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GRAPHICS: Switch to integer based JPEG IDCT
Based on public domain code, and explanations from : http://halicery.com/jpeg/idct.html Thanks.
This commit is contained in:
Bastien Bouclet
parent
de0425c7e2
commit
3becde4d1a
@ -43,20 +43,6 @@ static const uint8 _zigZagOrder[64] = {
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53, 60, 61, 54, 47, 55, 62, 63
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};
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// IDCT table built with :
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// _idct8x8[x][y] = cos(((2 * x + 1) * y) * (M_PI / 16.0)) * 0.5;
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// _idct8x8[x][y] /= sqrt(2.0) if y == 0
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static const double _idct8x8[8][8] = {
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{ 0.353553390593274, 0.490392640201615, 0.461939766255643, 0.415734806151273, 0.353553390593274, 0.277785116509801, 0.191341716182545, 0.097545161008064 },
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{ 0.353553390593274, 0.415734806151273, 0.191341716182545, -0.097545161008064, -0.353553390593274, -0.490392640201615, -0.461939766255643, -0.277785116509801 },
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{ 0.353553390593274, 0.277785116509801, -0.191341716182545, -0.490392640201615, -0.353553390593274, 0.097545161008064, 0.461939766255643, 0.415734806151273 },
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{ 0.353553390593274, 0.097545161008064, -0.461939766255643, -0.277785116509801, 0.353553390593274, 0.415734806151273, -0.191341716182545, -0.490392640201615 },
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{ 0.353553390593274, -0.097545161008064, -0.461939766255643, 0.277785116509801, 0.353553390593274, -0.415734806151273, -0.191341716182545, 0.490392640201615 },
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{ 0.353553390593274, -0.277785116509801, -0.191341716182545, 0.490392640201615, -0.353553390593273, -0.097545161008064, 0.461939766255643, -0.415734806151273 },
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{ 0.353553390593274, -0.415734806151273, 0.191341716182545, 0.097545161008064, -0.353553390593274, 0.490392640201615, -0.461939766255643, 0.277785116509801 },
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{ 0.353553390593274, -0.490392640201615, 0.461939766255643, -0.415734806151273, 0.353553390593273, -0.277785116509801, 0.191341716182545, -0.097545161008064 }
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};
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JPEG::JPEG() :
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_stream(NULL), _w(0), _h(0), _numComp(0), _components(NULL), _numScanComp(0),
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_scanComp(NULL), _currentComp(NULL) {
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@ -546,40 +532,63 @@ bool JPEG::readMCU(uint16 xMCU, uint16 yMCU) {
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return ok;
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}
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void JPEG::idct8x8(float result[64], const int16 dct[64]) {
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float tmp[64];
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// triple-butterfly-add (and possible rounding)
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#define xadd3(xa, xb, xc, xd, h) \
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p = xa + xb; \
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n = xa - xb; \
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xa = p + xc + h; \
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xb = n + xd + h; \
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xc = p - xc + h; \
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xd = n - xd + h;
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// butterfly-mul
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#define xmul(xa, xb, k1, k2, sh) \
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n = k1 * (xa + xb); \
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p = xa; \
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xa = (n + (k2 - k1) * xb) >> sh; \
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xb = (n - (k2 + k1) * p) >> sh;
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// IDCT based on public domain code from http://halicery.com/jpeg/idct.html
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void JPEG::idct1D8x8(int32 src[8], int32 dest[64], int32 ps, int32 half) {
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int p, n;
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src[0] <<= 9;
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src[1] <<= 7;
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src[3] *= 181;
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src[4] <<= 9;
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src[5] *= 181;
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src[7] <<= 7;
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// Even part
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xmul(src[6], src[2], 277, 669, 0)
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xadd3(src[0], src[4], src[6], src[2], half)
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// Odd part
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xadd3(src[1], src[7], src[3], src[5], 0)
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xmul(src[5], src[3], 251, 50, 6)
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xmul(src[1], src[7], 213, 142, 6)
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dest[0 * 8] = (src[0] + src[1]) >> ps;
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dest[1 * 8] = (src[4] + src[5]) >> ps;
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dest[2 * 8] = (src[2] + src[3]) >> ps;
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dest[3 * 8] = (src[6] + src[7]) >> ps;
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dest[4 * 8] = (src[6] - src[7]) >> ps;
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dest[5 * 8] = (src[2] - src[3]) >> ps;
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dest[6 * 8] = (src[4] - src[5]) >> ps;
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dest[7 * 8] = (src[0] - src[1]) >> ps;
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}
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void JPEG::idct2D8x8(int32 block[64]) {
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int32 tmp[64];
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// Apply 1D IDCT to rows
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for (int y = 0; y < 8; y++) {
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for (int x = 0; x < 8; x++) {
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tmp[y + x * 8] = dct[0] * _idct8x8[x][0]
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+ dct[1] * _idct8x8[x][1]
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+ dct[2] * _idct8x8[x][2]
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+ dct[3] * _idct8x8[x][3]
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+ dct[4] * _idct8x8[x][4]
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+ dct[5] * _idct8x8[x][5]
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+ dct[6] * _idct8x8[x][6]
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+ dct[7] * _idct8x8[x][7];
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}
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dct += 8;
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}
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for (int i = 0; i < 8; i++)
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idct1D8x8(&block[i * 8], &tmp[i], 9, 1 << 8);
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// Apply 1D IDCT to columns
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for (int x = 0; x < 8; x++) {
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const float *u = tmp + x * 8;
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for (int y = 0; y < 8; y++) {
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result[y * 8 + x] = u[0] * _idct8x8[y][0]
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+ u[1] * _idct8x8[y][1]
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+ u[2] * _idct8x8[y][2]
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+ u[3] * _idct8x8[y][3]
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+ u[4] * _idct8x8[y][4]
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+ u[5] * _idct8x8[y][5]
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+ u[6] * _idct8x8[y][6]
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+ u[7] * _idct8x8[y][7];
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for (int i = 0; i < 8; i++)
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idct1D8x8(&tmp[i * 8], &block[i], 12, 1 << 11);
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}
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}
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}
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bool JPEG::readDataUnit(uint16 x, uint16 y) {
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// Prepare an empty data array
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@ -595,30 +604,29 @@ bool JPEG::readDataUnit(uint16 x, uint16 y) {
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readAC(readData);
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// Calculate the DCT coefficients from the input sequence
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int16 DCT[64];
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int32 block[64];
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for (uint8 i = 0; i < 64; i++) {
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// Dequantize
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int16 val = readData[i];
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int32 val = readData[i];
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int16 quant = _quant[_currentComp->quantTableSelector][i];
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val *= quant;
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// Store the normalized coefficients, undoing the Zig-Zag
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DCT[_zigZagOrder[i]] = val;
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block[_zigZagOrder[i]] = val;
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}
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// Apply the IDCT
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float result[64];
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idct8x8(result, DCT);
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idct2D8x8(block);
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// Level shift to make the values unsigned
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for (int i = 0; i < 64; i++) {
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result[i] = result[i] + 128;
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block[i] = block[i] + 128;
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if (result[i] < 0)
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result[i] = 0;
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if (block[i] < 0)
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block[i] = 0;
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if (result[i] > 255)
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result[i] = 255;
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if (block[i] > 255)
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block[i] = 255;
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}
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// Paint the component surface
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@ -636,7 +644,7 @@ bool JPEG::readDataUnit(uint16 x, uint16 y) {
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for (uint8 i = 0; i < 8; i++) {
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for (uint16 sH = 0; sH < scalingH; sH++) {
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*ptr = (byte)(result[j * 8 + i]);
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*ptr = (byte)(block[j * 8 + i]);
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ptr++;
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}
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}
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@ -118,7 +118,8 @@ private:
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uint8 _bitsNumber;
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// Inverse Discrete Cosine Transformation
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void idct8x8(float dst[64], const int16 src[64]);
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static void idct1D8x8(int32 src[8], int32 dest[64], int32 ps, int32 half);
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static void idct2D8x8(int32 block[64]);
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};
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} // End of Graphics namespace
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