diff --git a/src/function.js b/src/function.js index 26b8fe679..3093b0a99 100644 --- a/src/function.js +++ b/src/function.js @@ -125,109 +125,67 @@ var PDFFunction = (function PDFFunctionClosure() { else decode = toMultiArray(decode); - // Precalc the multipliers - var inputMul = new Float64Array(inputSize); - for (var i = 0; i < inputSize; ++i) { - inputMul[i] = (encode[i][1] - encode[i][0]) / - (domain[i][1] - domain[i][0]); - } - - var idxMul = new Int32Array(inputSize); - idxMul[0] = outputSize; - for (i = 1; i < inputSize; ++i) { - idxMul[i] = idxMul[i - 1] * size[i - 1]; - } - - var nSamples = outputSize; - for (i = 0; i < inputSize; ++i) - nSamples *= size[i]; - var samples = this.getSampleArray(size, outputSize, bps, str); return [ CONSTRUCT_SAMPLED, inputSize, domain, encode, decode, samples, size, - outputSize, bps, range, inputMul, idxMul, nSamples + outputSize, Math.pow(2, bps) - 1, range ]; }, constructSampledFromIR: function pdfFunctionConstructSampledFromIR(IR) { - var inputSize = IR[1]; - var domain = IR[2]; - var encode = IR[3]; - var decode = IR[4]; - var samples = IR[5]; - var size = IR[6]; - var outputSize = IR[7]; - var bps = IR[8]; - var range = IR[9]; - var inputMul = IR[10]; - var idxMul = IR[11]; - var nSamples = IR[12]; + // See chapter 3, page 109 of the PDF reference + function interpolate(x, xmin, xmax, ymin, ymax) { + return ymin + ((x - xmin) * ((ymax - ymin) / (xmax - xmin))); + } return function constructSampledFromIRResult(args) { - if (inputSize != args.length) + // See chapter 3, page 110 of the PDF reference. + var m = IR[1]; + var domain = IR[2]; + var encode = IR[3]; + var decode = IR[4]; + var samples = IR[5]; + var size = IR[6]; + var n = IR[7]; + var mask = IR[8]; + var range = IR[9]; + + if (m != args.length) error('Incorrect number of arguments: ' + inputSize + ' != ' + args.length); - // Most of the below is a port of Poppler's implementation. - // TODO: There's a few other ways to do multilinear interpolation such - // as piecewise, which is much faster but an approximation. - var out = new Float64Array(outputSize); - var x; - var e = new Array(inputSize); - var efrac0 = new Float64Array(inputSize); - var efrac1 = new Float64Array(inputSize); - var sBuf = new Float64Array(1 << inputSize); - var i, j, k, idx, t; - // map input values into sample array - for (i = 0; i < inputSize; ++i) { - x = (args[i] - domain[i][0]) * inputMul[i] + encode[i][0]; - if (x < 0) { - x = 0; - } else if (x > size[i] - 1) { - x = size[i] - 1; - } - e[i] = [Math.floor(x), 0]; - if ((e[i][1] = e[i][0] + 1) >= size[i]) { - // this happens if in[i] = domain[i][1] - e[i][1] = e[i][0]; - } - efrac1[i] = x - e[i][0]; - efrac0[i] = 1 - efrac1[i]; - } + var x = args; + var y = new Float64Array(n * m); - // for each output, do m-linear interpolation - for (i = 0; i < outputSize; ++i) { + // Map x_i to y_j for 0 <= i < m using the sampled function. + for (var i = 0; i < m; ++i) { + // x_i' = min(max(x_i, Domain_2i), Domain_2i+1) + var domain_2i = domain[2 * i]; + var domain_2i_1 = domain[2 * i + 1]; + var xi = Math.min(Math.max(x[i], domain_2i), domain_2i_1); - // pull 2^m values out of the sample array - for (j = 0; j < (1 << inputSize); ++j) { - idx = i; - for (k = 0, t = j; k < inputSize; ++k, t >>= 1) { - idx += idxMul[k] * (e[k][t & 1]); - } - if (idx >= 0 && idx < nSamples) { - sBuf[j] = samples[idx]; - } else { - sBuf[j] = 0; // TODO Investigate if this is what Adobe does - } - } + // e_i = Interpolate(x_i', Domain_2i, Domain_2i+1, Encode_2i, Encode_2i+1) + var e = interpolate(xi, domain_2i, domain_2i_1, encode[2 * i], encode[2 * i + 1]); - // do m sets of interpolations - for (j = 0, t = (1 << inputSize); j < inputSize; ++j, t >>= 1) { - for (k = 0; k < t; k += 2) { - sBuf[k >> 1] = efrac0[j] * sBuf[k] + efrac1[j] * sBuf[k + 1]; - } - } + // e_i' = min(max(e_i, 0), Size_i - 1) + e = Math.min(Math.max(e, 0), size[i] - 1); - // map output value to range - out[i] = (sBuf[0] * (decode[i][1] - decode[i][0]) + decode[i][0]); - if (out[i] < range[i][0]) { - out[i] = range[i][0]; - } else if (out[i] > range[i][1]) { - out[i] = range[i][1]; + var in = i * n; + + for (var j = 0; j < n; ++j) { + // average the two nearest neighbors in the sampling table + var rj = (samples[Math.floor(e) * n + j] + samples[Math.ceil(e) * n + j]) / 2; + + // r_j' = Interpolate(r_j, 0, 2^BitsPerSample - 1, Decode_2j, Decode_2j+1) + rj = interpolate(rj, 0, mask, 1, decode[2 * j], decode[2 * j + 1]); + + // y_j = min(max(r_j, range_2j, range_2j+1) + y[in + j] = Math.min(Math.max(rj, range[2 * j], range[2 * j + 1])); } } - return out; + + return y; } },