geotiff/dist/predictor.js

GeoTIFF image decoding in JavaScript

'use strict';

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.applyPredictor = applyPredictor;

function decodeRowAcc(row, stride) {
  var length = row.length - stride;
  var offset = 0;
  do {
    for (var i = stride; i > 0; i--) {
      row[offset + stride] += row[offset];
      offset++;
    }

    length -= stride;
  } while (length > 0);
}

function decodeRowFloatingPoint(row, stride, bytesPerSample) {
  var index = 0;
  var count = row.length;
  var wc = count / bytesPerSample;

  while (count > stride) {
    for (var i = stride; i > 0; --i) {
      row[index + stride] += row[index];
      ++index;
    }
    count -= stride;
  }

  var copy = row.slice();
  for (var _i = 0; _i < wc; ++_i) {
    for (var b = 0; b < bytesPerSample; ++b) {
      row[bytesPerSample * _i + b] = copy[(bytesPerSample - b - 1) * wc + _i];
    }
  }
}

function applyPredictor(block, predictor, width, height, bitsPerSample) {
  if (!predictor || predictor === 1) {
    return block;
  }

  for (var i = 0; i < bitsPerSample.length; ++i) {
    if (bitsPerSample[i] % 8 !== 0) {
      throw new Error('When decoding with predictor, only multiple of 8 bits are supported.');
    }
    if (bitsPerSample[i] !== bitsPerSample[0]) {
      throw new Error('When decoding with predictor, all samples must have the same size.');
    }
  }

  var bytesPerSample = bitsPerSample[0] / 8;
  var stride = bitsPerSample.length;

  for (var _i2 = 0; _i2 < height; ++_i2) {
    var row = void 0;
    if (predictor === 2) {
      // horizontal prediction
      switch (bitsPerSample[0]) {
        case 8:
          row = new Uint8Array(block, _i2 * stride * width * bytesPerSample, stride * width * bytesPerSample);
          break;
        case 16:
          row = new Uint16Array(block, _i2 * stride * width * bytesPerSample, stride * width * bytesPerSample / 2);
          break;
        case 32:
          row = new Uint32Array(block, _i2 * stride * width * bytesPerSample, stride * width * bytesPerSample / 4);
          break;
        default:
          throw new Error('Predictor 2 not allowed with ' + bitsPerSample[0] + ' bits per sample.');
      }
      decodeRowAcc(row, stride, bytesPerSample);
    } else if (predictor === 3) {
      // horizontal floating point
      row = new Uint8Array(block, _i2 * stride * width * bytesPerSample, width * bytesPerSample);
      decodeRowFloatingPoint(row, stride, bytesPerSample);
    }
  }
  return block;
}