Motion blur correction made symmetrical, elimination biases

src/main/java/com/elphel/imagej/gpu/GpuQuad.java

@@ -4364,7 +4364,7 @@ public class GpuQuad{ // quad camera description
 						double dy = mb_vectors[1][nTile];
 						double mb_len = Math.sqrt(dx*dx+dy*dy); // in pixels/s -> 0
 						double [] centerXY_sub = centerXY;
-						if (mb_len < min_len) {
+						if (mb_len < min_len) { // No MB correction
 							tp_task.setScale(1.0);
 							tp_task_sub.task = 0; // disable
 							tp_task_sub.setScale(-min_sub);
@@ -4380,7 +4380,8 @@ public class GpuQuad{ // quad camera description
 							}
 							dx *= mb_offs;
 							dy *= mb_offs;
-							centerXY_sub = new double[] {centerXY[0]+dx,centerXY[1]+dy};
+							centerXY_sub = new double[] {centerXY[0]+0.5*dx,centerXY[1]+0.5*dy};
+							centerXY =     new double[] {centerXY[0]-0.5*dx,centerXY[1]-0.5*dy};
 							tp_task_sub.setCenterXY(centerXY_sub);
 							double exp_offs = Math.exp(-mb_offs/mb_len);
 							double gain =    1.0/(1.0 - exp_offs);