fix [#27746] Black and White Render doesn't work and/or Saves as a Blank screen

convert to grayscale when saving renders rather then only writing the red channel.

source/blender/blenlib/BLI_math_color.h

@@ -70,6 +70,7 @@ unsigned int rgb_to_cpack(float r, float g, float b);
 unsigned int hsv_to_cpack(float h, float s, float v);
 
 float rgb_to_grayscale(float rgb[3]);
+unsigned char rgb_to_grayscale_byte(unsigned char rgb[3]);
 
 /***************** Profile Transformations ********************/
 

source/blender/blenlib/intern/math_color.c

@@ -488,6 +488,11 @@ float rgb_to_grayscale(float rgb[3])
 	return 0.3f*rgb[0] + 0.58f*rgb[1] + 0.12f*rgb[2];
 }
 
+unsigned char rgb_to_grayscale_byte(unsigned char rgb[3])
+{
+	return (76*(unsigned short)rgb[0] + 148*(unsigned short)rgb[1] + 31*(unsigned short)rgb[2]) / 255;
+}
+
 /* ********************************* lift/gamma/gain / ASC-CDL conversion ********************************* */
 
 void lift_gamma_gain_to_asc_cdl(float *lift, float *gamma, float *gain, float *offset, float *slope, float *power)

source/blender/editors/render/render_opengl.c

@@ -220,6 +220,11 @@ static void screen_opengl_render_apply(OGLRender *oglrender)
 		if(oglrender->write_still) {
 			char name[FILE_MAX];
 			int ok;
+
+			if(scene->r.planes == 8) {
+				IMB_color_to_bw(ibuf);
+			}
+
 			BKE_makepicstring(name, scene->r.pic, scene->r.cfra, scene->r.imtype, scene->r.scemode & R_EXTENSION, FALSE);
 			ok= BKE_write_ibuf(ibuf, name, scene->r.imtype, scene->r.subimtype, scene->r.quality); /* no need to stamp here */
 			if(ok)	printf("OpenGL Render written to '%s'\n", name);
@@ -433,6 +438,19 @@ static int screen_opengl_render_anim_step(bContext *C, wmOperator *op)
 	ibuf= BKE_image_acquire_ibuf(oglrender->ima, &oglrender->iuser, &lock);
 
 	if(ibuf) {
+		short ibuf_free= FALSE;
+
+		/* color -> greyscale */
+		/* editing directly would alter the render view */
+		if(scene->r.planes == 8) {
+			ImBuf *ibuf_bw= IMB_dupImBuf(ibuf);
+			IMB_color_to_bw(ibuf_bw);
+			// IMB_freeImBuf(ibuf); /* owned by the image */
+			ibuf= ibuf_bw;
+
+			ibuf_free= TRUE;
+		}
+
 		if(BKE_imtype_is_movie(scene->r.imtype)) {
 			ok= oglrender->mh->append_movie(&scene->r, CFRA, (int*)ibuf->rect, oglrender->sizex, oglrender->sizey, oglrender->reports);
 			if(ok) {
@@ -453,6 +471,10 @@ static int screen_opengl_render_anim_step(bContext *C, wmOperator *op)
 				BKE_reportf(op->reports, RPT_INFO, "Saved file: %s", name);
 			}
 		}
+
+		if(ibuf_free) {
+			IMB_freeImBuf(ibuf);
+		}
 	}
 
 	BKE_image_release_ibuf(oglrender->ima, lock);

source/blender/imbuf/IMB_imbuf.h

@@ -338,6 +338,7 @@ void IMB_float_from_rect_simple(struct ImBuf *ibuf); /* no profile conversion */
 /* note, check that the conversion exists, only some are supported */
 void IMB_convert_profile(struct ImBuf *ibuf, int profile);
 float *IMB_float_profile_ensure(struct ImBuf *ibuf, int profile, int *alloc);
+void IMB_color_to_bw(struct ImBuf *ibuf);
 
 /**
  * Change the ordering of the color bytes pointed to by rect from

source/blender/imbuf/intern/divers.c

@@ -490,3 +490,23 @@ float *IMB_float_profile_ensure(struct ImBuf *ibuf, int profile, int *alloc)
 		return fbuf;
 	}
 }
+
+
+/* no profile conversion */
+void IMB_color_to_bw(struct ImBuf *ibuf)
+{
+	float *rctf= ibuf->rect_float;
+	unsigned char *rct= (unsigned char *)ibuf->rect;
+	int i;
+	if(rctf) {
+		for (i = ibuf->x * ibuf->y; i > 0; i--, rctf+=4) {
+			rctf[0]= rctf[1]= rctf[2]= rgb_to_grayscale(rctf);
+		}
+	}
+
+	if(rct) {
+		for (i = ibuf->x * ibuf->y; i > 0; i--, rct+=4) {
+			rct[0]= rct[1]= rct[2]= rgb_to_grayscale_byte(rct);
+		}
+	}
+}

source/blender/render/intern/source/pipeline.c

@@ -2995,6 +2995,15 @@ static int do_write_image_or_movie(Render *re, Scene *scene, bMovieHandle *mh, R
 				}
 			}
 
+			/* color -> greyscale */
+			/* editing directly would alter the render view */
+			if(scene->r.planes == 8) {
+				ImBuf *ibuf_bw= IMB_dupImBuf(ibuf);
+				IMB_color_to_bw(ibuf_bw);
+				IMB_freeImBuf(ibuf);
+				ibuf= ibuf_bw;
+			}
+
 			ok= BKE_write_ibuf_stamp(scene, camera, ibuf, name, scene->r.imtype, scene->r.subimtype, scene->r.quality);
 			
 			if(ok==0) {