diff --git a/source/blender/include/blendef.h b/source/blender/include/blendef.h
index 45450eb9053..67767cf6613 100644
--- a/source/blender/include/blendef.h
+++ b/source/blender/include/blendef.h
@@ -312,6 +312,9 @@
 #define B_SIMANOTHING		368
 #define B_SIMACURVES		369
 #define B_SIMARANGE			370
+#define B_SIMA_USE_ALPHA	371
+#define B_SIMA_SHOW_ALPHA	372
+#define B_SIMA_SHOW_ZBUF	373
 
 /* BUTS: 400 */
 #define B_BUTSHOME		401
diff --git a/source/blender/makesdna/DNA_space_types.h b/source/blender/makesdna/DNA_space_types.h
index bc5ef2042c2..ed842ad232a 100644
--- a/source/blender/makesdna/DNA_space_types.h
+++ b/source/blender/makesdna/DNA_space_types.h
@@ -467,6 +467,9 @@ typedef struct SpaceImaSel {
 #define SI_PIXELSNAP	1024
 #define SI_LSCM_LIVE	2048
 #define SI_USE_ALPHA	4096
+#define SI_SHOW_ALPHA	8192
+#define SI_SHOW_ZBUF	16384
+
 
 /* SpaceText flags (moved from DNA_text_types.h) */
 
diff --git a/source/blender/src/drawimage.c b/source/blender/src/drawimage.c
index d26a484dba3..8cb8646e21f 100644
--- a/source/blender/src/drawimage.c
+++ b/source/blender/src/drawimage.c
@@ -1099,6 +1099,38 @@ static void sima_draw_alpha_backdrop(SpaceImage *sima, float x1, float y1, float
 	}
 }
 
+static void sima_draw_alpha_pixels(float x1, float y1, int rectx, int recty, unsigned int *recti)
+{
+	char *rect= (char *)recti;
+	
+	/* swap bytes, so alpha is most significant one, then just draw it as luminance int */
+	glPixelStorei(GL_UNPACK_SWAP_BYTES, 1);
+	glaDrawPixelsSafe(x1, y1, rectx, recty, GL_UNSIGNED_INT, recti);
+	glPixelStorei(GL_UNPACK_SWAP_BYTES, 0);
+}
+
+static void sima_draw_zbuf_pixels(float x1, float y1, int rectx, int recty, int *recti)
+{
+	if(recti==NULL)
+		return;
+
+	/* zbuffer values are signed, so we need to shift color range */
+	glPixelTransferf(GL_RED_SCALE, 0.5f);
+	glPixelTransferf(GL_GREEN_SCALE, 0.5f);
+	glPixelTransferf(GL_BLUE_SCALE, 0.5f);
+	glPixelTransferf(GL_RED_BIAS, 0.5f);
+	glPixelTransferf(GL_GREEN_BIAS, 0.5f);
+	glPixelTransferf(GL_BLUE_BIAS, 0.5f);
+	
+	glaDrawPixelsSafe(x1, y1, rectx, recty, GL_INT, recti);
+
+	glPixelTransferf(GL_RED_SCALE, 1.0f);
+	glPixelTransferf(GL_GREEN_SCALE, 1.0f);
+	glPixelTransferf(GL_BLUE_SCALE, 1.0f);
+	glPixelTransferf(GL_RED_BIAS, 0.0f);
+	glPixelTransferf(GL_GREEN_BIAS, 0.0f);
+	glPixelTransferf(GL_BLUE_BIAS, 0.0f);
+}
 
 void drawimagespace(ScrArea *sa, void *spacedata)
 {
@@ -1128,8 +1160,9 @@ void drawimagespace(ScrArea *sa, void *spacedata)
 	what_image(sima);
 	
 	if(sima->image) {
-		if(sima->image->ibuf==0) {
+		if(sima->image->ibuf==NULL) {
 			load_image(sima->image, IB_rect, G.sce, G.scene->r.cfra);
+			scrarea_queue_headredraw(sa);	/* update header for image options */
 		}	
 		tag_image_time(sima->image);
 		ibuf= sima->image->ibuf;
@@ -1208,14 +1241,22 @@ void drawimagespace(ScrArea *sa, void *spacedata)
 				MEM_freeN(rect);
 			}
 			else {
-				if(sima->flag & SI_USE_ALPHA) {
-					sima_draw_alpha_backdrop(sima, x1, y1, (float)ibuf->x, (float)ibuf->y);
-					glEnable(GL_BLEND);
+				if(sima->flag & SI_SHOW_ALPHA) {
+					sima_draw_alpha_pixels(x1, y1, ibuf->x, ibuf->y, ibuf->rect);
+				}
+				else if(sima->flag & SI_SHOW_ZBUF) {
+					sima_draw_zbuf_pixels(x1, y1, ibuf->x, ibuf->y, ibuf->zbuf);
+				}
+				else {
+					if(sima->flag & SI_USE_ALPHA) {
+						sima_draw_alpha_backdrop(sima, x1, y1, (float)ibuf->x, (float)ibuf->y);
+						glEnable(GL_BLEND);
+					}
+					glaDrawPixelsSafe(x1, y1, ibuf->x, ibuf->y, GL_UNSIGNED_BYTE, ibuf->rect);
+					
+					if(sima->flag & SI_USE_ALPHA)
+						glDisable(GL_BLEND);
 				}
-				glaDrawPixelsSafe(x1, y1, ibuf->x, ibuf->y, GL_UNSIGNED_BYTE, ibuf->rect);
-				
-				if(sima->flag & SI_USE_ALPHA)
-					glDisable(GL_BLEND);
 			}
 			
 			if(Gip.current == IMAGEPAINT_CLONE) {
diff --git a/source/blender/src/editsima.c b/source/blender/src/editsima.c
index 2cef5428316..93dab74debc 100644
--- a/source/blender/src/editsima.c
+++ b/source/blender/src/editsima.c
@@ -1398,7 +1398,7 @@ int minmax_tface_uv(float *min, float *max)
 	return sel;
 }
 
-static void sima_show_info(int x, int y, char *cp, float *fp, unsigned int *zp)
+static void sima_show_info(int x, int y, char *cp, float *fp, int *zp)
 {
 	short ofs;
 	char str[256];
@@ -1409,7 +1409,7 @@ static void sima_show_info(int x, int y, char *cp, float *fp, unsigned int *zp)
 	if(fp)
 		ofs+= sprintf(str+ofs, "| R: %.3f G: %.3f B: %.3f A: %.3f ", fp[0], fp[1], fp[2], fp[3]);
 	if(zp)
-		ofs+= sprintf(str+ofs, "| Z: %x ", *zp);
+		ofs+= sprintf(str+ofs, "| Z: %.4f ", 0.5+0.5*( ((float)*zp)/(float)0x7fffffff));
 	
 	glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);
 	glEnable(GL_BLEND);
@@ -1447,7 +1447,7 @@ void sima_sample_color(void)
 			
 			if(fx>=0.0 && fy>=0.0 && fx<1.0 && fy<1.0) {
 				float *fp= NULL;
-				unsigned int *zp= NULL;
+				int *zp= NULL;
 				char *cp= NULL;
 				
 				int x= (int) (fx*ibuf->x);
diff --git a/source/blender/src/glutil.c b/source/blender/src/glutil.c
index ae7cf300844..cc5c2f3c9ec 100644
--- a/source/blender/src/glutil.c
+++ b/source/blender/src/glutil.c
@@ -343,6 +343,10 @@ void glaDrawPixelsSafe(float x, float y, int img_w, int img_h, int format, void
 			float *f_rect= (float *)rect;
 			glDrawPixels(draw_w, draw_h, GL_RGBA, GL_FLOAT, f_rect + (off_y*img_w + off_x)*4);
 		}
+		else if(format==GL_INT || format==GL_UNSIGNED_INT) {
+			int *i_rect= (int *)rect;
+			glDrawPixels(draw_w, draw_h, GL_LUMINANCE, format, i_rect + (off_y*img_w + off_x));
+		}
 		else {
 			unsigned char *uc_rect= (unsigned char *) rect;
 			glDrawPixels(draw_w, draw_h, GL_RGBA, GL_UNSIGNED_BYTE, uc_rect + (off_y*img_w + off_x)*4);
diff --git a/source/blender/src/header_image.c b/source/blender/src/header_image.c
index 7bb7787d40a..29546276fd8 100644
--- a/source/blender/src/header_image.c
+++ b/source/blender/src/header_image.c
@@ -332,6 +332,21 @@ void do_image_buttons(unsigned short event)
 			}
 		}
 		break;
+	case B_SIMA_USE_ALPHA:
+		G.sima->flag &= ~(SI_SHOW_ALPHA|SI_SHOW_ZBUF);
+		scrarea_queue_winredraw(curarea);
+		scrarea_queue_headredraw(curarea);
+		break;
+	case B_SIMA_SHOW_ALPHA:
+		G.sima->flag &= ~(SI_USE_ALPHA|SI_SHOW_ZBUF);
+		scrarea_queue_winredraw(curarea);
+		scrarea_queue_headredraw(curarea);
+		break;
+	case B_SIMA_SHOW_ZBUF:
+		G.sima->flag &= ~(SI_SHOW_ALPHA|SI_USE_ALPHA);
+		scrarea_queue_winredraw(curarea);
+		scrarea_queue_headredraw(curarea);
+		break;
 	}
 }
 
@@ -1166,8 +1181,19 @@ void image_buttons(void)
 		uiDefIconButBitS(block, TOG, SI_DRAWTOOL, B_SIMAGEPAINTTOOL, ICON_TPAINT_HLT, xco,0,XIC,YIC, &G.sima->flag, 0, 0, 0, 0, "Enables painting textures on the image with left mouse button");
 		xco+= XIC+8;
 
-		uiDefIconButBitS(block, TOG, SI_USE_ALPHA, B_REDR, ICON_TRANSP_HLT, xco,0,XIC,YIC, &G.sima->flag, 0, 0, 0, 0, "Draws image with alpha");
-		xco+= XIC+8;
+		uiBlockBeginAlign(block);
+		uiDefIconButBitS(block, TOG, SI_USE_ALPHA, B_SIMA_USE_ALPHA, ICON_TRANSP_HLT, xco,0,XIC,YIC, &G.sima->flag, 0, 0, 0, 0, "Draws image with alpha");
+		xco+= XIC;
+		uiDefIconButBitS(block, TOG, SI_SHOW_ALPHA, B_SIMA_SHOW_ALPHA, ICON_DOT, xco,0,XIC,YIC, &G.sima->flag, 0, 0, 0, 0, "Draws only alpha");
+		xco+= XIC;
+		if(G.sima->image->ibuf &&  G.sima->image->ibuf->zbuf) {
+			uiDefIconButBitS(block, TOG, SI_SHOW_ZBUF, B_SIMA_SHOW_ZBUF, ICON_SOLID, xco,0,XIC,YIC, &G.sima->flag, 0, 0, 0, 0, "Draws zbuffer values");
+			xco+= XIC;
+		}
+		else G.sima->flag &= ~SI_SHOW_ZBUF;	/* no confusing display for non-zbuf images */
+		
+		uiBlockEndAlign(block);
+		xco+= 8;
 	}
 
 	/* draw LOCK */
diff --git a/source/blender/src/renderwin.c b/source/blender/src/renderwin.c
index c629beee9c3..3ffba4c17d0 100644
--- a/source/blender/src/renderwin.c
+++ b/source/blender/src/renderwin.c
@@ -326,16 +326,10 @@ static void renderwin_draw(RenderWin *rw, int just_clear)
 	} else {
 		glPixelZoom(rw->zoom, rw->zoom);
 		if(rw->flags & RW_FLAGS_ALPHA) {
-			char *rect= (char *)R.rectot;
-			
-			glColorMask(1, 0, 0, 0);
-			glaDrawPixelsSafe(disprect[0][0], disprect[0][1], R.rectx, R.recty, GL_UNSIGNED_BYTE, rect+3);
-			glColorMask(0, 1, 0, 0);
-			glaDrawPixelsSafe(disprect[0][0], disprect[0][1], R.rectx, R.recty, GL_UNSIGNED_BYTE, rect+2);
-			glColorMask(0, 0, 1, 0);
-			glaDrawPixelsSafe(disprect[0][0], disprect[0][1], R.rectx, R.recty, GL_UNSIGNED_BYTE, rect+1);
-			glColorMask(1, 1, 1, 1);
-			
+			/* swap bytes, so alpha is most significant one, then just draw it as luminance int */
+			glPixelStorei(GL_UNPACK_SWAP_BYTES, 1);
+			glaDrawPixelsSafe(disprect[0][0], disprect[0][1], R.rectx, R.recty, GL_UNSIGNED_INT, R.rectot);
+			glPixelStorei(GL_UNPACK_SWAP_BYTES, 0);
 		}
 		else {
 			glaDrawPixelsSafe(disprect[0][0], disprect[0][1], R.rectx, R.recty, GL_UNSIGNED_BYTE, R.rectot);