Color:

* Accelerated sRGB <=> linear conversion using lookup table, this can speed up
  loading of images in the compositor and simple renders quite a bit.
* Dithering now uses the Floyd-Steinberg algorithm. Previously it would simply
  randomize each pixel slightly, adding noise, now that should be reduced.

Patch #29309 by David M.

source/blender/blenlib/BLI_math_color.h

@@ -89,6 +89,8 @@ MINLINE void linearrgb_to_srgb_v4(float srgb[4], const float linear[4]);
 MINLINE void srgb_to_linearrgb_predivide_v4(float linear[4], const float srgb[4]);
 MINLINE void linearrgb_to_srgb_predivide_v4(float srgb[4], const float linear[4]);
 
+void BLI_init_srgb_conversion(void);
+
 /************************** Other *************************/
 
 int constrain_rgb(float *r, float *g, float *b);
@@ -97,13 +99,13 @@ void minmax_rgb(short c[3]);
 void rgb_float_set_hue_float_offset(float * rgb, float hue_offset);
 void rgb_byte_set_hue_float_offset(unsigned char * rgb, float hue_offset);
 
+void rgb_byte_to_float(const unsigned char *in, float *out);
+void rgb_float_to_byte(const float *in, unsigned char *out);
+
 /***************** 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);
 
-void rgb_byte_to_float(const unsigned char *in, float *out);
-void rgb_float_to_byte(const float *in, unsigned char *out);
-
 #ifdef BLI_MATH_INLINE_H
 #include "intern/math_color_inline.c"
 #endif

source/blender/blenlib/BLI_utildefines.h

@@ -108,6 +108,7 @@
 
 #define FTOCHAR(val) ((val)<=0.0f)? 0 : (((val)>(1.0f-0.5f/255.0f))? 255 : (char)((255.0f*(val))+0.5f))
 #define FTOUSHORT(val) ((val >= 1.0f-0.5f/65535)? 65535: (val <= 0.0f)? 0: (unsigned short)(val*65535.0f + 0.5f))
+#define USHORTTOUCHAR(val) ((unsigned char)(((val)+0x80)>>8))
 #define F3TOCHAR3(v2, v1) {                                                   \
 		(v1)[0]= FTOCHAR((v2[0]));                                            \
 		(v1)[1]= FTOCHAR((v2[1]));                                            \

source/blender/blenlib/intern/math_color.c

@@ -30,7 +30,11 @@
 
 #include <assert.h>
 
+#include "MEM_guardedalloc.h"
+
 #include "BLI_math.h"
+#include "BLI_rand.h"
+#include "BLI_utildefines.h"
 
 void hsv_to_rgb(float h, float s, float v, float *r, float *g, float *b)
 {
@@ -480,3 +484,79 @@ void rgb_byte_set_hue_float_offset(unsigned char rgb[3], float hue_offset)
 	rgb_float_set_hue_float_offset(rgb_float, hue_offset);
 	rgb_float_to_byte(rgb_float, rgb);
 }
+
+
+/* fast sRGB conversion
+ * LUT from linear float to 16-bit short
+ * based on http://mysite.verizon.net/spitzak/conversion/
+ */
+
+float BLI_color_from_srgb_table[256];
+unsigned short BLI_color_to_srgb_table[0x10000];
+
+static unsigned short hipart(const float f)
+{
+	union {
+		float f;
+		unsigned short us[2];
+	} tmp;
+
+	tmp.f = f;
+
+#ifdef __BIG_ENDIAN__
+	return tmp.us[0];
+#else
+	return tmp.us[1];
+#endif
+}
+
+static float index_to_float(const unsigned short i)
+{
+	union {
+		float f;
+		unsigned short us[2];
+	} tmp;
+
+	/* positive and negative zeros, and all gradual underflow, turn into zero: */
+	if (i<0x80 || (i >= 0x8000 && i < 0x8080)) return 0;
+	/* All NaN's and infinity turn into the largest possible legal float: */
+	if (i>=0x7f80 && i<0x8000) return FLT_MAX;
+	if (i>=0xff80) return -FLT_MAX;
+
+#ifdef __BIG_ENDIAN__
+	tmp.us[0] = i;
+	tmp.us[1] = 0x8000;
+#else
+	tmp.us[0] = 0x8000;
+	tmp.us[1] = i;
+#endif
+
+	return tmp.f;
+}
+
+void BLI_init_srgb_conversion(void)
+{
+	static int initialized= 0;
+	int i, b;
+
+	if (initialized) return;
+	initialized = 1;
+
+	/* Fill in the lookup table to convert floats to bytes: */
+	for (i = 0; i < 0x10000; i++) {
+		float f = linearrgb_to_srgb(index_to_float(i))*255.0f;
+		if (f <= 0) BLI_color_to_srgb_table[i] = 0;
+		else if (f < 255) BLI_color_to_srgb_table[i] = (unsigned short)(f*0x100+.5);
+		else BLI_color_to_srgb_table[i] = 0xff00;
+	}
+
+	/* Fill in the lookup table to convert bytes to float: */
+	for (b = 0; b <= 255; b++) {
+		float f = srgb_to_linearrgb(((float)b)*(1.0f/255.0f));
+		BLI_color_from_srgb_table[b] = f;
+		i = hipart(f);
+		/* replace entries so byte->float->byte does not change the data: */
+		BLI_color_to_srgb_table[i] = b*0x100;
+	}
+}
+

source/blender/blenlib/intern/math_color_inline.c

@@ -105,5 +105,80 @@ MINLINE void linearrgb_to_srgb_predivide_v4(float srgb[4], const float linear[4]
 	srgb[3] = linear[3];
 }
 
+/* LUT accelerated conversions */
+
+extern float BLI_color_from_srgb_table[256];
+extern unsigned short BLI_color_to_srgb_table[0x10000];
+
+MINLINE unsigned short to_srgb_table_lookup(const float f)
+{
+	union {
+		float f;
+		unsigned short us[2];
+	} tmp;
+	tmp.f = f;
+#ifdef __BIG_ENDIAN__
+	return BLI_color_to_srgb_table[tmp.us[0]];
+#else
+	return BLI_color_to_srgb_table[tmp.us[1]];
+#endif
+}
+
+MINLINE void linearrgb_to_srgb_ushort4(unsigned short srgb[4], const float linear[4])
+{
+	srgb[0] = to_srgb_table_lookup(linear[0]);
+	srgb[1] = to_srgb_table_lookup(linear[1]);
+	srgb[2] = to_srgb_table_lookup(linear[2]);
+	srgb[3] = FTOUSHORT(linear[3]);
+}
+
+MINLINE void linearrgb_to_srgb_ushort4_predivide(unsigned short srgb[4], const float linear[4])
+{
+	float alpha, inv_alpha, t;
+	int i;
+
+	if(linear[3] == 1.0f || linear[3] == 0.0f) {
+		linearrgb_to_srgb_ushort4(srgb, linear);
+		return;
+	}
+
+	alpha = linear[3];
+	inv_alpha = 1.0f/alpha;
+
+	for(i=0; i<3; ++i) {
+		t = linear[i] * inv_alpha;
+		srgb[i] = (t < 1.0f)? to_srgb_table_lookup(t) * alpha : FTOUSHORT(linearrgb_to_srgb(t) * alpha);
+	}
+
+	srgb[3] = FTOUSHORT(linear[3]);
+}
+
+MINLINE void srgb_to_linearrgb_uchar4(float linear[4], const unsigned char srgb[4])
+{
+	linear[0] = BLI_color_from_srgb_table[srgb[0]];
+	linear[1] = BLI_color_from_srgb_table[srgb[1]];
+	linear[2] = BLI_color_from_srgb_table[srgb[2]];
+	linear[3] = srgb[3] * (1.0f/255.0f);
+}
+
+MINLINE void srgb_to_linearrgb_uchar4_predivide(float linear[4], const unsigned char srgb[4])
+{
+	float alpha, inv_alpha;
+	int i;
+
+	if(srgb[3] == 255 || srgb[3] == 0) {
+		srgb_to_linearrgb_uchar4(linear, srgb);
+		return;
+	}
+
+	alpha = srgb[3] * (1.0f/255.0f);
+	inv_alpha = 1.0f/alpha;
+
+	for(i=0; i<3; ++i)
+		linear[i] = linearrgb_to_srgb(srgb[i] * inv_alpha) * alpha;
+
+	linear[3] = alpha;
+}
+
 #endif /* BLI_MATH_COLOR_INLINE_H */
 

source/blender/imbuf/intern/divers.c

@@ -46,9 +46,9 @@
 
 /**************************** Interlace/Deinterlace **************************/
 
-void IMB_de_interlace(struct ImBuf *ibuf)
+void IMB_de_interlace(ImBuf *ibuf)
 {
-	struct ImBuf * tbuf1, * tbuf2;
+	ImBuf * tbuf1, * tbuf2;
 	
 	if (ibuf == NULL) return;
 	if (ibuf->flags & IB_fields) return;
@@ -73,9 +73,9 @@ void IMB_de_interlace(struct ImBuf *ibuf)
 	ibuf->y /= 2;
 }
 
-void IMB_interlace(struct ImBuf *ibuf)
+void IMB_interlace(ImBuf *ibuf)
 {
-	struct ImBuf * tbuf1, * tbuf2;
+	ImBuf * tbuf1, * tbuf2;
 
 	if (ibuf == NULL) return;
 	ibuf->flags &= ~IB_fields;
@@ -100,14 +100,76 @@ void IMB_interlace(struct ImBuf *ibuf)
 	}
 }
 
+/************************* Floyd-Steinberg dithering *************************/
+
+typedef struct DitherContext {
+	int *error_buf, *e;
+	int v[4], v0[4], v1[4];
+	float f;
+} DitherContext;
+
+DitherContext *create_dither_context(int w, float factor)
+{
+	DitherContext *di;
+	int i;
+	
+	di= MEM_callocN(sizeof(DitherContext), "dithering context");
+	di->f= factor / 16.0f;
+	di->error_buf= MEM_callocN(4*(w+1)*sizeof(int), "dithering error");
+	di->e= di->error_buf;
+
+	for(i=0; i<4; ++i)
+		di->v[i]= di->v0[i]= di->v1[i]= 1024.0f*(BLI_frand()-0.5f);
+
+	return di;
+}
+
+static void clear_dither_context(DitherContext *di)
+{
+	MEM_freeN(di->error_buf);
+	MEM_freeN(di);
+}
+
+static void dither_finish_row(DitherContext *di)
+{
+	int i;
+
+	for(i=0; i<4; i++)
+		di->v[i]= di->v0[i]= di->v1[i] = 0;
+
+	di->e= di->error_buf;
+}
+
+MINLINE unsigned char dither_value(unsigned short v_in, DitherContext *di, int i)
+{
+	int dv, d2;
+	unsigned char v_out;
+
+	di->v[i] = v_in + (2*di->v[i] + di->e[4]) * di->f;
+	CLAMP(di->v[i], 0, 0xFF00);
+	v_out = USHORTTOUCHAR(di->v[i]);
+	di->v[i] -= v_out<<8;
+	dv = di->v[i];
+	d2 = di->v[i]<<1;
+	di->v[i] += d2;
+	*(di->e++) = di->v[i] + di->v0[i];
+	di->v[i] += d2;
+
+	di->v0[i] = di->v[i] + di->v1[i];
+	di->v1[i] = dv;
+	di->v[i] += d2;
+
+	return v_out;
+}
+
 /************************* Generic Buffer Conversion *************************/
 
 MINLINE void byte_to_float_v4(float f[4], const uchar b[4])
 {
-	f[0] = b[0] * (1.0f/255.0f);
+	f[0]= b[0] * (1.0f/255.0f);
-	f[1] = b[1] * (1.0f/255.0f);
+	f[1]= b[1] * (1.0f/255.0f);
-	f[2] = b[2] * (1.0f/255.0f);
+	f[2]= b[2] * (1.0f/255.0f);
-	f[3] = b[3] * (1.0f/255.0f);
+	f[3]= b[3] * (1.0f/255.0f);
 }
 
 MINLINE void float_to_byte_v4(uchar b[4], const float f[4])
@@ -115,10 +177,26 @@ MINLINE void float_to_byte_v4(uchar b[4], const float f[4])
 	F4TOCHAR4(f, b);
 }
 
-MINLINE void float_to_byte_dither_v4(uchar b[4], const float f[4], float dither)
+MINLINE void ushort_to_byte_v4(uchar b[4], const unsigned short us[4])
 {
-	float tmp[4] = {f[0]+dither, f[1]+dither, f[2]+dither, f[3]+dither};
+	b[0]= USHORTTOUCHAR(us[0]);
-	float_to_byte_v4(b, tmp);
+	b[1]= USHORTTOUCHAR(us[1]);
+	b[2]= USHORTTOUCHAR(us[2]);
+	b[3]= USHORTTOUCHAR(us[3]);
+}
+
+MINLINE void ushort_to_byte_dither_v4(uchar b[4], const unsigned short us[4], DitherContext *di)
+{
+	b[0]= dither_value(us[0], di, 0);
+	b[1]= dither_value(us[0], di, 1);
+	b[2]= dither_value(us[0], di, 2);
+	b[3]= dither_value(us[0], di, 3);
+}
+
+MINLINE void float_to_byte_dither_v4(uchar b[4], const float f[4], DitherContext *di)
+{
+	unsigned short us[4] = {FTOUSHORT(f[0]), FTOUSHORT(f[1]), FTOUSHORT(f[2]), FTOUSHORT(f[3])};
+	ushort_to_byte_dither_v4(b, us, di);
 }
 
 /* float to byte pixels, output 4-channel RGBA */
@@ -127,26 +205,28 @@ void IMB_buffer_byte_from_float(uchar *rect_to, const float *rect_from,
 	int width, int height, int stride_to, int stride_from)
 {
 	float tmp[4];
-	float dither_fac = dither/255.0f;
 	int x, y;
+	DitherContext *di;
 
 	/* we need valid profiles */
 	BLI_assert(profile_to != IB_PROFILE_NONE);
 	BLI_assert(profile_from != IB_PROFILE_NONE);
 
-	if(channels_from==1) {
+	BLI_init_srgb_conversion();
-		/* single channel input */
+	if(dither)
+		di= create_dither_context(width, dither);
+
 	for(y = 0; y < height; y++) {
+		if(channels_from == 1) {
+		/* single channel input */
 			const float *from = rect_from + stride_from*y;
 			uchar *to = rect_to + stride_to*y*4;
 
 			for(x = 0; x < width; x++, from++, to+=4)
 				to[0] = to[1] = to[2] = to[3] = FTOCHAR(from[0]);
 		}
-	}
 		else if(channels_from == 3) {
 		/* RGB input */
-		for(y = 0; y < height; y++) {
 			const float *from = rect_from + stride_from*y*3;
 			uchar *to = rect_to + stride_to*y*4;
 
@@ -174,10 +254,8 @@ void IMB_buffer_byte_from_float(uchar *rect_to, const float *rect_from,
 				}
 			}
 		}
-	}
 		else if(channels_from == 4) {
 		/* RGBA input */
-		for(y = 0; y < height; y++) {
 			const float *from = rect_from + stride_from*y*4;
 			uchar *to = rect_to + stride_to*y*4;
 
@@ -185,7 +263,7 @@ void IMB_buffer_byte_from_float(uchar *rect_to, const float *rect_from,
 				/* no color space conversion */
 				if(dither) {
 					for(x = 0; x < width; x++, from+=4, to+=4)
-						float_to_byte_dither_v4(to, from, (BLI_frand()-0.5f)*dither_fac);
+						float_to_byte_dither_v4(to, from, di);
 				}
 				else {
 					for(x = 0; x < width; x++, from+=4, to+=4)
@@ -194,28 +272,30 @@ void IMB_buffer_byte_from_float(uchar *rect_to, const float *rect_from,
 			}
 			else if(profile_to == IB_PROFILE_SRGB) {
 				/* convert from linear to sRGB */
+				unsigned short us[4];
+
 				if(dither && predivide) {
 					for(x = 0; x < width; x++, from+=4, to+=4) {
-						linearrgb_to_srgb_predivide_v4(tmp, from);
+						linearrgb_to_srgb_ushort4_predivide(us, from);
-						float_to_byte_dither_v4(to, tmp, (BLI_frand()-0.5f)*dither_fac);
+						ushort_to_byte_dither_v4(to, us, di);
 					}
 				}
 				else if(dither) {
 					for(x = 0; x < width; x++, from+=4, to+=4) {
-						linearrgb_to_srgb_v4(tmp, from);
+						linearrgb_to_srgb_ushort4(us, from);
-						float_to_byte_dither_v4(to, tmp, (BLI_frand()-0.5f)*dither_fac);
+						ushort_to_byte_dither_v4(to, us, di);
 					}
 				}
 				else if(predivide) {
 					for(x = 0; x < width; x++, from+=4, to+=4) {
-						linearrgb_to_srgb_predivide_v4(tmp, from);
+						linearrgb_to_srgb_ushort4_predivide(us, from);
-						float_to_byte_v4(to, tmp);
+						ushort_to_byte_v4(to, us);
 					}
 				}
 				else {
 					for(x = 0; x < width; x++, from+=4, to+=4) {
-						linearrgb_to_srgb_v4(tmp, from);
+						linearrgb_to_srgb_ushort4(us, from);
-						float_to_byte_v4(to, tmp);
+						ushort_to_byte_v4(to, us);
 					}
 				}
 			}
@@ -224,13 +304,13 @@ void IMB_buffer_byte_from_float(uchar *rect_to, const float *rect_from,
 				if(dither && predivide) {
 					for(x = 0; x < width; x++, from+=4, to+=4) {
 						srgb_to_linearrgb_predivide_v4(tmp, from);
-						float_to_byte_dither_v4(to, tmp, (BLI_frand()-0.5f)*dither_fac);
+						float_to_byte_dither_v4(to, tmp, di);
 					}
 				}
 				else if(dither) {
 					for(x = 0; x < width; x++, from+=4, to+=4) {
 						srgb_to_linearrgb_v4(tmp, from);
-						float_to_byte_dither_v4(to, tmp, (BLI_frand()-0.5f)*dither_fac);
+						float_to_byte_dither_v4(to, tmp, di);
 					}
 				}
 				else if(predivide) {
@@ -247,7 +327,13 @@ void IMB_buffer_byte_from_float(uchar *rect_to, const float *rect_from,
 				}
 			}
 		}
+
+		if(dither)
+			dither_finish_row(di);
 	}
+
+	if(dither)
+		clear_dither_context(di);
 }
 
 /* byte to float pixels, input and output 4-channel RGBA  */
@@ -262,6 +348,8 @@ void IMB_buffer_float_from_byte(float *rect_to, const uchar *rect_from,
 	BLI_assert(profile_to != IB_PROFILE_NONE);
 	BLI_assert(profile_from != IB_PROFILE_NONE);
 
+	BLI_init_srgb_conversion();
+
 	/* RGBA input */
 	for(y = 0; y < height; y++) {
 		const uchar *from = rect_from + stride_from*y*4;
@@ -276,14 +364,12 @@ void IMB_buffer_float_from_byte(float *rect_to, const uchar *rect_from,
 			/* convert sRGB to linear */
 			if(predivide) {
 				for(x = 0; x < width; x++, from+=4, to+=4) {
-					byte_to_float_v4(tmp, from);
+					srgb_to_linearrgb_uchar4_predivide(to, from);
-					srgb_to_linearrgb_predivide_v4(to, tmp);
 				}
 			}
 			else {
 				for(x = 0; x < width; x++, from+=4, to+=4) {
-					byte_to_float_v4(tmp, from);
+					srgb_to_linearrgb_uchar4(to, from);
-					srgb_to_linearrgb_v4(to, tmp);
 				}
 			}
 		}
@@ -451,7 +537,7 @@ void IMB_buffer_byte_from_byte(uchar *rect_to, const uchar *rect_from,
 
 /****************************** ImBuf Conversion *****************************/
 
-void IMB_rect_from_float(struct ImBuf *ibuf)
+void IMB_rect_from_float(ImBuf *ibuf)
 {
 	int predivide= (ibuf->flags & IB_cm_predivide);
 	int profile_from;
@@ -482,7 +568,7 @@ void IMB_rect_from_float(struct ImBuf *ibuf)
 }
 
 /* converts from linear float to sRGB byte for part of the texture, buffer will hold the changed part */
-void IMB_partial_rect_from_float(struct ImBuf *ibuf, float *buffer, int x, int y, int w, int h)
+void IMB_partial_rect_from_float(ImBuf *ibuf, float *buffer, int x, int y, int w, int h)
 {
 	float *rect_float;
 	uchar *rect_byte;
@@ -521,7 +607,7 @@ void IMB_partial_rect_from_float(struct ImBuf *ibuf, float *buffer, int x, int y
 	ibuf->userflags &= ~IB_RECT_INVALID;
 }
 
-void IMB_float_from_rect(struct ImBuf *ibuf)
+void IMB_float_from_rect(ImBuf *ibuf)
 {
 	int predivide= (ibuf->flags & IB_cm_predivide);
 	int profile_from;
@@ -547,7 +633,7 @@ void IMB_float_from_rect(struct ImBuf *ibuf)
 }
 
 /* no profile conversion */
-void IMB_float_from_rect_simple(struct ImBuf *ibuf)
+void IMB_float_from_rect_simple(ImBuf *ibuf)
 {
 	int predivide= (ibuf->flags & IB_cm_predivide);
 
@@ -559,7 +645,7 @@ void IMB_float_from_rect_simple(struct ImBuf *ibuf)
 		ibuf->x, ibuf->y, ibuf->x, ibuf->x);
 }
 
-void IMB_convert_profile(struct ImBuf *ibuf, int profile)
+void IMB_convert_profile(ImBuf *ibuf, int profile)
 {
 	int predivide= (ibuf->flags & IB_cm_predivide);
 	int profile_from, profile_to;
@@ -601,7 +687,7 @@ void IMB_convert_profile(struct ImBuf *ibuf, int profile)
 
 /* use when you need to get a buffer with a certain profile
  * if the return  */
-float *IMB_float_profile_ensure(struct ImBuf *ibuf, int profile, int *alloc)
+float *IMB_float_profile_ensure(ImBuf *ibuf, int profile, int *alloc)
 {
 	int predivide= (ibuf->flags & IB_cm_predivide);
 	int profile_from, profile_to;
@@ -649,7 +735,7 @@ float *IMB_float_profile_ensure(struct ImBuf *ibuf, int profile, int *alloc)
 /**************************** Color to Grayscale *****************************/
 
 /* no profile conversion */
-void IMB_color_to_bw(struct ImBuf *ibuf)
+void IMB_color_to_bw(ImBuf *ibuf)
 {
 	float *rctf= ibuf->rect_float;
 	uchar *rct= (uchar*)ibuf->rect;