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1
7
8 package com.sun.imageio.plugins.png;
9
10
13 public class RowFilter {
14
15 private static final int abs(int x) {
16 return (x < 0) ? -x : x;
17 }
18
19 protected static int subFilter(byte[] currRow,
21 byte[] subFilteredRow,
22 int bytesPerPixel,
23 int bytesPerRow) {
24 int badness = 0;
25 for (int i = bytesPerPixel; i < bytesPerRow + bytesPerPixel; i++) {
26 int curr = currRow[i] & 0xff;
27 int left = currRow[i - bytesPerPixel] & 0xff;
28 int difference = curr - left;
29 subFilteredRow[i] = (byte)difference;
30
31 badness += abs(difference);
32 }
33
34 return badness;
35 }
36
37 protected static int upFilter(byte[] currRow,
39 byte[] prevRow,
40 byte[] upFilteredRow,
41 int bytesPerPixel,
42 int bytesPerRow) {
43 int badness = 0;
44 for (int i = bytesPerPixel; i < bytesPerRow + bytesPerPixel; i++) {
45 int curr = currRow[i] & 0xff;
46 int up = prevRow[i] & 0xff;
47 int difference = curr - up;
48 upFilteredRow[i] = (byte)difference;
49
50 badness += abs(difference);
51 }
52
53 return badness;
54 }
55
56 protected final int paethPredictor(int a, int b, int c) {
57 int p = a + b - c;
58 int pa = abs(p - a);
59 int pb = abs(p - b);
60 int pc = abs(p - c);
61
62 if ((pa <= pb) && (pa <= pc)) {
63 return a;
64 } else if (pb <= pc) {
65 return b;
66 } else {
67 return c;
68 }
69 }
70
71 public int filterRow(int colorType,
72 byte[] currRow,
73 byte[] prevRow,
74 byte[][] scratchRows,
75 int bytesPerRow,
76 int bytesPerPixel) {
77
78 if (colorType != PNGImageReader.PNG_COLOR_PALETTE) {
80 System.arraycopy(currRow, bytesPerPixel,
81 scratchRows[0], bytesPerPixel,
82 bytesPerRow);
83 return 0;
84 }
85
86 int[] filterBadness = new int[5];
87 for (int i = 0; i < 5; i++) {
88 filterBadness[i] = Integer.MAX_VALUE;
89 }
90
91 {
92 int badness = 0;
93
94 for (int i = bytesPerPixel; i < bytesPerRow + bytesPerPixel; i++) {
95 int curr = currRow[i] & 0xff;
96 badness += curr;
97 }
98
99 filterBadness[0] = badness;
100 }
101
102 {
103 byte[] subFilteredRow = scratchRows[1];
104 int badness = subFilter(currRow,
105 subFilteredRow,
106 bytesPerPixel,
107 bytesPerRow);
108
109 filterBadness[1] = badness;
110 }
111
112 {
113 byte[] upFilteredRow = scratchRows[2];
114 int badness = upFilter(currRow,
115 prevRow,
116 upFilteredRow,
117 bytesPerPixel,
118 bytesPerRow);
119
120 filterBadness[2] = badness;
121 }
122
123 {
124 byte[] averageFilteredRow = scratchRows[3];
125 int badness = 0;
126
127 for (int i = bytesPerPixel; i < bytesPerRow + bytesPerPixel; i++) {
128 int curr = currRow[i] & 0xff;
129 int left = currRow[i - bytesPerPixel] & 0xff;
130 int up = prevRow[i] & 0xff;
131 int difference = curr - (left + up)/2;;
132 averageFilteredRow[i] = (byte)difference;
133
134 badness += abs(difference);
135 }
136
137 filterBadness[3] = badness;
138 }
139
140 {
141 byte[] paethFilteredRow = scratchRows[4];
142 int badness = 0;
143
144 for (int i = bytesPerPixel; i < bytesPerRow + bytesPerPixel; i++) {
145 int curr = currRow[i] & 0xff;
146 int left = currRow[i - bytesPerPixel] & 0xff;
147 int up = prevRow[i] & 0xff;
148 int upleft = prevRow[i - bytesPerPixel] & 0xff;
149 int predictor = paethPredictor(left, up, upleft);
150 int difference = curr - predictor;
151 paethFilteredRow[i] = (byte)difference;
152
153 badness += abs(difference);
154 }
155
156 filterBadness[4] = badness;
157 }
158
159 int minBadness = filterBadness[0];
160 int filterType = 0;
161
162 for (int i = 1; i < 5; i++) {
163 if (filterBadness[i] < minBadness) {
164 minBadness = filterBadness[i];
165 filterType = i;
166 }
167 }
168
169 if (filterType == 0) {
170 System.arraycopy(currRow, bytesPerPixel,
171 scratchRows[0], bytesPerPixel,
172 bytesPerRow);
173 }
174
175 return filterType;
176 }
177 }
178 |
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