118 lines
2.8 KiB
JavaScript
118 lines
2.8 KiB
JavaScript
'use strict';
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// based on http://www.compix.com/fileformattif.htm
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// TO-DO: support big-endian as well
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var fs = require('fs');
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var readUInt = require('../readUInt');
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function isTIFF (buffer) {
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var hex4 = buffer.toString('hex', 0, 4);
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return ('49492a00' === hex4 || '4d4d002a' === hex4);
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}
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// Read IFD (image-file-directory) into a buffer
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function readIFD (buffer, filepath, isBigEndian) {
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var ifdOffset = readUInt(buffer, 32, 4, isBigEndian);
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// read only till the end of the file
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var bufferSize = 1024;
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var fileSize = fs.statSync(filepath).size;
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if (ifdOffset + bufferSize > fileSize) {
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bufferSize = fileSize - ifdOffset - 10;
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}
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// populate the buffer
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var endBuffer = new Buffer(bufferSize);
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var descriptor = fs.openSync(filepath, 'r');
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fs.readSync(descriptor, endBuffer, 0, bufferSize, ifdOffset);
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// var ifdLength = readUInt(endBuffer, 16, 0, isBigEndian);
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var ifdBuffer = endBuffer.slice(2); //, 2 + 12 * ifdLength);
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return ifdBuffer;
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}
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// TIFF values seem to be messed up on Big-Endian, this helps
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function readValue (buffer, isBigEndian) {
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var low = readUInt(buffer, 16, 8, isBigEndian);
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var high = readUInt(buffer, 16, 10, isBigEndian);
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return (high << 16) + low;
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}
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// move to the next tag
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function nextTag (buffer) {
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if (buffer.length > 24) {
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return buffer.slice(12);
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}
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}
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// Extract IFD tags from TIFF metadata
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function extractTags (buffer, isBigEndian) {
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var tags = {};
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var code, type, length;
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while (buffer && buffer.length) {
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code = readUInt(buffer, 16, 0, isBigEndian);
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type = readUInt(buffer, 16, 2, isBigEndian);
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length = readUInt(buffer, 32, 4, isBigEndian);
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// 0 means end of IFD
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if (code === 0) {
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break;
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} else {
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// 256 is width, 257 is height
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// if (code === 256 || code === 257) {
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if (length === 1 && (type === 3 || type === 4)) {
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tags[code] = readValue(buffer, isBigEndian);
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}
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// move to the next tag
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buffer = nextTag(buffer);
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}
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}
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return tags;
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}
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// Test if the TIFF is Big Endian or Little Endian
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function determineEndianness (buffer) {
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var signature = buffer.toString('ascii', 0, 2);
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if ('II' === signature) {
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return 'LE';
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} else if ('MM' === signature) {
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return 'BE';
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}
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}
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function calculate (buffer, filepath) {
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if (!filepath) {
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throw new TypeError('Tiff doesn\'t support buffer');
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}
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// Determine BE/LE
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var isBigEndian = determineEndianness(buffer) === 'BE';
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// read the IFD
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var ifdBuffer = readIFD(buffer, filepath, isBigEndian);
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// extract the tags from the IFD
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var tags = extractTags(ifdBuffer, isBigEndian);
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var width = tags[256];
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var height = tags[257];
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if (!width || !height) {
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throw new TypeError('Invalid Tiff, missing tags');
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}
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return {
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'width': width,
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'height': height
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};
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}
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module.exports = {
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'detect': isTIFF,
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'calculate': calculate
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};
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