1 /*****************************************************************************
4 ** Name: backprojectors.cpp Classes for backprojection
5 ** Programmer: Kevin Rosenberg
6 ** Date Started: June 2000
8 ** This is part of the CTSim program
9 ** Copyright (C) 1983-2000 Kevin Rosenberg
11 ** $Id: backprojectors.cpp,v 1.14 2000/09/02 05:10:39 kevin Exp $
13 ** This program is free software; you can redistribute it and/or modify
14 ** it under the terms of the GNU General Public License (version 2) as
15 ** published by the Free Software Foundation.
17 ** This program is distributed in the hope that it will be useful,
18 ** but WITHOUT ANY WARRANTY; without even the implied warranty of
19 ** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 ** GNU General Public License for more details.
22 ** You should have received a copy of the GNU General Public License
23 ** along with this program; if not, write to the Free Software
24 ** Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
25 ******************************************************************************/
29 const int Backprojector::BPROJ_INVALID = -1;
30 const int Backprojector::BPROJ_TRIG = 0;
31 const int Backprojector::BPROJ_TABLE = 1;
32 const int Backprojector::BPROJ_DIFF = 2;
33 const int Backprojector::BPROJ_DIFF2 = 3;
34 const int Backprojector::BPROJ_IDIFF2 = 4;
35 const int Backprojector::BPROJ_IDIFF3 = 5;
37 const char* Backprojector::s_aszBackprojectName[] =
47 const char* Backprojector::s_aszBackprojectTitle[] =
49 {"Direct Trigometric"},
50 {"Trigometric Table"},
51 {"Difference Iteration"},
52 {"Difference Iteration Optimized"},
53 {"Integer Difference Iteration Optimized"},
54 {"Integer Difference Iteration Highly-Optimized"},
57 const int Backprojector::s_iBackprojectCount = sizeof(s_aszBackprojectName) / sizeof(const char*);
59 const int Backprojector::INTERP_INVALID = -1;
60 const int Backprojector::INTERP_NEAREST = 0;
61 const int Backprojector::INTERP_LINEAR = 1;
62 const int Backprojector::INTERP_FREQ_PREINTERPOLATION = 2;
63 #if HAVE_BSPLINE_INTERP
64 const int Backprojector::INTERP_BSPLINE = 3;
65 const int Backprojector::INTERP_1BSPLINE = 4;
66 const int Backprojector::INTERP_2BSPLINE = 5;
67 const int Backprojector::INTERP_3BSPLINE = 6;
70 const char* Backprojector::s_aszInterpName[] =
74 {"freq_preinterpolationj"},
75 #if HAVE_BSPLINE_INTERP
83 const char* Backprojector::s_aszInterpTitle[] =
87 {"Frequency Preinterpolationj"},
88 #if HAVE_BSPLINE_INTERP
90 {"B-Spline 1st Order"},
91 {"B-Spline 2nd Order"},
92 {"B-Spline 3rd Order"},
96 const int Backprojector::s_iInterpCount = sizeof(s_aszInterpName) / sizeof(const char*);
100 Backprojector::Backprojector (const Projections& proj, ImageFile& im, const char* const backprojName, const char* const interpName, const int interpFactor)
103 m_pBackprojectImplem = NULL;
105 initBackprojector (proj, im, backprojName, interpName, interpFactor);
109 Backprojector::BackprojectView (const double* const viewData, const double viewAngle)
111 if (m_pBackprojectImplem != NULL)
112 m_pBackprojectImplem->BackprojectView (viewData, viewAngle);
115 Backprojector::~Backprojector ()
117 delete m_pBackprojectImplem;
120 // FUNCTION IDENTIFICATION
121 // Backproject* projector = selectBackprojector (...)
124 // Selects a backprojector based on BackprojType
125 // and initializes the backprojector
128 Backprojector::initBackprojector (const Projections& proj, ImageFile& im, const char* const backprojName, const char* const interpName, const int interpFactor)
130 m_nameBackproject = backprojName;
131 m_nameInterpolation = interpName;
132 m_pBackprojectImplem = NULL;
133 m_idBackproject = convertBackprojectNameToID (backprojName);
134 if (m_idBackproject == BPROJ_INVALID) {
136 m_failMessage = "Invalid backprojection name ";
137 m_failMessage += backprojName;
139 m_idInterpolation = convertInterpNameToID (interpName);
140 if (m_idInterpolation == INTERP_INVALID) {
142 m_failMessage = "Invalid interpolation name ";
143 m_failMessage += interpName;
146 if (m_fail || m_idBackproject == BPROJ_INVALID || m_idInterpolation == INTERP_INVALID) {
151 if (proj.geometry() == Scanner::GEOMETRY_EQUILINEAR)
152 m_pBackprojectImplem = static_cast<Backproject*>(new BackprojectEquilinear(proj, im, m_idInterpolation, interpFactor));
153 else if (proj.geometry() == Scanner::GEOMETRY_EQUIANGULAR)
154 m_pBackprojectImplem = static_cast<Backproject*>(new BackprojectEquiangular(proj, im, m_idInterpolation, interpFactor));
155 else if (proj.geometry() == Scanner::GEOMETRY_PARALLEL) {
156 if (m_idBackproject == BPROJ_TRIG)
157 m_pBackprojectImplem = static_cast<Backproject*>(new BackprojectTrig (proj, im, m_idInterpolation, interpFactor));
158 else if (m_idBackproject == BPROJ_TABLE)
159 m_pBackprojectImplem = static_cast<Backproject*>(new BackprojectTable (proj, im, m_idInterpolation, interpFactor));
160 else if (m_idBackproject == BPROJ_DIFF)
161 m_pBackprojectImplem = static_cast<Backproject*>(new BackprojectDiff (proj, im, m_idInterpolation, interpFactor));
162 else if (m_idBackproject == BPROJ_DIFF2)
163 m_pBackprojectImplem = static_cast<Backproject*>(new BackprojectDiff2 (proj, im, m_idInterpolation, interpFactor));
164 else if (m_idBackproject == BPROJ_IDIFF2)
165 m_pBackprojectImplem = static_cast<Backproject*>(new BackprojectIntDiff2 (proj, im, m_idInterpolation, interpFactor));
166 else if (m_idBackproject == BPROJ_IDIFF3)
167 m_pBackprojectImplem = static_cast<Backproject*>(new BackprojectIntDiff3 (proj, im, m_idInterpolation, interpFactor));
170 m_failMessage = "Unable to select a backprojection method [Backprojector::initBackprojector]";
179 Backprojector::convertBackprojectNameToID (const char* const backprojName)
181 int backprojID = BPROJ_INVALID;
183 for (int i = 0; i < s_iBackprojectCount; i++)
184 if (strcasecmp (backprojName, s_aszBackprojectName[i]) == 0) {
193 Backprojector::convertBackprojectIDToName (int bprojID)
195 static const char *bprojName = "";
197 if (bprojID >= 0 && bprojID < s_iBackprojectCount)
198 return (s_aszBackprojectName[bprojID]);
204 Backprojector::convertBackprojectIDToTitle (const int bprojID)
206 static const char *bprojTitle = "";
208 if (bprojID >= 0 && bprojID < s_iBackprojectCount)
209 return (s_aszBackprojectTitle[bprojID]);
216 Backprojector::convertInterpNameToID (const char* const interpName)
218 int interpID = INTERP_INVALID;
220 for (int i = 0; i < s_iInterpCount; i++)
221 if (strcasecmp (interpName, s_aszInterpName[i]) == 0) {
230 Backprojector::convertInterpIDToName (const int interpID)
232 static const char *interpName = "";
234 if (interpID >= 0 && interpID < s_iInterpCount)
235 return (s_aszInterpName[interpID]);
241 Backprojector::convertInterpIDToTitle (const int interpID)
243 static const char *interpTitle = "";
245 if (interpID >= 0 && interpID < s_iInterpCount)
246 return (s_aszInterpTitle[interpID]);
248 return (interpTitle);
253 // CLASS IDENTICATION
257 // Pure virtual base class for all backprojectors.
259 Backproject::Backproject (const Projections& proj, ImageFile& im, const int interpType, const int interpFactor)
260 : proj(proj), im(im), interpType(interpType), m_interpFactor(interpFactor)
262 detInc = proj.detInc();
264 iDetCenter = (nDet - 1) / 2; // index refering to L=0 projection
265 rotInc = proj.rotInc();
272 xMin = -proj.phmLen() / 2; // Retangular coords of phantom
273 xMax = xMin + proj.phmLen();
274 yMin = -proj.phmLen() / 2;
275 yMax = yMin + proj.phmLen();
277 xInc = (xMax - xMin) / nx; // size of cells
278 yInc = (yMax - yMin) / ny;
280 m_dFocalLength = proj.focalLength();
283 Backproject::~Backproject ()
287 Backproject::ScaleImageByRotIncrement ()
289 for (int ix = 0; ix < nx; ix++)
290 for (int iy = 0; iy < ny; iy++)
294 void Backproject::errorIndexOutsideDetector (int ix, int iy, double theta, double r, double phi, double L, int iDetPos)
296 sys_error (ERR_WARNING, "r=%f, phi=%f", r, phi);
297 errorIndexOutsideDetector (ix, iy, theta, L, iDetPos);
300 void Backproject::errorIndexOutsideDetector (int ix, int iy, double theta, double L, int iDetPos)
303 os << "ix=" << ix << ", iy=" << iy << ", theta=" << theta << ", L=" << L << ", detinc=" << detInc << "\n";
304 os << "ndet=" << nDet << ", detInc=" << detInc << ", iDetCenter=" << iDetCenter << "\n";
305 os << "xMin=" << xMin << ", xMax=" << xMax << ", xInc=" << xInc << "\n";
306 os << "yMin=" << yMin << ", yMax=" << yMax << ", yInc=" << yInc << "\n";
307 os << "iDetPos index outside bounds: " << iDetPos << " [backprojector]";;
309 sys_error (ERR_WARNING, os.str().c_str());
313 // CLASS IDENTICATION
317 // Uses trigometric functions at each point in image for backprojection.
320 BackprojectTrig::BackprojectView (const double* const filteredProj, const double view_angle)
322 double theta = view_angle;
324 double x = xMin + xInc / 2; // Rectang coords of center of pixel
325 for (int ix = 0; ix < nx; x += xInc, ix++) {
326 double y = yMin + yInc / 2;
327 for (int iy = 0; iy < ny; y += yInc, iy++) {
328 double r = sqrt (x * x + y * y); // distance of cell from center
329 double phi = atan2 (y, x); // angle of cell from center
330 double L = r * cos (theta - phi); // position on detector
332 if (interpType == Backprojector::INTERP_NEAREST) {
333 int iDetPos = iDetCenter + nearest<int> (L / detInc); // calc'd index in the filter raysum array
335 if (iDetPos < 0 || iDetPos >= nDet) // check for impossible: index outside of raysum pos
336 errorIndexOutsideDetector (ix, iy, theta, r, phi, L, iDetPos);
338 v[ix][iy] += rotInc * filteredProj[iDetPos];
339 } else if (interpType == Backprojector::INTERP_LINEAR) {
340 double p = L / detInc; // position along detector
341 double pFloor = floor (p);
342 int iDetPos = iDetCenter + static_cast<int>(pFloor);
343 double frac = p - pFloor; // fraction distance from det
344 if (iDetPos < 0 || iDetPos >= nDet - 1) // check for impossible: index outside of raysum pos
345 errorIndexOutsideDetector (ix, iy, theta, r, phi, L, iDetPos);
347 v[ix][iy] += rotInc * ((1-frac) * filteredProj[iDetPos] + frac * filteredProj[iDetPos+1]);
354 // CLASS IDENTICATION
358 // Precalculates trigometric function value for each point in image for backprojection.
360 BackprojectTable::BackprojectTable (const Projections& proj, ImageFile& im, int interpType, const int interpFactor)
361 : Backproject::Backproject (proj, im, interpType, interpFactor)
363 arrayR.initSetSize (im.nx(), im.ny());
364 arrayPhi.initSetSize (im.nx(), im.ny());
365 r = arrayR.getArray();
366 phi = arrayPhi.getArray();
368 double x, y; // Rectang coords of center of pixel
370 for (x = xMin + xInc / 2, ix = 0; ix < nx; x += xInc, ix++)
371 for (y = yMin + yInc / 2, iy = 0; iy < ny; y += yInc, iy++) {
372 r[ix][iy] = sqrt (x * x + y * y);
373 phi[ix][iy] = atan2 (y, x);
377 BackprojectTable::~BackprojectTable ()
379 ScaleImageByRotIncrement();
383 BackprojectTable::BackprojectView (const double* const filteredProj, const double view_angle)
385 double theta = view_angle;
387 for (int ix = 0; ix < nx; ix++) {
388 ImageFileColumn pImCol = v[ix];
390 for (int iy = 0; iy < ny; iy++) {
391 double L = r[ix][iy] * cos (theta - phi[ix][iy]);
393 if (interpType == Backprojector::INTERP_NEAREST) {
394 int iDetPos = iDetCenter + nearest<int>(L / detInc); // calc index in the filtered raysum vector
396 if (iDetPos < 0 || iDetPos >= nDet) // check for impossible: index outside of raysum pos
397 errorIndexOutsideDetector (ix, iy, theta, r[ix][iy], phi[ix][iy], L, iDetPos);
399 pImCol[iy] += filteredProj[iDetPos];
400 } else if (interpType == Backprojector::INTERP_LINEAR) {
401 double dPos = L / detInc; // position along detector
402 double dPosFloor = floor (dPos);
403 int iDetPos = iDetCenter + static_cast<int>(dPosFloor);
404 double frac = dPos - dPosFloor; // fraction distance from det
405 if (iDetPos < 0 || iDetPos >= nDet - 1)
406 errorIndexOutsideDetector (ix, iy, theta, r[ix][iy], phi[ix][iy], L, iDetPos);
408 pImCol[iy] += ((1-frac) * filteredProj[iDetPos] + frac * filteredProj[iDetPos+1]);
415 // CLASS IDENTICATION
419 // Backprojects by precalculating the change in L position for each x & y step in the image.
420 // Iterates in x & y direction by adding difference in L position
422 BackprojectDiff::BackprojectDiff (const Projections& proj, ImageFile& im, int interpType, const int interpFactor)
423 : Backproject::Backproject (proj, im, interpType, interpFactor)
425 // calculate center of first pixel v[0][0]
426 double x = xMin + xInc / 2;
427 double y = yMin + yInc / 2;
428 start_r = sqrt (x * x + y * y);
429 start_phi = atan2 (y, x);
434 BackprojectDiff::~BackprojectDiff()
436 ScaleImageByRotIncrement();
440 BackprojectDiff::BackprojectView (const double* const filteredProj, const double view_angle)
442 double theta = view_angle; // add half PI to view angle to get perpendicular theta angle
443 double det_dx = xInc * cos (theta);
444 double det_dy = yInc * sin (theta);
445 double lColStart = start_r * cos (theta - start_phi); // calculate L for first point in image
447 for (int ix = 0; ix < nx; ix++, lColStart += det_dx) {
448 double curDetPos = lColStart;
449 ImageFileColumn pImCol = v[ix];
451 for (int iy = 0; iy < ny; iy++, curDetPos += det_dy) {
453 printf ("[%2d,%2d]: %8.5f ", ix, iy, curDetPos);
455 if (interpType == Backprojector::INTERP_NEAREST) {
456 int iDetPos = iDetCenter + nearest<int>(curDetPos / detInc); // calc index in the filtered raysum vector
458 if (iDetPos < 0 || iDetPos >= nDet) // check for impossible: index outside of raysum pos
459 errorIndexOutsideDetector (ix, iy, theta, curDetPos, iDetPos);
461 pImCol[iy] += filteredProj[iDetPos];
462 } else if (interpType == Backprojector::INTERP_LINEAR) {
463 double detPos = curDetPos / detInc; // position along detector
464 double detPosFloor = floor (detPos);
465 int iDetPos = iDetCenter + static_cast<int>(detPosFloor);
466 double frac = detPos - detPosFloor; // fraction distance from det
467 if (iDetPos < 0 || iDetPos >= nDet - 1)
468 errorIndexOutsideDetector (ix, iy, theta, curDetPos, iDetPos);
470 pImCol[iy] += ((1-frac) * filteredProj[iDetPos] + frac * filteredProj[iDetPos+1]);
477 // CLASS IDENTICATION
481 // Optimized version of BackprojectDiff
484 BackprojectDiff2::BackprojectView (const double* const filteredProj, const double view_angle)
486 double theta = view_angle;
488 // Distance betw. detectors for an angle given in units of detectors
489 double det_dx = xInc * cos (theta) / detInc;
490 double det_dy = yInc * sin (theta) / detInc;
492 // calculate detPosition for first point in image (ix=0, iy=0)
493 double detPosColStart = start_r * cos (theta - start_phi) / detInc;
496 printf ("start_r=%8.5f, start_phi=%8.5f, rotInc=%8.5f\n", start_r, start_phi, rotInc);
498 for (int ix = 0; ix < nx; ix++, detPosColStart += det_dx) {
499 double curDetPos = detPosColStart;
500 ImageFileColumn pImCol = v[ix];
502 for (int iy = 0; iy < ny; iy++, curDetPos += det_dy) {
504 printf ("[%2d,%2d]: %8.5f %8.5f\n", ix, iy, curDetPos, filteredProj[iDetCenter + nearest<int>(curDetPos)]);
506 if (interpType == Backprojector::INTERP_NEAREST) {
507 int iDetPos = iDetCenter + nearest<int> (curDetPos); // calc index in the filtered raysum vector
509 if (iDetPos < 0 || iDetPos >= nDet) // check for impossible: index outside of raysum pos
510 errorIndexOutsideDetector (ix, iy, theta, curDetPos, iDetPos);
512 *pImCol++ += filteredProj[iDetPos];
513 } else if (interpType == Backprojector::INTERP_LINEAR) {
514 double detPosFloor = floor (curDetPos);
515 int iDetPos = iDetCenter + static_cast<int>(detPosFloor);
516 double frac = curDetPos - detPosFloor; // fraction distance from det
517 if (iDetPos < 0 || iDetPos >= nDet - 1)
518 errorIndexOutsideDetector (ix, iy, theta, curDetPos, iDetPos);
520 *pImCol++ += filteredProj[iDetPos] + (frac * (filteredProj[iDetPos+1] - filteredProj[iDetPos]));
526 // CLASS IDENTICATION
527 // BackprojectIntDiff2
530 // Integer version of BackprojectDiff2
533 BackprojectIntDiff2::BackprojectView (const double* const filteredProj, const double view_angle)
535 double theta = view_angle;
537 static const kint32 scale = 1 << 16;
538 static const double dScale = scale;
539 static const kint32 halfScale = scale / 2;
541 const kint32 det_dx = nearest<kint32> (xInc * cos (theta) / detInc * scale);
542 const kint32 det_dy = nearest<kint32> (yInc * sin (theta) / detInc * scale);
544 // calculate L for first point in image (0, 0)
545 kint32 detPosColStart = nearest<kint32> (start_r * cos (theta - start_phi) / detInc * scale);
547 for (int ix = 0; ix < nx; ix++, detPosColStart += det_dx) {
548 kint32 curDetPos = detPosColStart;
549 ImageFileColumn pImCol = v[ix];
551 for (int iy = 0; iy < ny; iy++, curDetPos += det_dy) {
552 if (interpType == Backprojector::INTERP_NEAREST) {
553 int detPosNearest = (curDetPos >= 0 ? ((curDetPos + halfScale) / scale) : ((curDetPos - halfScale) / scale));
554 int iDetPos = iDetCenter + detPosNearest; // calc index in the filtered raysum vector
556 if (iDetPos < 0 || iDetPos >= nDet) // check for index outside of raysum pos
557 errorIndexOutsideDetector (ix, iy, theta, curDetPos, iDetPos);
559 *pImCol++ += filteredProj[iDetPos];
560 } else if (interpType == Backprojector::INTERP_LINEAR) {
561 kint32 detPosFloor = curDetPos / scale;
562 kint32 detPosRemainder = curDetPos % scale;
563 if (detPosRemainder < 0) {
565 detPosRemainder += scale;
567 int iDetPos = iDetCenter + detPosFloor;
568 double frac = detPosRemainder / dScale;
569 if (iDetPos < 0 || iDetPos >= nDet - 1)
570 errorIndexOutsideDetector (ix, iy, theta, curDetPos, iDetPos);
572 *pImCol++ += ((1.-frac) * filteredProj[iDetPos] + frac * filteredProj[iDetPos+1]);
578 // CLASS IDENTICATION
579 // BackprojectIntDiff3
582 // Highly optimized version of BackprojectIntDiff2
585 BackprojectIntDiff3::BackprojectView (const double* const filteredProj, const double view_angle)
587 double theta = view_angle; // add half PI to view angle to get perpendicular theta angle
588 static const int scaleShift = 16;
589 static const kint32 scale = (1 << scaleShift);
590 static const kint32 scaleBitmask = scale - 1;
591 static const kint32 halfScale = scale / 2;
592 static const double dInvScale = 1. / scale;
594 const kint32 det_dx = nearest<kint32> (xInc * cos (theta) / detInc * scale);
595 const kint32 det_dy = nearest<kint32> (yInc * sin (theta) / detInc * scale);
597 // calculate L for first point in image (0, 0)
598 kint32 detPosColStart = nearest<kint32> ((start_r * cos (theta - start_phi) / detInc + iDetCenter) * scale);
600 // precalculate scaled difference for linear interpolation
601 double deltaFilteredProj [nDet];
602 if (interpType == Backprojector::INTERP_LINEAR) {
603 for (int i = 0; i < nDet - 1; i++)
604 deltaFilteredProj[i] = (filteredProj[i+1] - filteredProj[i]) * dInvScale;
606 deltaFilteredProj[nDet - 1] = 0; // last detector
608 int iLastDet = nDet - 1;
609 for (int ix = 0; ix < nx; ix++, detPosColStart += det_dx) {
610 kint32 curDetPos = detPosColStart;
611 ImageFileColumn pImCol = v[ix];
613 if (interpType == Backprojector::INTERP_NEAREST) {
614 for (int iy = 0; iy < ny; iy++, curDetPos += det_dy) {
615 const int iDetPos = (curDetPos + halfScale) >> 16;
616 if (iDetPos >= 0 && iDetPos <= iLastDet)
617 *pImCol++ += filteredProj[iDetPos];
619 } else if (interpType == Backprojector::INTERP_FREQ_PREINTERPOLATION) {
620 for (int iy = 0; iy < ny; iy++, curDetPos += det_dy) {
621 const int iDetPos = ((curDetPos + halfScale) >> 16) * m_interpFactor;
622 if (iDetPos >= 0 && iDetPos <= iLastDet)
623 *pImCol++ += filteredProj[iDetPos];
625 } else if (interpType == Backprojector::INTERP_LINEAR) {
626 for (int iy = 0; iy < ny; iy++, curDetPos += det_dy) {
627 const kint32 iDetPos = curDetPos >> scaleShift;
628 const kint32 detRemainder = curDetPos & scaleBitmask;
629 if (iDetPos >= 0 && iDetPos <= iLastDet)
630 *pImCol++ += filteredProj[iDetPos] + (detRemainder * deltaFilteredProj[iDetPos]);
638 BackprojectEquiangular::BackprojectView (const double* const filteredProj, const double view_angle)
640 double beta = view_angle;
642 for (int ix = 0; ix < nx; ix++) {
643 ImageFileColumn pImCol = v[ix];
645 for (int iy = 0; iy < ny; iy++) {
646 double dAngleDiff = beta - phi[ix][iy];
647 double rcos_t = r[ix][iy] * cos (dAngleDiff);
648 double rsin_t = r[ix][iy] * sin (dAngleDiff);
649 double dFLPlusSin = m_dFocalLength + rsin_t;
650 double gamma = atan (rcos_t / dFLPlusSin);
651 double dL2 = dFLPlusSin * dFLPlusSin + (rcos_t * rcos_t);
653 if (interpType == Backprojector::INTERP_NEAREST) {
654 int iDetPos =iDetCenter + nearest<int>(gamma / detInc); // calc index in the filtered raysum vector
656 if (iDetPos < 0 || iDetPos >= nDet) { // check for impossible: index outside of raysum pos
657 ; // errorIndexOutsideDetector (ix, iy, beta, r[ix][iy], phi[ix][iy], gamma, iDetPos);
659 pImCol[iy] += filteredProj[iDetPos] / dL2;
660 } else if (interpType == Backprojector::INTERP_LINEAR) {
661 double dPos = gamma / detInc; // position along detector
662 double dPosFloor = floor (dPos);
663 int iDetPos = iDetCenter + static_cast<int>(dPosFloor);
664 double frac = dPos - dPosFloor; // fraction distance from det
665 if (iDetPos < 0 || iDetPos >= nDet - 1) {
666 ; // errorIndexOutsideDetector (ix, iy, beta, r[ix][iy], phi[ix][iy], gamma, iDetPos);
668 pImCol[iy] += (filteredProj[iDetPos] + frac * (filteredProj[iDetPos+1] - filteredProj[iDetPos])) / dL2;
675 BackprojectEquilinear::BackprojectView (const double* const filteredProj, const double view_angle)
677 double beta = view_angle;
679 for (int ix = 0; ix < nx; ix++) {
680 ImageFileColumn pImCol = v[ix];
682 for (int iy = 0; iy < ny; iy++) {
683 double dAngleDiff = beta - phi[ix][iy];
684 double rcos_t = r[ix][iy] * cos (dAngleDiff);
685 double rsin_t = r[ix][iy] * sin (dAngleDiff);
687 double dU = (m_dFocalLength + rsin_t) / m_dFocalLength;
688 double dDetPos = rcos_t / dU;
689 // double to scale for imaginary detector that passes through origin
690 // of phantom, see Kak-Slaney Figure 3.22
693 if (interpType == Backprojector::INTERP_NEAREST) {
694 int iDetPos = iDetCenter + nearest<int>(dDetPos / detInc); // calc index in the filtered raysum vector
696 if (iDetPos < 0 || iDetPos >= nDet) // check for impossible: index outside of raysum pos
697 ; /// errorIndexOutsideDetector (ix, iy, beta, r[ix][iy], phi[ix][iy], dDetPos, iDetPos);
699 pImCol[iy] += (filteredProj[iDetPos] / (dU * dU));
700 } else if (interpType == Backprojector::INTERP_LINEAR) {
701 double dPos = dDetPos / detInc; // position along detector
702 double dPosFloor = floor (dPos);
703 int iDetPos = iDetCenter + static_cast<int>(dPosFloor);
704 double frac = dPos - dPosFloor; // fraction distance from det
705 if (iDetPos < 0 || iDetPos >= nDet - 1)
706 ; // errorIndexOutsideDetector (ix, iy, beta, r[ix][iy], phi[ix][iy], dDetPos, iDetPos);
708 pImCol[iy] += (filteredProj[iDetPos] + frac * (filteredProj[iDetPos+1] - filteredProj[iDetPos])) / (dU * dU);