break;
        case "47494638":
          type = "image/gif";
          break;
        case "ffd8ffe0":
        case "ffd8ffe1":
        case "ffd8ffe2":
          type = "image/jpeg";
          break;
        default:
          switch (header.substr(0, 4)) {
            case "424d":
              type = 'image/bmp';
              break;
          }
          break;
      }
      return type;
    }

    return Array.prototype.filter.call(
      list,
      o => getHeader(o.buf) === requestedType
    );

  }

  function getSizes(fileArray) {
    return getJPEGSizes(filterType(fileArray, 'image/jpeg'))
      .then(jpegs => {
        let pngs = getPNGSizes(filterType(fileArray, 'image/png'));
        let gifs = getGIFSizes(filterType(fileArray, 'image/gif'));
        let bmps = getBMPSizes(filterType(fileArray, 'image/bmp'));
        return gifs.concat(pngs.concat(bmps.concat(jpegs)));
      });
  }

  return simpleImageFilter(files)
    .then(images => getBuffer(images, 30))
    .then(getSizes);
}


// our callback
function sort(arr) {

  arr.sort(function(a, b) {
    return a.width * a.height - b.width * b.height;
  });

  output.innerHTML = '';
  arr.forEach(f => {
    // ugly table generation
    let t = '<td>',
      tt = '</td>' + t,
      ttt = '</td></tr>';
    output.innerHTML += '<tr>' + t + f.name + tt + f.width + tt + f.height + ttt;
  })
}
f.onchange = e => {
  getImageSizes(f.files)
    .then(sort)
    .catch(e => console.log(e));
  output.innerHTML = '<tr><td colspan="3">Processing, please wait...</td></tr>';
}

table {
  margin-top: 12px;
  border-collapse: collapse;
}

td,
th {
  border: 1px solid #000;
  padding: 2px 6px;
}

tr {
  border: 0;
  margin: 0;
}

<script src="https://rawgit.com/mattiasw/ExifReader/master/dist/exif-reader.js"></script>
<input type="file" id="f" webkitdirectory accepts="image/*">
<table>
  <thead>
    <tr>
      <th>file name</th>
      <th>width</th>
      <th>height</th>
    </tr>
  </thead>
  <tbody id="output">
    <tr>
      <td colspan="3">Please choose a folder to upload</td>
    </tr>
  </tbody>
</table>