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// Copyright (c) the JPEG XL Project Authors. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
#ifndef LIB_JXL_MODULAR_TRANSFORM_SQUEEZE_H_
#define LIB_JXL_MODULAR_TRANSFORM_SQUEEZE_H_
// Haar-like transform: halves the resolution in one direction
// A B -> (A+B)>>1 in one channel (average) -> same range as
// original channel
// A-B - tendency in a new channel ('residual' needed to make
// the transform reversible)
// -> theoretically range could be 2.5
// times larger (2 times without the
// 'tendency'), but there should be lots
// of zeroes
// Repeated application (alternating horizontal and vertical squeezes) results
// in downscaling
//
// The default coefficient ordering is low-frequency to high-frequency, as in
// M. Antonini, M. Barlaud, P. Mathieu and I. Daubechies, "Image coding using
// wavelet transform", IEEE Transactions on Image Processing, vol. 1, no. 2, pp.
// 205-220, April 1992, doi: 10.1109/83.136597.
#include <stdlib.h>
#include "lib/jxl/base/data_parallel.h"
#include "lib/jxl/modular/modular_image.h"
#include "lib/jxl/modular/transform/transform.h"
#define JXL_MAX_FIRST_PREVIEW_SIZE 8
namespace jxl {
/*
int avg=(A+B)>>1;
int diff=(A-B);
int rA=(diff+(avg<<1)+(diff&1))>>1;
int rB=rA-diff;
*/
// |A B|C D|E F|
// p a n p=avg(A,B), a=avg(C,D), n=avg(E,F)
//
// Goal: estimate C-D (avoiding ringing artifacts)
// (ensuring that in smooth areas, a zero residual corresponds to a smooth
// gradient)
// best estimate for C: (B + 2*a)/3
// best estimate for D: (n + 3*a)/4
// best estimate for C-D: 4*B - 3*n - a /12
// avoid ringing by 1) only doing this if B <= a <= n or B >= a >= n
// (otherwise, this is not a smooth area and we cannot really estimate C-D)
// 2) making sure that B <= C <= D <= n or B >= C >= D >= n
inline pixel_type_w SmoothTendency(pixel_type_w B, pixel_type_w a,
pixel_type_w n) {
pixel_type_w diff = 0;
if (B >= a && a >= n) {
diff = (4 * B - 3 * n - a + 6) / 12;
// 2C = a<<1 + diff - diff&1 <= 2B so diff - diff&1 <= 2B - 2a
// 2D = a<<1 - diff - diff&1 >= 2n so diff + diff&1 <= 2a - 2n
if (diff - (diff & 1) > 2 * (B - a)) diff = 2 * (B - a) + 1;
if (diff + (diff & 1) > 2 * (a - n)) diff = 2 * (a - n);
} else if (B <= a && a <= n) {
diff = (4 * B - 3 * n - a - 6) / 12;
// 2C = a<<1 + diff + diff&1 >= 2B so diff + diff&1 >= 2B - 2a
// 2D = a<<1 - diff + diff&1 <= 2n so diff - diff&1 >= 2a - 2n
if (diff + (diff & 1) < 2 * (B - a)) diff = 2 * (B - a) - 1;
if (diff - (diff & 1) < 2 * (a - n)) diff = 2 * (a - n);
}
return diff;
}
void DefaultSqueezeParameters(std::vector<SqueezeParams> *parameters,
const Image &image);
Status CheckMetaSqueezeParams(const SqueezeParams ¶meter, int num_channels);
Status MetaSqueeze(Image &image, std::vector<SqueezeParams> *parameters);
Status InvSqueeze(Image &input, const std::vector<SqueezeParams> ¶meters,
ThreadPool *pool);
} // namespace jxl
#endif // LIB_JXL_MODULAR_TRANSFORM_SQUEEZE_H_
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