static void
ditherImage(struct pam * const inpamP,
const scaler * const scalerP,
unsigned int const dithPower,
struct colorResolution const colorRes,
struct pam * const outpamP,
tuple *** const outTuplesP) {
unsigned int const dithDim = 1 << dithPower;
unsigned int const ditherMatrixArea = SQR(dithDim);
unsigned int const modMask = (dithDim - 1);
/* And this into N to compute N % dithDim cheaply, since we
know (though the compiler doesn't) that dithDim is a power of 2
*/
unsigned int ** const ditherMatrix = dithMatrix(dithPower);
tuple * inrow;
tuple ** outTuples;
unsigned int row;
struct pam ditherPam;
/* Describes the tuples that ditherRow() sees */
assert(dithPower < sizeof(unsigned int) * 8);
assert(UINT_MAX / dithDim >= dithDim);
validateNoDitherOverflow(ditherMatrixArea, inpamP, colorRes);
inrow = pnm_allocpamrow(inpamP);
outTuples = pnm_allocpamarray(outpamP);
/* We will modify the input to promote it to depth 3 */
ditherPam = *inpamP;
ditherPam.depth = 3;
for (row = 0; row < inpamP->height; ++row) {
pnm_readpamrow(inpamP, inrow);
pnm_makerowrgb(inpamP, inrow);
ditherRow(&ditherPam, inrow, scalerP, ditherMatrix, ditherMatrixArea,
colorRes, row, modMask,
outpamP, outTuples[row]);
}
free(ditherMatrix);
pnm_freepamrow(inrow);
*outTuplesP = outTuples;
}
// finds a vertical step using a FIR filter, looking for 1 and 2 step intervals between neighboring cols
void findVerticalStep(Mat &src, int col, int fsize, int thresh)
{
char fbuf[fsize];
char fbufn[fsize];
for (int i=0; i<fsize; i++) {fbuf[i] = 0; fbufn[i] = 0;} // init
int tot = 0, totn = 0; // total number of responses
int ind = 0; // end of FIR
int out = 0, outn = 0;
int rows = src.rows;
for (int i=0; i<rows; i++)
{
short* Mi = src.ptr<short>(i);
int diff = Mi[col+1] - Mi[col];
if (diff < 3 && diff > 0)
{
tot++;
fbuf[ind] = diff;
}
if (diff > -3 && diff < 0)
{
totn++;
fbufn[ind] = diff;
}
if (++ind >= fsize) ind = 0;
if (fbuf[ind]!=0) tot--; // fall off the back
if (fbufn[ind]!=0) totn--; // fall off the back
fbuf[ind] = 0; // reset
fbufn[ind] = 0; // reset
// std::cout << Mi[col] << " " << Mi[col+1] << " " << tot << std::endl;
if (tot > thresh)
{
ditherRow(src, col, i-fsize+tot);
out++;
}
if (totn > thresh)
{
ditherRowN(src, col, i-fsize+tot);
outn++;
}
}
// if (out > 0 || outn > 0) std::cout << col << " " << out << " " << outn << std::endl;
}