all files / src/imageLoader/ decodeJPEGBaseline8BitColor.js

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import getMinMax from '../shared/getMinMax.js';
 
/**
 * Special decoder for 8 bit jpeg that leverages the browser's built in JPEG decoder for increased performance
 */
 
function arrayBufferToString (buffer) {
  return binaryToString(String.fromCharCode.apply(null, Array.prototype.slice.apply(new Uint8Array(buffer))));
}
 
function binaryToString (binary) {
  let error;
 
  try {
    return decodeURIComponent(escape(binary));
  } catch (_error) {
    error = _error;
    if (error instanceof URIError) {
      return binary;
    }
    throw error;
 
  }
}
 
function decodeJPEGBaseline8BitColor (imageFrame, pixelData, canvas) {
  const start = new Date().getTime();
  const imgBlob = new Blob([pixelData], { type: 'image/jpeg' });
 
  return new Promise((resolve, reject) => {
    const fileReader = new FileReader();
 
    if (fileReader.readAsBinaryString === undefined) {
      fileReader.readAsArrayBuffer(imgBlob);
    } else {
      fileReader.readAsBinaryString(imgBlob); // doesn't work on IE11
    }
 
    fileReader.onload = function () {
      const img = new Image();
 
      img.onload = function () {
        canvas.height = img.height;
        canvas.width = img.width;
        imageFrame.rows = img.height;
        imageFrame.columns = img.width;
        const context = canvas.getContext('2d');
 
        context.drawImage(this, 0, 0);
        const imageData = context.getImageData(0, 0, img.width, img.height);
        const end = new Date().getTime();
 
        imageFrame.pixelData = imageData.data;
        imageFrame.imageData = imageData;
        imageFrame.decodeTimeInMS = end - start;
 
        // calculate smallest and largest PixelValue
        const minMax = getMinMax(imageFrame.pixelData);
 
        imageFrame.smallestPixelValue = minMax.min;
        imageFrame.largestPixelValue = minMax.max;
 
        resolve(imageFrame);
      };
 
      img.onerror = function (error) {
        reject(error);
      };
 
      if (fileReader.readAsBinaryString === undefined) {
        img.src = `data:image/jpeg;base64,${window.btoa(arrayBufferToString(fileReader.result))}`;
      } else {
        img.src = `data:image/jpeg;base64,${window.btoa(fileReader.result)}`; // doesn't work on IE11
      }
    };
 
    fileReader.onerror = (e) => {
      reject(e);
    };
  });
}
 
export default decodeJPEGBaseline8BitColor;