squeeze.h (3446B)
1 // Copyright (c) the JPEG XL Project Authors. All rights reserved. 2 // 3 // Use of this source code is governed by a BSD-style 4 // license that can be found in the LICENSE file. 5 6 #ifndef LIB_JXL_MODULAR_TRANSFORM_SQUEEZE_H_ 7 #define LIB_JXL_MODULAR_TRANSFORM_SQUEEZE_H_ 8 9 // Haar-like transform: halves the resolution in one direction 10 // A B -> (A+B)>>1 in one channel (average) -> same range as 11 // original channel 12 // A-B - tendency in a new channel ('residual' needed to make 13 // the transform reversible) 14 // -> theoretically range could be 2.5 15 // times larger (2 times without the 16 // 'tendency'), but there should be lots 17 // of zeroes 18 // Repeated application (alternating horizontal and vertical squeezes) results 19 // in downscaling 20 // 21 // The default coefficient ordering is low-frequency to high-frequency, as in 22 // M. Antonini, M. Barlaud, P. Mathieu and I. Daubechies, "Image coding using 23 // wavelet transform", IEEE Transactions on Image Processing, vol. 1, no. 2, pp. 24 // 205-220, April 1992, doi: 10.1109/83.136597. 25 26 #include <stdlib.h> 27 28 #include "lib/jxl/base/data_parallel.h" 29 #include "lib/jxl/modular/modular_image.h" 30 #include "lib/jxl/modular/transform/transform.h" 31 32 #define JXL_MAX_FIRST_PREVIEW_SIZE 8 33 34 namespace jxl { 35 36 /* 37 int avg=(A+B)>>1; 38 int diff=(A-B); 39 int rA=(diff+(avg<<1)+(diff&1))>>1; 40 int rB=rA-diff; 41 42 */ 43 // |A B|C D|E F| 44 // p a n p=avg(A,B), a=avg(C,D), n=avg(E,F) 45 // 46 // Goal: estimate C-D (avoiding ringing artifacts) 47 // (ensuring that in smooth areas, a zero residual corresponds to a smooth 48 // gradient) 49 50 // best estimate for C: (B + 2*a)/3 51 // best estimate for D: (n + 3*a)/4 52 // best estimate for C-D: 4*B - 3*n - a /12 53 54 // avoid ringing by 1) only doing this if B <= a <= n or B >= a >= n 55 // (otherwise, this is not a smooth area and we cannot really estimate C-D) 56 // 2) making sure that B <= C <= D <= n or B >= C >= D >= n 57 58 inline pixel_type_w SmoothTendency(pixel_type_w B, pixel_type_w a, 59 pixel_type_w n) { 60 pixel_type_w diff = 0; 61 if (B >= a && a >= n) { 62 diff = (4 * B - 3 * n - a + 6) / 12; 63 // 2C = a<<1 + diff - diff&1 <= 2B so diff - diff&1 <= 2B - 2a 64 // 2D = a<<1 - diff - diff&1 >= 2n so diff + diff&1 <= 2a - 2n 65 if (diff - (diff & 1) > 2 * (B - a)) diff = 2 * (B - a) + 1; 66 if (diff + (diff & 1) > 2 * (a - n)) diff = 2 * (a - n); 67 } else if (B <= a && a <= n) { 68 diff = (4 * B - 3 * n - a - 6) / 12; 69 // 2C = a<<1 + diff + diff&1 >= 2B so diff + diff&1 >= 2B - 2a 70 // 2D = a<<1 - diff + diff&1 <= 2n so diff - diff&1 >= 2a - 2n 71 if (diff + (diff & 1) < 2 * (B - a)) diff = 2 * (B - a) - 1; 72 if (diff - (diff & 1) < 2 * (a - n)) diff = 2 * (a - n); 73 } 74 return diff; 75 } 76 77 void DefaultSqueezeParameters(std::vector<SqueezeParams> *parameters, 78 const Image &image); 79 80 Status CheckMetaSqueezeParams(const SqueezeParams ¶meter, int num_channels); 81 82 Status MetaSqueeze(Image &image, std::vector<SqueezeParams> *parameters); 83 84 Status InvSqueeze(Image &input, const std::vector<SqueezeParams> ¶meters, 85 ThreadPool *pool); 86 87 } // namespace jxl 88 89 #endif // LIB_JXL_MODULAR_TRANSFORM_SQUEEZE_H_