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+/**
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+ * var dataUrl = canvas.toDataURL('image/jpeg', 0.92);
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+ * var daurl150dpi = changeDpiDataUrl(dataUrl, 150);
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+ *
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+ * canvas.toBlob(function(blob) {
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+ * changeDpiBlob(blob, 300).then(function(blob){
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+ * // use your changed blob
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+ * })
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+ * },'image/jpeg', 0.92);
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+ *
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+ */
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+
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+
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+let pngDataTable: any;
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+
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+const PNG = 'image/png';
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+const JPEG = 'image/jpeg';
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+function createPngDataTable() {
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+ /* Table of CRCs of all 8-bit messages. */
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+ const crcTable = new Int32Array(256);
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+ for (let n = 0; n < 256; n++) {
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+ let c = n;
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+ for (let k = 0; k < 8; k++) {
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+ c = (c & 1) ? 0xedb88320 ^ (c >>> 1) : c >>> 1;
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+ }
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+ crcTable[n] = c;
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+ }
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+ return crcTable;
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+}
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+
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+function calcCrc(buf: any) {
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+ let c = -1;
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+ if (!pngDataTable) pngDataTable = createPngDataTable();
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+ for (let n = 0; n < buf.length; n++) {
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+ c = pngDataTable[(c ^ buf[n]) & 0xFF] ^ (c >>> 8);
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+ }
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+ return c ^ -1;
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+}
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+
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+function searchStartOfPhys(data: any[]) {
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+ const length = data.length - 1;
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+ // we check from the end since we cut the string in proximity of the header
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+ // the header is within 21 bytes from the end.
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+ for (let i = length; i >= 4; i--) {
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+ if (data[i - 4] === 9 && data[i - 3] === _P &&
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+ data[i - 2] === _H && data[i - 1] === _Y &&
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+ data[i] === _S) {
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+ return i - 3;
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+ }
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+ }
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+}
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+
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+function changeDpiOnArray(dataArray: any, dpi: any, format: any, overwritepHYs?: any) {
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+ if (format === JPEG) {
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+ dataArray[13] = 1; // 1 pixel per inch or 2 pixel per cm
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+ dataArray[14] = dpi >> 8; // dpiX high byte
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+ dataArray[15] = dpi & 0xff; // dpiX low byte
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+ dataArray[16] = dpi >> 8; // dpiY high byte
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+ dataArray[17] = dpi & 0xff; // dpiY low byte
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+ return dataArray;
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+ }
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+ if (format === PNG) {
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+ const physChunk = new Uint8Array(13);
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+ // chunk header pHYs
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+ // 9 bytes of data
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+ // 4 bytes of crc
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+ // this multiplication is because the standard is dpi per meter.
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+ dpi *= 39.3701;
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+ physChunk[0] = _P;
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+ physChunk[1] = _H;
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+ physChunk[2] = _Y;
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+ physChunk[3] = _S;
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+ physChunk[4] = dpi >>> 24; // dpiX highest byte
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+ physChunk[5] = dpi >>> 16; // dpiX veryhigh byte
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+ physChunk[6] = dpi >>> 8; // dpiX high byte
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+ physChunk[7] = dpi & 0xff; // dpiX low byte
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+ physChunk[8] = physChunk[4]; // dpiY highest byte
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+ physChunk[9] = physChunk[5]; // dpiY veryhigh byte
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+ physChunk[10] = physChunk[6]; // dpiY high byte
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+ physChunk[11] = physChunk[7]; // dpiY low byte
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+ physChunk[12] = 1; // dot per meter....
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+
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+ const crc = calcCrc(physChunk);
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+
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+ const crcChunk = new Uint8Array(4);
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+ crcChunk[0] = crc >>> 24;
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+ crcChunk[1] = crc >>> 16;
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+ crcChunk[2] = crc >>> 8;
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+ crcChunk[3] = crc & 0xff;
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+
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+ if (overwritepHYs) {
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+ const startingIndex: any = searchStartOfPhys(dataArray);
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+ dataArray.set(physChunk, startingIndex);
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+ dataArray.set(crcChunk, startingIndex + 13);
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+ return dataArray;
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+ } else {
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+ // i need to give back an array of data that is divisible by 3 so that
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+ // dataurl encoding gives me integers, for luck this chunk is 17 + 4 = 21
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+ // if it was we could add a text chunk contaning some info, untill desired
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+ // length is met.
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+
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+ // chunk structur 4 bytes for length is 9
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+ const chunkLength = new Uint8Array(4);
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+ chunkLength[0] = 0;
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+ chunkLength[1] = 0;
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+ chunkLength[2] = 0;
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+ chunkLength[3] = 9;
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+
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+ const finalHeader = new Uint8Array(54);
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+ finalHeader.set(dataArray, 0);
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+ finalHeader.set(chunkLength, 33);
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+ finalHeader.set(physChunk, 37);
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+ finalHeader.set(crcChunk, 50);
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+ return finalHeader;
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+ }
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+ }
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+}
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+
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+// those are 3 possible signature of the physBlock in base64.
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+// the pHYs signature block is preceed by the 4 bytes of lenght. The length of
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+// the block is always 9 bytes. So a phys block has always this signature:
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+// 0 0 0 9 p H Y s.
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+// However the data64 encoding aligns we will always find one of those 3 strings.
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+// this allow us to find this particular occurence of the pHYs block without
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+// converting from b64 back to string
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+const b64PhysSignature1 = 'AAlwSFlz';
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+const b64PhysSignature2 = 'AAAJcEhZ';
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+const b64PhysSignature3 = 'AAAACXBI';
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+
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+const _P = 'p'.charCodeAt(0);
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+const _H = 'H'.charCodeAt(0);
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+const _Y = 'Y'.charCodeAt(0);
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+const _S = 's'.charCodeAt(0);
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+
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+export function changeDpiBlob(blob: any, dpi: any) {
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+ // 33 bytes are ok for pngs and jpegs
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+ // to contain the information.
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+ const headerChunk = blob.slice(0, 33);
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+ return new Promise((resolve, reject) => {
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+ const fileReader: any = new FileReader();
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+ fileReader.onload = () => {
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+ const dataArray = new Uint8Array(fileReader.result);
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+ const tail = blob.slice(33);
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+ const changedArray = changeDpiOnArray(dataArray, dpi, blob.type);
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+ resolve(new Blob([changedArray, tail], { type: blob.type }));
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+ };
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+ fileReader.readAsArrayBuffer(headerChunk);
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+ });
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+}
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+
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+export function changeDpiDataUrl(base64Image: any, dpi: any) {
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+ const dataSplitted = base64Image.split(',');
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+ const format = dataSplitted[0];
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+ const body = dataSplitted[1];
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+ let type;
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+ let headerLength;
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+ let overwritepHYs = false;
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+ if (format.indexOf(PNG) !== -1) {
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+ type = PNG;
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+ const b64Index = detectPhysChunkFromDataUrl(body);
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+ // 28 bytes in dataUrl are 21bytes, length of phys chunk with everything inside.
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+ if (b64Index >= 0) {
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+ headerLength = Math.ceil((b64Index + 28) / 3) * 4;
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+ overwritepHYs = true;
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+ } else {
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+ headerLength = 33 / 3 * 4;
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+ }
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+ }
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+ if (format.indexOf(JPEG) !== -1) {
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+ type = JPEG;
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+ headerLength = 18 / 3 * 4;
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+ }
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+ // 33 bytes are ok for pngs and jpegs
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+ // to contain the information.
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+ const stringHeader = body.substring(0, headerLength);
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+ const restOfData = body.substring(headerLength);
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+ const headerBytes = atob(stringHeader);
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+ const dataArray = new Uint8Array(headerBytes.length);
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+ for (let i = 0; i < dataArray.length; i++) {
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+ dataArray[i] = headerBytes.charCodeAt(i);
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+ }
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+ const finalArray = changeDpiOnArray(dataArray, dpi, type, overwritepHYs);
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+ const base64Header = btoa(String.fromCharCode(...finalArray));
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+ return [format, ',', base64Header, restOfData].join('');
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+}
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+
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+function detectPhysChunkFromDataUrl(data: any) {
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+ let b64index = data.indexOf(b64PhysSignature1);
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+ if (b64index === -1) {
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+ b64index = data.indexOf(b64PhysSignature2);
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+ }
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+ if (b64index === -1) {
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+ b64index = data.indexOf(b64PhysSignature3);
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+ }
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+ // if b64index === -1 chunk is not found
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+ return b64index;
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+}
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