From 667a390d94ad3b3ee706f9598a707376d9604810 Mon Sep 17 00:00:00 2001 From: Willem Jan Palenstijn Date: Fri, 29 Mar 2019 10:57:16 +0100 Subject: Fix scaling for fan/strip projector The strip model for a fan beam geometry wasn't taking pixel magnification into account. Among other things, this resulted in diagonals through rectangles being weighted the same as hor/ver lines. This commit fixes this by scaling each pixel contribution by its magnification on the detector. This is only an approximation (since the magnification isn't constant inside the pixel), but since pixels are usually small, the error is also small. Unfortunately, computing this scaling factor is relatively expensive because it introduces a square root in the inner loop. --- .../astra/FanFlatBeamStripKernelProjector2D.inl | 54 ++++++++++++++++++---- 1 file changed, 46 insertions(+), 8 deletions(-) (limited to 'include') diff --git a/include/astra/FanFlatBeamStripKernelProjector2D.inl b/include/astra/FanFlatBeamStripKernelProjector2D.inl index 732c302..889d0a3 100644 --- a/include/astra/FanFlatBeamStripKernelProjector2D.inl +++ b/include/astra/FanFlatBeamStripKernelProjector2D.inl @@ -109,6 +109,9 @@ void CFanFlatBeamStripKernelProjector2D::projectBlock_internal(int _iProjFrom, i // POLICY: RAY PRIOR if (!p.rayPrior(iRayIndex)) continue; + float32 dist_srcDetPixSquared = projgeom->getSourceDetectorDistance() * projgeom->getSourceDetectorDistance() + + (iDetector + 0.5f - m_pProjectionGeometry->getDetectorCount()*0.5f) * (iDetector + 0.5f - m_pProjectionGeometry->getDetectorCount()*0.5f) * DW * DW; + float32 sin_theta_left, cos_theta_left; float32 sin_theta_right, cos_theta_right; @@ -138,10 +141,11 @@ void CFanFlatBeamStripKernelProjector2D::projectBlock_internal(int _iProjFrom, i float32 inv_cos_theta_left = 1.0f / cos_theta_left; float32 inv_cos_theta_right = 1.0f / cos_theta_right; - float32 updateX_left = sin_theta_left * inv_cos_theta_left; - float32 updateX_right = sin_theta_right * inv_cos_theta_right; + float32 updateX_left = sin_theta_left * inv_cos_theta_left; // tan(theta_left) + float32 updateX_right = sin_theta_right * inv_cos_theta_right; // tan(theta_right) // Precalculate kernel limits + // BUG: If updateX_left > 1 (which can happen if theta_left >= pi/4 > theta), then T_l > U_l, and the expressions for res are no longer correct float32 S_l = -0.5f * updateX_left; if (S_l > 0) {S_l = -S_l;} float32 T_l = -S_l; @@ -185,6 +189,13 @@ void CFanFlatBeamStripKernelProjector2D::projectBlock_internal(int _iProjFrom, i xL += updateX_left; xR += updateX_right; + float32 diffSrcYSquared; + if (switch_t) + diffSrcYSquared = m_pVolumeGeometry->pixelRowToCenterY(row) + cos_theta * projgeom->getOriginSourceDistance(); + else + diffSrcYSquared = m_pVolumeGeometry->pixelRowToCenterY(row) - cos_theta * projgeom->getOriginSourceDistance(); + diffSrcYSquared = diffSrcYSquared * diffSrcYSquared; + // for each affected col for (col = x1L; col <= x1R; ++col) { @@ -199,17 +210,25 @@ void CFanFlatBeamStripKernelProjector2D::projectBlock_internal(int _iProjFrom, i else if (x2R > U_r) res = x2R - (x2R-U_r)*(x2R-U_r)*inv_4T_r; else if (x2R >= T_r) res = x2R; else if (x2R > S_r) res = (x2R-S_r)*(x2R-S_r) * inv_4T_r; - else { x2L -= 1.0f; x2R -= 1.0f; continue; } + else { x2L -= 1.0f; x2R -= 1.0f; p.pixelPosterior(iVolumeIndex); continue; } // left if (x2L <= S_l) {} else if (x2L < T_l) res -= (x2L-S_l)*(x2L-S_l) * inv_4T_l; else if (x2L <= U_l) res -= x2L; else if (x2L < V_l) res -= x2L - (x2L-U_l)*(x2L-U_l)*inv_4T_l; - else { x2L -= 1.0f; x2R -= 1.0f; continue; } + else { x2L -= 1.0f; x2R -= 1.0f; p.pixelPosterior(iVolumeIndex); continue; } + + float32 diffSrcX; + if (switch_t) + diffSrcX = m_pVolumeGeometry->pixelColToCenterX(col) - sin_theta * projgeom->getOriginSourceDistance(); + else + diffSrcX = m_pVolumeGeometry->pixelColToCenterX(col) + sin_theta * projgeom->getOriginSourceDistance(); + + float32 scale = sqrt(dist_srcDetPixSquared / (diffSrcYSquared + diffSrcX * diffSrcX)); // POLICY: ADD - p.addWeight(iRayIndex, iVolumeIndex, PW*PH * res); + p.addWeight(iRayIndex, iVolumeIndex, PW*PH * res * scale); // POLICY: PIXEL POSTERIOR p.pixelPosterior(iVolumeIndex); @@ -238,6 +257,9 @@ void CFanFlatBeamStripKernelProjector2D::projectBlock_internal(int _iProjFrom, i // POLICY: RAY PRIOR if (!p.rayPrior(iRayIndex)) continue; + float32 dist_srcDetPixSquared = projgeom->getSourceDetectorDistance() * projgeom->getSourceDetectorDistance() + + (iDetector + 0.5f - m_pProjectionGeometry->getDetectorCount()*0.5f) * (iDetector + 0.5f - m_pProjectionGeometry->getDetectorCount()*0.5f) * DW * DW; + // get theta_l = alpha_left + theta and theta_r = alpha_right + theta float32 sin_theta_left, cos_theta_left; float32 sin_theta_right, cos_theta_right; @@ -270,6 +292,7 @@ void CFanFlatBeamStripKernelProjector2D::projectBlock_internal(int _iProjFrom, i float32 updateX_right = cos_theta_right * inv_sin_theta_right; // Precalculate kernel limits + // BUG: If updateX_left > 1 (which can happen if theta_left < pi/4 <= theta), then T_l > U_l, and the expressions for res are no longer correct float32 S_l = -0.5f * updateX_left; if (S_l > 0) { S_l = -S_l; } float32 T_l = -S_l; @@ -313,6 +336,13 @@ void CFanFlatBeamStripKernelProjector2D::projectBlock_internal(int _iProjFrom, i xL += updateX_left; xR += updateX_right; + float32 diffSrcXSquared; + if (switch_t) + diffSrcXSquared = m_pVolumeGeometry->pixelColToCenterX(col) - sin_theta * projgeom->getOriginSourceDistance(); + else + diffSrcXSquared = m_pVolumeGeometry->pixelColToCenterX(col) + sin_theta * projgeom->getOriginSourceDistance(); + diffSrcXSquared = diffSrcXSquared * diffSrcXSquared; + // for each affected row for (row = x1L; row <= x1R; ++row) { @@ -328,17 +358,25 @@ void CFanFlatBeamStripKernelProjector2D::projectBlock_internal(int _iProjFrom, i else if (x2R > U_r) res = x2R - (x2R-U_r)*(x2R-U_r)*inv_4T_r; else if (x2R >= T_r) res = x2R; else if (x2R > S_r) res = (x2R-S_r)*(x2R-S_r) * inv_4T_r; - else { x2L -= 1.0f; x2R -= 1.0f; continue; } + else { x2L -= 1.0f; x2R -= 1.0f; p.pixelPosterior(iVolumeIndex); continue; } // left if (x2L <= S_l) {} else if (x2L < T_l) res -= (x2L-S_l)*(x2L-S_l) * inv_4T_l; else if (x2L <= U_l) res -= x2L; else if (x2L < V_l) res -= x2L - (x2L-U_l)*(x2L-U_l)*inv_4T_l; - else { x2L -= 1.0f; x2R -= 1.0f; continue; } + else { x2L -= 1.0f; x2R -= 1.0f; p.pixelPosterior(iVolumeIndex); continue; } + + float32 diffSrcY; + if (switch_t) + diffSrcY = m_pVolumeGeometry->pixelRowToCenterY(row) + cos_theta * projgeom->getOriginSourceDistance(); + else + diffSrcY = m_pVolumeGeometry->pixelRowToCenterY(row) - cos_theta * projgeom->getOriginSourceDistance(); + + float32 scale = sqrt(dist_srcDetPixSquared / (diffSrcXSquared + diffSrcY * diffSrcY)); // POLICY: ADD - p.addWeight(iRayIndex, iVolumeIndex, PW*PH * res); + p.addWeight(iRayIndex, iVolumeIndex, PW*PH * res * scale); // POLICY: PIXEL POSTERIOR p.pixelPosterior(iVolumeIndex); -- cgit v1.2.3