js-dicom/src/ImageUtility/decodeJPEGBaseline8BitColor.js

this is js-dicom

import $ from 'jquery';

/**
 * 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 deferred = $.Deferred();

    const imgBlob = new Blob([pixelData], { type: 'image/jpeg' });

    const r = new FileReader();

    if (r.readAsBinaryString === undefined) {
        r.readAsArrayBuffer(imgBlob);
    } else {
        r.readAsBinaryString(imgBlob); // doesn't work on IE11
    }

    r.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);


            imageFrame.pixelData = imageData.data;
            imageFrame.imageData = imageData;
            deferred.resolve(imageFrame);
        };
        img.onerror = function (error) {
            deferred.reject(error);
        };
        if (r.readAsBinaryString === undefined) {
            img.src = `data:image/jpeg;base64,${window.btoa(arrayBufferToString(r.result))}`;
        } else {
            img.src = `data:image/jpeg;base64,${window.btoa(r.result)}`; // doesn't work on IE11
        }

    };

    return deferred.promise();
}

export default decodeJPEGBaseline8BitColor;