GRAPHICS: Improved JPEG decoder performance
Replaced the 2D IDCT by two 1D IDCT (rows, then columns). JPEG images now decode about twice as fast as they used to. svn-id: r55794
This commit is contained in:
Bastien Bouclet
parent
9149100629
commit
e7a57de38b
2 changed files with 47 additions and 37 deletions
|
|
@ -33,10 +33,6 @@
|
|||
|
||||
namespace Graphics {
|
||||
|
||||
#ifndef M_SQRT2
|
||||
#define M_SQRT2 1.41421356237309504880 /* sqrt(2) */
|
||||
#endif /* M_SQRT2 */
|
||||
|
||||
// Order used to traverse the quantization tables
|
||||
static const uint8 _zigZagOrder[64] = {
|
||||
0, 1, 8, 16, 9, 2, 3, 10,
|
||||
|
|
@ -49,15 +45,18 @@ static const uint8 _zigZagOrder[64] = {
|
|||
53, 60, 61, 54, 47, 55, 62, 63
|
||||
};
|
||||
|
||||
static const double _cosine32[32] = {
|
||||
1.000000000000000, 0.980785280403230, 0.923879532511287, 0.831469612302545,
|
||||
0.707106781186548, 0.555570233019602, 0.382683432365090, 0.195090322016128,
|
||||
0.000000000000000, -0.195090322016128, -0.382683432365090, -0.555570233019602,
|
||||
-0.707106781186547, -0.831469612302545, -0.923879532511287, -0.980785280403230,
|
||||
-1.000000000000000, -0.980785280403230, -0.923879532511287, -0.831469612302545,
|
||||
-0.707106781186548, -0.555570233019602, -0.382683432365090, -0.195090322016129,
|
||||
-0.000000000000000, 0.195090322016128, 0.382683432365090, 0.555570233019602,
|
||||
0.707106781186547, 0.831469612302545, 0.923879532511287, 0.980785280403230
|
||||
// IDCT table built with :
|
||||
// _idct8x8[x][y] = cos(((2 * x + 1) * y) * (PI / 16.0)) * 0.5;
|
||||
// _idct8x8[x][y] /= sqrt(2.0) if y == 0
|
||||
static const double _idct8x8[8][8] = {
|
||||
{ 0.353553390593274, 0.490392640201615, 0.461939766255643, 0.415734806151273, 0.353553390593274, 0.277785116509801, 0.191341716182545, 0.097545161008064 },
|
||||
{ 0.353553390593274, 0.415734806151273, 0.191341716182545, -0.097545161008064, -0.353553390593274, -0.490392640201615, -0.461939766255643, -0.277785116509801 },
|
||||
{ 0.353553390593274, 0.277785116509801, -0.191341716182545, -0.490392640201615, -0.353553390593274, 0.097545161008064, 0.461939766255643, 0.415734806151273 },
|
||||
{ 0.353553390593274, 0.097545161008064, -0.461939766255643, -0.277785116509801, 0.353553390593274, 0.415734806151273, -0.191341716182545, -0.490392640201615 },
|
||||
{ 0.353553390593274, -0.097545161008064, -0.461939766255643, 0.277785116509801, 0.353553390593274, -0.415734806151273, -0.191341716182545, 0.490392640201615 },
|
||||
{ 0.353553390593274, -0.277785116509801, -0.191341716182545, 0.490392640201615, -0.353553390593273, -0.097545161008064, 0.461939766255643, -0.415734806151273 },
|
||||
{ 0.353553390593274, -0.415734806151273, 0.191341716182545, 0.097545161008064, -0.353553390593274, 0.490392640201615, -0.461939766255643, 0.277785116509801 },
|
||||
{ 0.353553390593274, -0.490392640201615, 0.461939766255643, -0.415734806151273, 0.353553390593273, -0.277785116509801, 0.191341716182545, -0.097545161008064 }
|
||||
};
|
||||
|
||||
JPEG::JPEG() :
|
||||
|
|
@ -507,18 +506,39 @@ bool JPEG::readMCU(uint16 xMCU, uint16 yMCU) {
|
|||
return ok;
|
||||
}
|
||||
|
||||
float JPEG::idct(int x, int y, int weight, int fx, int fy) {
|
||||
byte vx_in = ((int32)((2 * x) + 1) * fx) % 32;
|
||||
byte vy_in = ((int32)((2 * y) + 1) * fy) % 32;
|
||||
float ret = (float)weight * _cosine32[vx_in] * _cosine32[vy_in];
|
||||
void JPEG::idct8x8(float result[64], const int16 dct[64]) {
|
||||
float tmp[64];
|
||||
|
||||
if (fx == 0)
|
||||
ret /= (float)M_SQRT2;
|
||||
// Apply 1D IDCT to rows
|
||||
for (int y = 0; y < 8; y++) {
|
||||
for (int x = 0; x < 8; x++) {
|
||||
tmp[y + x * 8] = dct[0] * _idct8x8[x][0]
|
||||
+ dct[1] * _idct8x8[x][1]
|
||||
+ dct[2] * _idct8x8[x][2]
|
||||
+ dct[3] * _idct8x8[x][3]
|
||||
+ dct[4] * _idct8x8[x][4]
|
||||
+ dct[5] * _idct8x8[x][5]
|
||||
+ dct[6] * _idct8x8[x][6]
|
||||
+ dct[7] * _idct8x8[x][7];
|
||||
}
|
||||
|
||||
if (fy == 0)
|
||||
ret /= (float)M_SQRT2;
|
||||
dct += 8;
|
||||
}
|
||||
|
||||
return ret;
|
||||
// Apply 1D IDCT to columns
|
||||
for (int x = 0; x < 8; x++) {
|
||||
const float *u = tmp + x * 8;
|
||||
for (int y = 0; y < 8; y++) {
|
||||
result[y * 8 + x] = u[0] * _idct8x8[y][0]
|
||||
+ u[1] * _idct8x8[y][1]
|
||||
+ u[2] * _idct8x8[y][2]
|
||||
+ u[3] * _idct8x8[y][3]
|
||||
+ u[4] * _idct8x8[y][4]
|
||||
+ u[5] * _idct8x8[y][5]
|
||||
+ u[6] * _idct8x8[y][6]
|
||||
+ u[7] * _idct8x8[y][7];
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
bool JPEG::readDataUnit(uint16 x, uint16 y) {
|
||||
|
|
@ -546,23 +566,13 @@ bool JPEG::readDataUnit(uint16 x, uint16 y) {
|
|||
DCT[_zigZagOrder[i]] = val;
|
||||
}
|
||||
|
||||
// Shortcut the IDCT for DC component
|
||||
// Apply the IDCT
|
||||
float result[64];
|
||||
for (uint8 i = 0; i < 64; i++)
|
||||
result[i] = DCT[0] / 2;
|
||||
|
||||
// Apply the IDCT (PAG31)
|
||||
for (int i = 1; i < 64; i++) {
|
||||
if (DCT[i])
|
||||
for (int _y = 0; _y < 8; _y++)
|
||||
for (int _x = 0; _x < 8; _x++)
|
||||
result[_y * 8 + _x] += idct(_x, _y, DCT[i], i % 8, i / 8);
|
||||
}
|
||||
idct8x8(result, DCT);
|
||||
|
||||
// Level shift to make the values unsigned
|
||||
// Divide by 4 is final part of IDCT
|
||||
for (int i = 0; i < 64; i++) {
|
||||
result[i] = result[i] / 4 + 128;
|
||||
result[i] = result[i] + 128;
|
||||
|
||||
if (result[i] < 0)
|
||||
result[i] = 0;
|
||||
|
|
|
|||
|
|
@ -118,8 +118,8 @@ private:
|
|||
uint8 _bitsData;
|
||||
uint8 _bitsNumber;
|
||||
|
||||
// Discrete Cosine Transformation
|
||||
float idct(int x, int y, int weight, int fx, int fy);
|
||||
// Inverse Discrete Cosine Transformation
|
||||
void idct8x8(float dst[64], const int16 src[64]);
|
||||
};
|
||||
|
||||
} // End of Graphics namespace
|
||||
|
|
|
|||
Loading…
Add table
Add a link
Reference in a new issue