| public static DESCALE ( int x, int n ) : int | ||
| x | int | |
| n | int | |
| Результат | int | |
/// <summary>
/// Multiply a DCTELEM variable by an int constant, and immediately
/// descale to yield a DCTELEM result.
/// </summary>
private static int FAST_INTEGER_MULTIPLY(int var, int c)
{
#if !USE_ACCURATE_ROUNDING
return(JpegUtils.RIGHT_SHIFT((var) * (c), FAST_INTEGER_CONST_BITS));
#else
return(JpegUtils.DESCALE((var) * (c), FAST_INTEGER_CONST_BITS));
#endif
}
/// <summary>
/// Perform the forward DCT on one block of samples.
/// NOTE: this code only copes with 8x8 DCTs.
///
/// A slow-but-accurate integer implementation of the
/// forward DCT (Discrete Cosine Transform).
///
/// A 2-D DCT can be done by 1-D DCT on each row followed by 1-D DCT
/// on each column. Direct algorithms are also available, but they are
/// much more complex and seem not to be any faster when reduced to code.
///
/// This implementation is based on an algorithm described in
/// C. Loeffler, A. Ligtenberg and G. Moschytz, "Practical Fast 1-D DCT
/// Algorithms with 11 Multiplications", Proc. Int'l. Conf. on Acoustics,
/// Speech, and Signal Processing 1989 (ICASSP '89), pp. 988-991.
/// The primary algorithm described there uses 11 multiplies and 29 adds.
/// We use their alternate method with 12 multiplies and 32 adds.
/// The advantage of this method is that no data path contains more than one
/// multiplication; this allows a very simple and accurate implementation in
/// scaled fixed-point arithmetic, with a minimal number of shifts.
///
/// The poop on this scaling stuff is as follows:
///
/// Each 1-D DCT step produces outputs which are a factor of sqrt(N)
/// larger than the true DCT outputs. The final outputs are therefore
/// a factor of N larger than desired; since N=8 this can be cured by
/// a simple right shift at the end of the algorithm. The advantage of
/// this arrangement is that we save two multiplications per 1-D DCT,
/// because the y0 and y4 outputs need not be divided by sqrt(N).
/// In the IJG code, this factor of 8 is removed by the quantization
/// step, NOT here.
///
/// We have to do addition and subtraction of the integer inputs, which
/// is no problem, and multiplication by fractional constants, which is
/// a problem to do in integer arithmetic. We multiply all the constants
/// by CONST_SCALE and convert them to integer constants (thus retaining
/// SLOW_INTEGER_CONST_BITS bits of precision in the constants). After doing a
/// multiplication we have to divide the product by CONST_SCALE, with proper
/// rounding, to produce the correct output. This division can be done
/// cheaply as a right shift of SLOW_INTEGER_CONST_BITS bits. We postpone shifting
/// as long as possible so that partial sums can be added together with
/// full fractional precision.
///
/// The outputs of the first pass are scaled up by SLOW_INTEGER_PASS1_BITS bits so that
/// they are represented to better-than-integral precision. These outputs
/// require BITS_IN_JSAMPLE + SLOW_INTEGER_PASS1_BITS + 3 bits; this fits in a 16-bit word
/// with the recommended scaling. (For 12-bit sample data, the intermediate
/// array is int anyway.)
///
/// To avoid overflow of the 32-bit intermediate results in pass 2, we must
/// have BITS_IN_JSAMPLE + SLOW_INTEGER_CONST_BITS + SLOW_INTEGER_PASS1_BITS <= 26. Error analysis
/// shows that the values given below are the most effective.
/// </summary>
private static void jpeg_fdct_islow(int[] data)
{
/* Pass 1: process rows. */
/* Note results are scaled up by sqrt(8) compared to a true DCT; */
/* furthermore, we scale the results by 2**SLOW_INTEGER_PASS1_BITS. */
int dataIndex = 0;
for (int ctr = JpegConstants.DCTSIZE - 1; ctr >= 0; ctr--)
{
int tmp0 = data[dataIndex + 0] + data[dataIndex + 7];
int tmp7 = data[dataIndex + 0] - data[dataIndex + 7];
int tmp1 = data[dataIndex + 1] + data[dataIndex + 6];
int tmp6 = data[dataIndex + 1] - data[dataIndex + 6];
int tmp2 = data[dataIndex + 2] + data[dataIndex + 5];
int tmp5 = data[dataIndex + 2] - data[dataIndex + 5];
int tmp3 = data[dataIndex + 3] + data[dataIndex + 4];
int tmp4 = data[dataIndex + 3] - data[dataIndex + 4];
/* Even part per LL&M figure 1 --- note that published figure is faulty;
* rotator "sqrt(2)*c1" should be "sqrt(2)*c6".
*/
int tmp10 = tmp0 + tmp3;
int tmp13 = tmp0 - tmp3;
int tmp11 = tmp1 + tmp2;
int tmp12 = tmp1 - tmp2;
data[dataIndex + 0] = (tmp10 + tmp11) << SLOW_INTEGER_PASS1_BITS;
data[dataIndex + 4] = (tmp10 - tmp11) << SLOW_INTEGER_PASS1_BITS;
int z1 = (tmp12 + tmp13) * SLOW_INTEGER_FIX_0_541196100;
data[dataIndex + 2] = JpegUtils.DESCALE(z1 + tmp13 * SLOW_INTEGER_FIX_0_765366865,
SLOW_INTEGER_CONST_BITS - SLOW_INTEGER_PASS1_BITS);
data[dataIndex + 6] = JpegUtils.DESCALE(z1 + tmp12 * (-SLOW_INTEGER_FIX_1_847759065),
SLOW_INTEGER_CONST_BITS - SLOW_INTEGER_PASS1_BITS);
/* Odd part per figure 8 --- note paper omits factor of sqrt(2).
* cK represents cos(K*pi/16).
* i0..i3 in the paper are tmp4..tmp7 here.
*/
z1 = tmp4 + tmp7;
int z2 = tmp5 + tmp6;
int z3 = tmp4 + tmp6;
int z4 = tmp5 + tmp7;
int z5 = (z3 + z4) * SLOW_INTEGER_FIX_1_175875602; /* sqrt(2) * c3 */
tmp4 = tmp4 * SLOW_INTEGER_FIX_0_298631336; /* sqrt(2) * (-c1+c3+c5-c7) */
tmp5 = tmp5 * SLOW_INTEGER_FIX_2_053119869; /* sqrt(2) * ( c1+c3-c5+c7) */
tmp6 = tmp6 * SLOW_INTEGER_FIX_3_072711026; /* sqrt(2) * ( c1+c3+c5-c7) */
tmp7 = tmp7 * SLOW_INTEGER_FIX_1_501321110; /* sqrt(2) * ( c1+c3-c5-c7) */
z1 = z1 * (-SLOW_INTEGER_FIX_0_899976223); /* sqrt(2) * (c7-c3) */
z2 = z2 * (-SLOW_INTEGER_FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
z3 = z3 * (-SLOW_INTEGER_FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
z4 = z4 * (-SLOW_INTEGER_FIX_0_390180644); /* sqrt(2) * (c5-c3) */
z3 += z5;
z4 += z5;
data[dataIndex + 7] = JpegUtils.DESCALE(tmp4 + z1 + z3, SLOW_INTEGER_CONST_BITS - SLOW_INTEGER_PASS1_BITS);
data[dataIndex + 5] = JpegUtils.DESCALE(tmp5 + z2 + z4, SLOW_INTEGER_CONST_BITS - SLOW_INTEGER_PASS1_BITS);
data[dataIndex + 3] = JpegUtils.DESCALE(tmp6 + z2 + z3, SLOW_INTEGER_CONST_BITS - SLOW_INTEGER_PASS1_BITS);
data[dataIndex + 1] = JpegUtils.DESCALE(tmp7 + z1 + z4, SLOW_INTEGER_CONST_BITS - SLOW_INTEGER_PASS1_BITS);
dataIndex += JpegConstants.DCTSIZE; /* advance pointer to next row */
}
/* Pass 2: process columns.
* We remove the SLOW_INTEGER_PASS1_BITS scaling, but leave the results scaled up
* by an overall factor of 8.
*/
dataIndex = 0;
for (int ctr = JpegConstants.DCTSIZE - 1; ctr >= 0; ctr--)
{
int tmp0 = data[dataIndex + JpegConstants.DCTSIZE * 0] + data[dataIndex + JpegConstants.DCTSIZE * 7];
int tmp7 = data[dataIndex + JpegConstants.DCTSIZE * 0] - data[dataIndex + JpegConstants.DCTSIZE * 7];
int tmp1 = data[dataIndex + JpegConstants.DCTSIZE * 1] + data[dataIndex + JpegConstants.DCTSIZE * 6];
int tmp6 = data[dataIndex + JpegConstants.DCTSIZE * 1] - data[dataIndex + JpegConstants.DCTSIZE * 6];
int tmp2 = data[dataIndex + JpegConstants.DCTSIZE * 2] + data[dataIndex + JpegConstants.DCTSIZE * 5];
int tmp5 = data[dataIndex + JpegConstants.DCTSIZE * 2] - data[dataIndex + JpegConstants.DCTSIZE * 5];
int tmp3 = data[dataIndex + JpegConstants.DCTSIZE * 3] + data[dataIndex + JpegConstants.DCTSIZE * 4];
int tmp4 = data[dataIndex + JpegConstants.DCTSIZE * 3] - data[dataIndex + JpegConstants.DCTSIZE * 4];
/* Even part per LL&M figure 1 --- note that published figure is faulty;
* rotator "sqrt(2)*c1" should be "sqrt(2)*c6".
*/
int tmp10 = tmp0 + tmp3;
int tmp13 = tmp0 - tmp3;
int tmp11 = tmp1 + tmp2;
int tmp12 = tmp1 - tmp2;
data[dataIndex + JpegConstants.DCTSIZE * 0] = JpegUtils.DESCALE(tmp10 + tmp11, SLOW_INTEGER_PASS1_BITS);
data[dataIndex + JpegConstants.DCTSIZE * 4] = JpegUtils.DESCALE(tmp10 - tmp11, SLOW_INTEGER_PASS1_BITS);
int z1 = (tmp12 + tmp13) * SLOW_INTEGER_FIX_0_541196100;
data[dataIndex + JpegConstants.DCTSIZE * 2] = JpegUtils.DESCALE(z1 + tmp13 * SLOW_INTEGER_FIX_0_765366865,
SLOW_INTEGER_CONST_BITS + SLOW_INTEGER_PASS1_BITS);
data[dataIndex + JpegConstants.DCTSIZE * 6] = JpegUtils.DESCALE(z1 + tmp12 * (-SLOW_INTEGER_FIX_1_847759065),
SLOW_INTEGER_CONST_BITS + SLOW_INTEGER_PASS1_BITS);
/* Odd part per figure 8 --- note paper omits factor of sqrt(2).
* cK represents cos(K*pi/16).
* i0..i3 in the paper are tmp4..tmp7 here.
*/
z1 = tmp4 + tmp7;
int z2 = tmp5 + tmp6;
int z3 = tmp4 + tmp6;
int z4 = tmp5 + tmp7;
int z5 = (z3 + z4) * SLOW_INTEGER_FIX_1_175875602; /* sqrt(2) * c3 */
tmp4 = tmp4 * SLOW_INTEGER_FIX_0_298631336; /* sqrt(2) * (-c1+c3+c5-c7) */
tmp5 = tmp5 * SLOW_INTEGER_FIX_2_053119869; /* sqrt(2) * ( c1+c3-c5+c7) */
tmp6 = tmp6 * SLOW_INTEGER_FIX_3_072711026; /* sqrt(2) * ( c1+c3+c5-c7) */
tmp7 = tmp7 * SLOW_INTEGER_FIX_1_501321110; /* sqrt(2) * ( c1+c3-c5-c7) */
z1 = z1 * (-SLOW_INTEGER_FIX_0_899976223); /* sqrt(2) * (c7-c3) */
z2 = z2 * (-SLOW_INTEGER_FIX_2_562915447); /* sqrt(2) * (-c1-c3) */
z3 = z3 * (-SLOW_INTEGER_FIX_1_961570560); /* sqrt(2) * (-c3-c5) */
z4 = z4 * (-SLOW_INTEGER_FIX_0_390180644); /* sqrt(2) * (c5-c3) */
z3 += z5;
z4 += z5;
data[dataIndex + JpegConstants.DCTSIZE * 7] = JpegUtils.DESCALE(tmp4 + z1 + z3, SLOW_INTEGER_CONST_BITS + SLOW_INTEGER_PASS1_BITS);
data[dataIndex + JpegConstants.DCTSIZE * 5] = JpegUtils.DESCALE(tmp5 + z2 + z4, SLOW_INTEGER_CONST_BITS + SLOW_INTEGER_PASS1_BITS);
data[dataIndex + JpegConstants.DCTSIZE * 3] = JpegUtils.DESCALE(tmp6 + z2 + z3, SLOW_INTEGER_CONST_BITS + SLOW_INTEGER_PASS1_BITS);
data[dataIndex + JpegConstants.DCTSIZE * 1] = JpegUtils.DESCALE(tmp7 + z1 + z4, SLOW_INTEGER_CONST_BITS + SLOW_INTEGER_PASS1_BITS);
dataIndex++; /* advance pointer to next column */
}
}
/// <summary>
/// Initialize for a processing pass.
/// Verify that all referenced Q-tables are present, and set up
/// the divisor table for each one.
/// In the current implementation, DCT of all components is done during
/// the first pass, even if only some components will be output in the
/// first scan. Hence all components should be examined here.
/// </summary>
public virtual void start_pass()
{
for (int ci = 0; ci < m_cinfo.m_num_components; ci++)
{
int qtblno = m_cinfo.Component_info[ci].Quant_tbl_no;
/* Make sure specified quantization table is present */
if (qtblno < 0 || qtblno >= JpegConstants.NUM_QUANT_TBLS || m_cinfo.m_quant_tbl_ptrs[qtblno] == null)
{
m_cinfo.ERREXIT(J_MESSAGE_CODE.JERR_NO_QUANT_TABLE, qtblno);
}
JQUANT_TBL qtbl = m_cinfo.m_quant_tbl_ptrs[qtblno];
/* Compute divisors for this quant table */
/* We may do this more than once for same table, but it's not a big deal */
int i = 0;
switch (m_cinfo.m_dct_method)
{
case J_DCT_METHOD.JDCT_ISLOW:
/* For LL&M IDCT method, divisors are equal to raw quantization
* coefficients multiplied by 8 (to counteract scaling).
*/
if (m_divisors[qtblno] == null)
{
m_divisors[qtblno] = new int [JpegConstants.DCTSIZE2];
}
for (i = 0; i < JpegConstants.DCTSIZE2; i++)
{
m_divisors[qtblno][i] = ((int)qtbl.quantval[i]) << 3;
}
break;
case J_DCT_METHOD.JDCT_IFAST:
if (m_divisors[qtblno] == null)
{
m_divisors[qtblno] = new int [JpegConstants.DCTSIZE2];
}
for (i = 0; i < JpegConstants.DCTSIZE2; i++)
{
m_divisors[qtblno][i] = JpegUtils.DESCALE((int)qtbl.quantval[i] * (int)aanscales[i], CONST_BITS - 3);
}
break;
case J_DCT_METHOD.JDCT_FLOAT:
if (m_float_divisors[qtblno] == null)
{
m_float_divisors[qtblno] = new float [JpegConstants.DCTSIZE2];
}
float[] fdtbl = m_float_divisors[qtblno];
i = 0;
for (int row = 0; row < JpegConstants.DCTSIZE; row++)
{
for (int col = 0; col < JpegConstants.DCTSIZE; col++)
{
fdtbl[i] = (float)(1.0 / (((double)qtbl.quantval[i] * aanscalefactor[row] * aanscalefactor[col] * 8.0)));
i++;
}
}
break;
default:
m_cinfo.ERREXIT(J_MESSAGE_CODE.JERR_NOT_COMPILED);
break;
}
}
}
