// Initialize IDCT manager.
static void jinit_inverse_dct(jpeg_decompress cinfo)
{
jpeg_lossy_d_codec lossyd = (jpeg_lossy_d_codec)cinfo.coef;
idct_controller idct = null;
try
{
idct = new idct_controller();
}
catch
{
ERREXIT1(cinfo, J_MESSAGE_CODE.JERR_OUT_OF_MEMORY, 4);
}
lossyd.idct_private = idct;
lossyd.idct_start_pass = start_pass_idctmgr;
for (int ci = 0; ci < cinfo.num_components; ci++)
{
jpeg_component_info compptr = cinfo.comp_info[ci];
// Allocate and pre-zero a multiplier table for each component
try
{
compptr.dct_table = new int[DCTSIZE2];
}
catch
{
ERREXIT1(cinfo, J_MESSAGE_CODE.JERR_OUT_OF_MEMORY, 4);
}
// Mark multiplier table not yet set up for any method
idct.cur_method[ci] = -1;
}
}
// Prepare for an output pass.
// Here we select the proper IDCT routine for each component and build
// a matching multiplier table.
static void start_pass_idctmgr(jpeg_decompress cinfo)
{
jpeg_lossy_d_codec lossyd = (jpeg_lossy_d_codec)cinfo.coef;
idct_controller idct = (idct_controller)lossyd.idct_private;
for (int ci = 0; ci < cinfo.num_components; ci++)
{
jpeg_component_info compptr = cinfo.comp_info[ci];
// Select the proper IDCT routine for this component's scaling
lossyd.inverse_DCT[ci] = jpeg_idct_ifast;
// Create multiplier table from quant table.
// However, we can skip this if the component is uninteresting
// or if we already built the table. Also, if no quant table
// has yet been saved for the component, we leave the
// multiplier table all-zero; we'll be reading zeroes from the
// coefficient controller's buffer anyway.
if (!compptr.component_needed || idct.cur_method[ci] == JDCT_IFAST)
{
continue;
}
JQUANT_TBL qtbl = compptr.quant_table;
if (qtbl == null)
{
continue; // happens if no data yet for component
}
idct.cur_method[ci] = JDCT_IFAST;
// For AA&N IDCT method, multipliers are equal to quantization
// coefficients scaled by scalefactor[row]*scalefactor[col], where
// scalefactor[0] = 1
// scalefactor[k] = cos(k*PI/16) * sqrt(2) for k=1..7
// For integer operation, the multiplier table is to be scaled by 2.
int[] ifmtbl = compptr.dct_table;
for (int i = 0; i < DCTSIZE2; i++)
{
ifmtbl[i] = (((int)qtbl.quantval[i] * aanscales[i]) + (1 << 11)) >> 12;
}
}
}
