1 | // Copyright 2014 Google Inc. All Rights Reserved. |
2 | // |
3 | // Use of this source code is governed by a BSD-style license |
4 | // that can be found in the COPYING file in the root of the source |
5 | // tree. An additional intellectual property rights grant can be found |
6 | // in the file PATENTS. All contributing project authors may |
7 | // be found in the AUTHORS file in the root of the source tree. |
8 | // ----------------------------------------------------------------------------- |
9 | // |
10 | // Near-lossless image preprocessing adjusts pixel values to help |
11 | // compressibility with a guarantee of maximum deviation between original and |
12 | // resulting pixel values. |
13 | // |
14 | // Author: Jyrki Alakuijala (jyrki@google.com) |
15 | // Converted to C by Aleksander Kramarz (akramarz@google.com) |
16 | |
17 | #include <assert.h> |
18 | #include <stdlib.h> |
19 | |
20 | #include "src/dsp/lossless_common.h" |
21 | #include "src/utils/utils.h" |
22 | #include "src/enc/vp8li_enc.h" |
23 | |
24 | #if (WEBP_NEAR_LOSSLESS == 1) |
25 | |
26 | #define MIN_DIM_FOR_NEAR_LOSSLESS 64 |
27 | #define MAX_LIMIT_BITS 5 |
28 | |
29 | // Quantizes the value up or down to a multiple of 1<<bits (or to 255), |
30 | // choosing the closer one, resolving ties using bankers' rounding. |
31 | static uint32_t FindClosestDiscretized(uint32_t a, int bits) { |
32 | const uint32_t mask = (1u << bits) - 1; |
33 | const uint32_t biased = a + (mask >> 1) + ((a >> bits) & 1); |
34 | assert(bits > 0); |
35 | if (biased > 0xff) return 0xff; |
36 | return biased & ~mask; |
37 | } |
38 | |
39 | // Applies FindClosestDiscretized to all channels of pixel. |
40 | static uint32_t ClosestDiscretizedArgb(uint32_t a, int bits) { |
41 | return |
42 | (FindClosestDiscretized(a >> 24, bits) << 24) | |
43 | (FindClosestDiscretized((a >> 16) & 0xff, bits) << 16) | |
44 | (FindClosestDiscretized((a >> 8) & 0xff, bits) << 8) | |
45 | (FindClosestDiscretized(a & 0xff, bits)); |
46 | } |
47 | |
48 | // Checks if distance between corresponding channel values of pixels a and b |
49 | // is within the given limit. |
50 | static int IsNear(uint32_t a, uint32_t b, int limit) { |
51 | int k; |
52 | for (k = 0; k < 4; ++k) { |
53 | const int delta = |
54 | (int)((a >> (k * 8)) & 0xff) - (int)((b >> (k * 8)) & 0xff); |
55 | if (delta >= limit || delta <= -limit) { |
56 | return 0; |
57 | } |
58 | } |
59 | return 1; |
60 | } |
61 | |
62 | static int IsSmooth(const uint32_t* const prev_row, |
63 | const uint32_t* const curr_row, |
64 | const uint32_t* const next_row, |
65 | int ix, int limit) { |
66 | // Check that all pixels in 4-connected neighborhood are smooth. |
67 | return (IsNear(curr_row[ix], curr_row[ix - 1], limit) && |
68 | IsNear(curr_row[ix], curr_row[ix + 1], limit) && |
69 | IsNear(curr_row[ix], prev_row[ix], limit) && |
70 | IsNear(curr_row[ix], next_row[ix], limit)); |
71 | } |
72 | |
73 | // Adjusts pixel values of image with given maximum error. |
74 | static void NearLossless(int xsize, int ysize, const uint32_t* argb_src, |
75 | int stride, int limit_bits, uint32_t* copy_buffer, |
76 | uint32_t* argb_dst) { |
77 | int x, y; |
78 | const int limit = 1 << limit_bits; |
79 | uint32_t* prev_row = copy_buffer; |
80 | uint32_t* curr_row = prev_row + xsize; |
81 | uint32_t* next_row = curr_row + xsize; |
82 | memcpy(curr_row, argb_src, xsize * sizeof(argb_src[0])); |
83 | memcpy(next_row, argb_src + stride, xsize * sizeof(argb_src[0])); |
84 | |
85 | for (y = 0; y < ysize; ++y, argb_src += stride, argb_dst += xsize) { |
86 | if (y == 0 || y == ysize - 1) { |
87 | memcpy(argb_dst, argb_src, xsize * sizeof(argb_src[0])); |
88 | } else { |
89 | memcpy(next_row, argb_src + stride, xsize * sizeof(argb_src[0])); |
90 | argb_dst[0] = argb_src[0]; |
91 | argb_dst[xsize - 1] = argb_src[xsize - 1]; |
92 | for (x = 1; x < xsize - 1; ++x) { |
93 | if (IsSmooth(prev_row, curr_row, next_row, x, limit)) { |
94 | argb_dst[x] = curr_row[x]; |
95 | } else { |
96 | argb_dst[x] = ClosestDiscretizedArgb(curr_row[x], limit_bits); |
97 | } |
98 | } |
99 | } |
100 | { |
101 | // Three-way swap. |
102 | uint32_t* const temp = prev_row; |
103 | prev_row = curr_row; |
104 | curr_row = next_row; |
105 | next_row = temp; |
106 | } |
107 | } |
108 | } |
109 | |
110 | int VP8ApplyNearLossless(const WebPPicture* const picture, int quality, |
111 | uint32_t* const argb_dst) { |
112 | int i; |
113 | const int xsize = picture->width; |
114 | const int ysize = picture->height; |
115 | const int stride = picture->argb_stride; |
116 | uint32_t* const copy_buffer = |
117 | (uint32_t*)WebPSafeMalloc(xsize * 3, sizeof(*copy_buffer)); |
118 | const int limit_bits = VP8LNearLosslessBits(quality); |
119 | assert(argb_dst != NULL); |
120 | assert(limit_bits > 0); |
121 | assert(limit_bits <= MAX_LIMIT_BITS); |
122 | if (copy_buffer == NULL) { |
123 | return 0; |
124 | } |
125 | // For small icon images, don't attempt to apply near-lossless compression. |
126 | if ((xsize < MIN_DIM_FOR_NEAR_LOSSLESS && |
127 | ysize < MIN_DIM_FOR_NEAR_LOSSLESS) || |
128 | ysize < 3) { |
129 | for (i = 0; i < ysize; ++i) { |
130 | memcpy(argb_dst + i * xsize, picture->argb + i * picture->argb_stride, |
131 | xsize * sizeof(*argb_dst)); |
132 | } |
133 | WebPSafeFree(copy_buffer); |
134 | return 1; |
135 | } |
136 | |
137 | NearLossless(xsize, ysize, picture->argb, stride, limit_bits, copy_buffer, |
138 | argb_dst); |
139 | for (i = limit_bits - 1; i != 0; --i) { |
140 | NearLossless(xsize, ysize, argb_dst, xsize, i, copy_buffer, argb_dst); |
141 | } |
142 | WebPSafeFree(copy_buffer); |
143 | return 1; |
144 | } |
145 | #else // (WEBP_NEAR_LOSSLESS == 1) |
146 | |
147 | // Define a stub to suppress compiler warnings. |
148 | extern void VP8LNearLosslessStub(void); |
149 | void VP8LNearLosslessStub(void) {} |
150 | |
151 | #endif // (WEBP_NEAR_LOSSLESS == 1) |
152 | |