1 /*****************************************************************************
2 * Common pixel/chroma manipulation routines.
3 *****************************************************************************
4 * Copyright (C) 2003, 2004 VideoLAN
5 * $Id: pixmap.c,v 1.3 2004/01/31 05:53:35 rocky Exp $
7 * Author: Rocky Bernstein
9 * This program is free software; you can redistribute it and/or modify
10 * it under the terms of the GNU General Public License as published by
11 * the Free Software Foundation; either version 2 of the License, or
12 * (at your option) any later version.
14 * This program is distributed in the hope that it will be useful,
15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 * GNU General Public License for more details.
19 * You should have received a copy of the GNU General Public License
20 * along with this program; if not, write to the Free Software
21 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111, USA.
22 *****************************************************************************/
29 /* FIXME: This is copied from modules/video_chroma/i420_rgb.h.
30 Include from a more common location.
33 /*****************************************************************************
34 * chroma_sys_t: chroma method descriptor
35 *****************************************************************************
36 * This structure is part of the chroma transformation descriptor, it
37 * describes the yuv2rgb specific properties.
38 *****************************************************************************/
44 /* Pre-calculated conversion tables */
45 void *p_base; /* base for all conversion tables */
46 uint8_t *p_rgb8; /* RGB 8 bits table */
47 uint16_t *p_rgb16; /* RGB 16 bits table */
48 uint32_t *p_rgb32; /* RGB 32 bits table */
50 /* To get RGB value for palette entry i, use (p_rgb_r[i], p_rgb_g[i],
53 uint16_t p_rgb_r[CMAP_RGB2_SIZE]; /* Red values of palette */
54 uint16_t p_rgb_g[CMAP_RGB2_SIZE]; /* Green values of palette */
55 uint16_t p_rgb_b[CMAP_RGB2_SIZE]; /* Blue values of palette */
61 http://www.inforamp.net/~poynton/notes/colour_and_gamma/ColorFAQ.html#RTFToC11
62 http://people.ee.ethz.ch/~buc/brechbuehler/mirror/color/ColorFAQ.html#RTFToC1
66 It is useful in a video system to convey a component representative of
67 luminance and two other components representative of colour. It is
68 important to convey the component representative of luminance in such
69 a way that noise (or quantization) introduced in transmission,
70 processing and storage has a perceptually similar effect across the
71 entire tone scale from black to white. The ideal way to accomplish
72 these goals would be to form a luminance signal by matrixing RGB, then
73 subjecting luminance to a nonlinear transfer function similar to the
76 There are practical reasons in video to perform these operations
77 in the opposite order. First a nonlinear transfer function - gamma
78 correction - is applied to each of the linear R, G and B. Then a
79 weighted sum of the nonlinear components is computed to form a
80 signal representative of luminance. The resulting component is
81 related to brightness but is not CIE luminance. Many video
82 engineers call it luma and give it the symbol Y'. It is often
83 carelessly called luminance and given the symbol Y. You must be
84 careful to determine whether a particular author assigns a linear
85 or nonlinear interpretation to the term luminance and the symbol
88 The coefficients that correspond to the "NTSC" red, green and blue
89 CRT phosphors of 1953 are standardized in ITU-R Recommendation BT.
90 601-2 (formerly CCIR Rec. 601-2). I call it Rec. 601. To compute
91 nonlinear video luma from nonlinear red, green and blue:
93 Y'601 = 0.299R' 0.587G' + 0.114B'
95 We will use the integer scaled versions of these numbers below
96 as RED_COEF, GREEN_COEF and BLUE_COEF.
99 /* 19 = round(0.299 * 64) */
100 #define RED_COEF ((int32_t) 19)
102 /* 38 = round(0.587 * 64) */
103 #define GREEN_COEF ((int32_t) 37)
105 /* 7 = round(0.114 * 64) */
106 #define BLUE_COEF ((int32_t) 7)
109 Find the nearest colormap entry in p_vout (assumed to have RGB2
110 chroma, i.e. 256 RGB 8bpp entries) that is closest in color to p_rgb. Set
111 out_rgb to the color found and return the colormap index.
112 INVALID_CMAP_ENTRY is returned if there is some error.
114 The closest match is determined by the the Euclidean distance
115 using integer-scaled 601-2 coefficients described above.
117 Actually, we use the square of the Euclidean distance; but in
118 comparisons it amounts to the same thing.
122 find_cmap_rgb8_nearest(const vout_thread_t *p_vout, const uint8_t *rgb,
130 cmap_t i_bestmatch = INVALID_CMAP_ENTRY;
131 uint32_t i_mindist = 0xFFFFFFFF; /* The largest number here. */
133 /* Check that we really have RGB2. */
135 if ( !p_vout && p_vout->output.i_chroma != VLC_FOURCC('R','G','B','2') )
136 return INVALID_CMAP_ENTRY;
138 p_cmap_r=p_vout->chroma.p_sys->p_rgb_r;
139 p_cmap_g=p_vout->chroma.p_sys->p_rgb_g;
140 p_cmap_b=p_vout->chroma.p_sys->p_rgb_b;
142 for (i = 0; i < CMAP_RGB2_SIZE; i++) {
143 /* Interval range calculations to show that we don't overflow the
144 word sizes below. pixels component values start out 8
145 bits. When we subtract two components we get 9 bits, then
146 square to 10 bits. Next we scale by 6 to give 16
147 bits. XXX_COEF all fit into 5 bits, so when we multiply we
148 should have 21 bits maximum. So computations can be done using
149 32-bit precision. However before storing back distance
150 components we scale back down by 12 bits making the precision 9
151 bits. (This checks out since it is basically the range of the
152 square of the initial 8-bit value.)
154 The squared distance is the sum of three of the 9-bit components
155 described above. This then uses 27-bits and also fits in a
159 /* We use in integer fixed-point fractions rather than floating
160 point for speed. We multiply by 64 (= 1 << 6) before computing
161 the product, and divide the result by 64*64 (= 1 >> (6*2)).
165 #define int32_sqr(x) ( ((int32_t) (x)) * ((int32_t) x) )
167 /* colormap entires are scaled to 16 bits, so we need to shift
168 them back down to 8. */
169 #define CMAP8_RED(i) (p_cmap_r[i]>>8)
170 #define CMAP8_GREEN(i) (p_cmap_g[i]>>8)
171 #define CMAP8_BLUE(i) (p_cmap_b[i]>>8)
173 uint32_t dr = ( RED_COEF * ( int32_sqr(rgb[RED_PIXEL] - CMAP8_RED(i))
174 << SCALEBITS ) ) >> (SCALEBITS*2);
175 uint32_t dg = ( GREEN_COEF * ( int32_sqr(rgb[GREEN_PIXEL] - CMAP8_GREEN(i))
176 << SCALEBITS ) ) >> (SCALEBITS*2);
177 uint32_t db = ( BLUE_COEF * ( int32_sqr(rgb[BLUE_PIXEL] - CMAP8_BLUE(i))
178 << SCALEBITS ) ) >> (SCALEBITS*2);
180 uint32_t i_dist = dr + dg + db;
181 if (i_dist < i_mindist) {
185 printf("+++Change dist to %d RGB cmap %d (%0x, %0x, %0x)\n",
186 i_dist, i, p_cmap_r[ i ], p_cmap_g[ i ], p_cmap_b[ i ]);
193 out_rgb[RED_PIXEL] = CMAP8_RED(i_bestmatch);
194 out_rgb[GREEN_PIXEL] = CMAP8_GREEN(i_bestmatch);
195 out_rgb[BLUE_PIXEL] = CMAP8_BLUE(i_bestmatch);
202 Get the the rgb value for a given colormap entry for p_vout (which is'
203 assumed to have RGB2 chroma).
205 VLC_FALSE is returned if there was some error.
208 query_color(const vout_thread_t *p_vout, cmap_t i_cmap,
209 /*out*/ uint8_t *out_rgb)
215 /* Check that we really have RGB2. */
217 if ( !p_vout && p_vout->output.i_chroma != VLC_FOURCC('R','G','B','2') )
223 p_cmap_r=p_vout->chroma.p_sys->p_rgb_r;
224 p_cmap_g=p_vout->chroma.p_sys->p_rgb_g;
225 p_cmap_b=p_vout->chroma.p_sys->p_rgb_b;
227 out_rgb[RED_PIXEL] = CMAP8_RED(i_cmap);
228 out_rgb[GREEN_PIXEL] = CMAP8_GREEN(i_cmap);
229 out_rgb[BLUE_PIXEL] = CMAP8_BLUE(i_cmap);
237 * c-file-style: "gnu"
239 * indent-tabs-mode: nil