diff --git a/danmaku2ass.py b/danmaku2ass.py
index 9ac3b20..61e2593 100755
--- a/danmaku2ass.py
+++ b/danmaku2ass.py
@@ -511,6 +511,8 @@ def ConvertFlashRotation(rotY, rotZ, X, Y, FOV=math.tan(2*math.pi/9.0)):
         return 180-((180+deg)%360)
     def CalcPerspectiveCorrection(alpha, X, FOV=FOV):
         alpha = WrapAngle(alpha)
+        if FOV is None:
+            return alpha
         if 0 <= alpha <= 180:
             costheta = (FOV*math.cos(alpha*math.pi/180.0)-X*math.sin(alpha*math.pi/180.0))/(FOV+max(2, abs(X)+1)*math.sin(alpha*math.pi/180.0))
             try:
@@ -548,8 +550,8 @@ def ConvertFlashRotation(rotY, rotZ, X, Y, FOV=math.tan(2*math.pi/9.0)):
         outY = math.atan2(-math.sin(rotY)*math.cos(rotZ), math.cos(rotY))*180/math.pi
         outZ = math.atan2(-math.cos(rotY)*math.sin(rotZ), math.cos(rotZ))*180/math.pi
         #outX = math.asin(math.sin(rotY)*math.sin(rotZ))*180/math.pi
-        #outX = math.acos(math.cos(rotY)/math.cos(outY*math.pi/180.0))*180/math.pi
-        outX = math.atan2(-math.sin(rotY)*math.cos(rotZ)*abs(math.cos(outY*math.pi/180.0)*(1 if math.sin(outY*math.pi/180.0) >= 0 else -1)), math.cos(rotY)*abs(math.sin(outY*math.pi/180.0)*(1 if math.cos(outY*math.pi/180.0) >= 0 else -1)))*180/math.pi
+        outX = math.acos(math.cos(rotY)/math.cos(outY*math.pi/180.0))*180/math.pi
+        #outX = math.atan2(-math.sin(rotY)*math.cos(rotZ)*abs(math.cos(outY*math.pi/180.0)*(1 if math.sin(outY*math.pi/180.0) >= 0 else -1)), math.cos(rotY)*abs(math.sin(outY*math.pi/180.0)*(1 if math.cos(outY*math.pi/180.0) >= 0 else -1)))*180/math.pi
         '''
         print(
             (rotY*180.0/math.pi, rotZ*180.0/math.pi),
@@ -560,8 +562,9 @@ def ConvertFlashRotation(rotY, rotZ, X, Y, FOV=math.tan(2*math.pi/9.0)):
             )
         )
         '''
-    outX = CalcPerspectiveCorrection(outX, -Y, FOV*0.75)
-    outY = CalcPerspectiveCorrection(outY, X, FOV)
+    if FOV is not None:
+        outX = CalcPerspectiveCorrection(outX, -Y, FOV*0.75)
+        outY = CalcPerspectiveCorrection(outY, X, FOV)
     return (WrapAngle(round(outX)), WrapAngle(round(outY)), WrapAngle(round(outZ)), 0, round(-0.75*Y*math.sin(outY*math.pi/180.0), 3))
 
 
diff --git a/test/test-3drot.py b/test/test-3drot.py
new file mode 100755
index 0000000..29009b1
--- /dev/null
+++ b/test/test-3drot.py
@@ -0,0 +1,72 @@
+#!/usr/bin/env python3
+
+import logging
+import math
+import sys
+
+try:
+    import importlib.machinery
+    danmaku2ass = importlib.machinery.SourceFileLoader('danmaku2ass', '../danmaku2ass.py').load_module('danmaku2ass')
+except (AttributeError, ImportError):
+    import imp
+    danmaku2ass = imp.load_source('danmaku2ass', '../danmaku2ass..py')
+
+extcode = 0
+
+def main():
+    logging.basicConfig(level=logging.INFO)
+    for rotY in range(0, 361):
+        for rotZ in range(0, 361):
+            outX, outY, outZ, shearX, shearY = danmaku2ass.ConvertFlashRotation(rotY, rotZ, X=0, Y=0, FOV=None)
+            logging.info('%4d, %4d => %4d, %4d, %4d' % (rotY, rotZ, outX, outY, outZ))
+            CompareMatrix(rotY, rotZ, outX, outY, outZ)
+
+def CompareMatrix(rotY, rotZ, outX, outY, outZ):
+    def ApproxEqual(a, b, e=0.01):
+        assert e >= 0
+        a_b = a-b
+        if -e < a_b < e:
+            return 0
+        else:
+            return a_b
+    def FormatError(i, j, l, r):
+        global extcode
+        if ApproxEqual(l, r) != 0:
+            extcode = 1
+            logging.error('l[%s][%s]=%9.6f      r[%s][%s]=%9.6f' % (i, j, l, i, j, r))
+    def sind(x):
+        return math.sin(x*math.pi/180.0)
+    def cosd(x):
+        return math.cos(x*math.pi/180.0)
+
+    l = cosd(rotY)*cosd(rotZ)
+    r = -sind(outX)*sind(outY)*sind(outZ)+cosd(outY)*cosd(outZ)
+    FormatError(0, 0, l, r)
+    l = cosd(rotY)*sind(rotZ)
+    r = -cosd(outX)*sind(outZ)
+    FormatError(0, 1, l, r)
+    l = sind(rotY)
+    r = -sind(outX)*cosd(outY)*sind(outZ)-sind(outY)*cosd(outZ)
+    FormatError(0, 2, l, r)
+    l = -sind(rotZ)
+    r = sind(outX)*sind(outY)*cosd(outZ)+cosd(outY)*sind(outZ)
+    FormatError(1, 0, l, r)
+    l = cosd(rotZ)
+    r = cosd(outX)*cosd(outZ)
+    FormatError(1, 1, l, r)
+    l = 0
+    r = sind(outX)*cosd(outY)*cosd(outZ)-sind(outY)*sind(outZ)
+    FormatError(1, 2, l, r)
+    l = -sind(rotY)*cosd(rotZ)
+    r = cosd(outX)*sind(outY)
+    FormatError(2, 0, l, r)
+    l = -sind(rotY)*sind(rotZ)
+    r = -sind(outX)
+    FormatError(2, 1, l, r)
+    l = cosd(rotY)
+    r = cosd(outX)*cosd(outY)
+    FormatError(2, 2, l, r)
+
+if __name__ == '__main__':
+    main()
+    sys.exit(extcode)