diff --git a/avisynth_prs/draw_prs.cpp b/avisynth_prs/draw_prs.cpp
index e4bb048fa..829288bc2 100644
--- a/avisynth_prs/draw_prs.cpp
+++ b/avisynth_prs/draw_prs.cpp
@@ -85,10 +85,16 @@ PVideoFrame __stdcall DrawPRS::GetFrame(int n, IScriptEnvironment* env) {
 			frame.w = avsFrame->GetRowSize()/4;
 			frame.h = avsFrame->GetHeight();
 			frame.pitch = avsFrame->GetPitch();
-			frame.colorSpace = ColorSpace_RGB32;
 			frame.flipColors = true;
 			frame.flipVertical = true;
 
+			// Set colorspace
+			VideoInfo vi = child->GetVideoInfo();
+			if (vi.IsYV12()) frame.colorSpace = ColorSpace_YV12;
+			else if (vi.IsYUY2()) frame.colorSpace = ColorSpace_YUY2;
+			else if (vi.IsRGB32()) frame.colorSpace = ColorSpace_RGB32;
+			else if (vi.IsRGB24()) frame.colorSpace = ColorSpace_RGB24;
+
 			// Draw into the frame
 			file.DrawFrame(n,&frame);
 		}
diff --git a/prs/prs_specs.txt b/prs/prs_specs.txt
index 450a1b588..385062580 100644
--- a/prs/prs_specs.txt
+++ b/prs/prs_specs.txt
@@ -119,16 +119,16 @@ Start and end frame numbers are both inclusive.
 0x1B	blend mode (8 bit unsigned)
 
 Alpha multiplier:
-0x00 is "invisible",0xFF is "fully visible". This value is multiplied onto
+0x00 is "invisible", 0xFF is "fully visible". This value is multiplied onto
 the alpha value of each pixel in the image to get the actual alpha value for
-that pixel.
+that pixel, that is: finalAlpha = pixelAlpha * globalAlpha / 255;
 
 Blend modes:
-  0	none (dest*(1-alpha) + src*alpha)
-  1	add (dest*(1-alpha) + (src+dest)*alpha)
-  2	subtract (dest*(1-alpha) + (src-dest)*alpha)
-  3	inverse subtract (dest*(1-alpha) + (dest-src)*alpha)
-  4	multiply (dest*(1-alpha) + src*dest*alpha)
+  0	none (src*alpha + dest*(1-alpha))
+  1	add (src*alpha + dest)
+  2	subtract (dest - src*alpha);
+  3	inverse subtract (src*alpha - dest) (is this it?)
+  4	multiply (src*alpha * dst / 255)
 Values are clipped before they are multiplied with alpha.
 
 Layers:
diff --git a/prs/prs_video_frame.cpp b/prs/prs_video_frame.cpp
index ce0cf2f92..697bda676 100644
--- a/prs/prs_video_frame.cpp
+++ b/prs/prs_video_frame.cpp
@@ -77,6 +77,8 @@ PRSVideoFrame::~PRSVideoFrame () {
 
 ///////////////////////////////////
 // Overlay frame on top of another
+// This function could get some optimization/assembly love
+// Also, perhaps using "(x+1) >> 8" instead of "x / 255" should be considered.
 void PRSVideoFrame::Overlay(PRSVideoFrame *dstFrame,int x,int y,unsigned char alpha,unsigned char blend) {
 	// TODO: Colorspace conversion, for now, the function assumes RGB32 on RGB32!
 
@@ -155,6 +157,22 @@ void PRSVideoFrame::Overlay(PRSVideoFrame *dstFrame,int x,int y,unsigned char al
 				*dst++ = MAX(0,(int(dc3) - sc3*a)/255);
 				*dst++ = 255-(ia*(255-da)/255);			// Is this correct?
 			}
+
+			// Inverse subtract blend
+			else if (blend == 3) {
+				*dst++ = MAX(0,(sc1*a - int(dc1))/255);
+				*dst++ = MAX(0,(sc2*a - int(dc2))/255);
+				*dst++ = MAX(0,(sc3*a - int(dc3))/255);
+				*dst++ = 255-(ia*(255-da)/255);			// Is this correct?
+			}
+
+			// Multiply blend
+			else if (blend == 4) {
+				*dst++ = MIN(255,(int(sc1)*a * int(dc1) / 255)/255);
+				*dst++ = MIN(255,(int(sc2)*a * int(dc2) / 255)/255);
+				*dst++ = MIN(255,(int(sc3)*a * int(dc3) / 255)/255);
+				*dst++ = 255-(ia*(255-da)/255);			// Is this correct?
+			}
 		}
 	}
 }