implement sampled functions based on the PDF spec
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Andreas Gal
parent
9650df5c10
commit
59283bdf6d
126
src/function.js
126
src/function.js
@ -125,109 +125,67 @@ var PDFFunction = (function PDFFunctionClosure() {
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else
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decode = toMultiArray(decode);
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// Precalc the multipliers
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var inputMul = new Float64Array(inputSize);
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for (var i = 0; i < inputSize; ++i) {
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inputMul[i] = (encode[i][1] - encode[i][0]) /
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(domain[i][1] - domain[i][0]);
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}
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var idxMul = new Int32Array(inputSize);
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idxMul[0] = outputSize;
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for (i = 1; i < inputSize; ++i) {
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idxMul[i] = idxMul[i - 1] * size[i - 1];
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}
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var nSamples = outputSize;
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for (i = 0; i < inputSize; ++i)
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nSamples *= size[i];
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var samples = this.getSampleArray(size, outputSize, bps, str);
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return [
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CONSTRUCT_SAMPLED, inputSize, domain, encode, decode, samples, size,
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outputSize, bps, range, inputMul, idxMul, nSamples
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outputSize, Math.pow(2, bps) - 1, range
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];
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},
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constructSampledFromIR: function pdfFunctionConstructSampledFromIR(IR) {
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var inputSize = IR[1];
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var domain = IR[2];
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var encode = IR[3];
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var decode = IR[4];
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var samples = IR[5];
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var size = IR[6];
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var outputSize = IR[7];
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var bps = IR[8];
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var range = IR[9];
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var inputMul = IR[10];
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var idxMul = IR[11];
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var nSamples = IR[12];
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// See chapter 3, page 109 of the PDF reference
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function interpolate(x, xmin, xmax, ymin, ymax) {
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return ymin + ((x - xmin) * ((ymax - ymin) / (xmax - xmin)));
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}
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return function constructSampledFromIRResult(args) {
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if (inputSize != args.length)
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// See chapter 3, page 110 of the PDF reference.
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var m = IR[1];
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var domain = IR[2];
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var encode = IR[3];
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var decode = IR[4];
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var samples = IR[5];
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var size = IR[6];
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var n = IR[7];
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var mask = IR[8];
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var range = IR[9];
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if (m != args.length)
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error('Incorrect number of arguments: ' + inputSize + ' != ' +
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args.length);
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// Most of the below is a port of Poppler's implementation.
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// TODO: There's a few other ways to do multilinear interpolation such
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// as piecewise, which is much faster but an approximation.
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var out = new Float64Array(outputSize);
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var x;
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var e = new Array(inputSize);
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var efrac0 = new Float64Array(inputSize);
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var efrac1 = new Float64Array(inputSize);
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var sBuf = new Float64Array(1 << inputSize);
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var i, j, k, idx, t;
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// map input values into sample array
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for (i = 0; i < inputSize; ++i) {
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x = (args[i] - domain[i][0]) * inputMul[i] + encode[i][0];
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if (x < 0) {
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x = 0;
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} else if (x > size[i] - 1) {
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x = size[i] - 1;
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}
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e[i] = [Math.floor(x), 0];
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if ((e[i][1] = e[i][0] + 1) >= size[i]) {
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// this happens if in[i] = domain[i][1]
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e[i][1] = e[i][0];
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}
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efrac1[i] = x - e[i][0];
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efrac0[i] = 1 - efrac1[i];
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}
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var x = args;
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var y = new Float64Array(n * m);
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// for each output, do m-linear interpolation
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for (i = 0; i < outputSize; ++i) {
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// Map x_i to y_j for 0 <= i < m using the sampled function.
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for (var i = 0; i < m; ++i) {
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// x_i' = min(max(x_i, Domain_2i), Domain_2i+1)
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var domain_2i = domain[2 * i];
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var domain_2i_1 = domain[2 * i + 1];
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var xi = Math.min(Math.max(x[i], domain_2i), domain_2i_1);
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// pull 2^m values out of the sample array
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for (j = 0; j < (1 << inputSize); ++j) {
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idx = i;
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for (k = 0, t = j; k < inputSize; ++k, t >>= 1) {
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idx += idxMul[k] * (e[k][t & 1]);
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}
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if (idx >= 0 && idx < nSamples) {
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sBuf[j] = samples[idx];
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} else {
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sBuf[j] = 0; // TODO Investigate if this is what Adobe does
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}
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}
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// e_i = Interpolate(x_i', Domain_2i, Domain_2i+1, Encode_2i, Encode_2i+1)
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var e = interpolate(xi, domain_2i, domain_2i_1, encode[2 * i], encode[2 * i + 1]);
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// do m sets of interpolations
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for (j = 0, t = (1 << inputSize); j < inputSize; ++j, t >>= 1) {
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for (k = 0; k < t; k += 2) {
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sBuf[k >> 1] = efrac0[j] * sBuf[k] + efrac1[j] * sBuf[k + 1];
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}
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}
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// e_i' = min(max(e_i, 0), Size_i - 1)
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e = Math.min(Math.max(e, 0), size[i] - 1);
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// map output value to range
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out[i] = (sBuf[0] * (decode[i][1] - decode[i][0]) + decode[i][0]);
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if (out[i] < range[i][0]) {
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out[i] = range[i][0];
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} else if (out[i] > range[i][1]) {
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out[i] = range[i][1];
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var in = i * n;
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for (var j = 0; j < n; ++j) {
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// average the two nearest neighbors in the sampling table
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var rj = (samples[Math.floor(e) * n + j] + samples[Math.ceil(e) * n + j]) / 2;
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// r_j' = Interpolate(r_j, 0, 2^BitsPerSample - 1, Decode_2j, Decode_2j+1)
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rj = interpolate(rj, 0, mask, 1, decode[2 * j], decode[2 * j + 1]);
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// y_j = min(max(r_j, range_2j, range_2j+1)
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y[in + j] = Math.min(Math.max(rj, range[2 * j], range[2 * j + 1]));
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}
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}
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return out;
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return y;
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}
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},
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