/* ============================================================ * * This file is a part of digiKam project * http://www.digikam.org * * Date : 2005-05-25 * Description : Noise Reduction threaded image filter. * * Copyright (C) 2005-2007 by Gilles Caulier * * Original Noise Filter algorithm copyright (C) 2005 * Peter Heckert * from dcamnoise2 gimp plugin available at this url : * http://home.arcor.de/peter.heckert/dcamnoise2-0.63.c * * This program is free software; you can redistribute it * and/or modify it under the terms of the GNU General * Public License as published by the Free Software Foundation; * either version 2, or (at your option) * any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * ============================================================ */ #ifndef NOISE_REDUCTION_H #define NOISE_REDUCTION_H // C++ includes. #include // Digikam includes. #include "dimgthreadedfilter.h" /**============= NOTICE TO USE THE FILTER =============================================================== * * Let me explain, how the filter works, some understanding is necessary to use it: * * Hint for the novice user: * In most cases only Filter Max Radius, Filter treshold and Texture Detail are needed and the other * params can be left at their default setting. * * Main Filter (Preprocessing) * First, a filtered template is generated, using an adaptive filter. * To see this template, we must set _Luminance tolerance, _Color tolerance to 1.0. *------------------------------------------------------------------------------------------------------------ * * "Filter max. Radius" is preset to 5.0 * This is good for most noise situations. * In any case it must be about the same size as noise granularity ore somewhat more. * If it is set higher than necessary, then it can cause unwanted blur. *------------------------------------------------------------------------------------------------------------ * * "Filter Threshold" should be set so that edges are clearly visible and noise is smoothed out. * This threshold value is not bound to any intensity value, it is bound to the second derivative of * intensity values. * Simply adjust it and watch the preview. Adjustment must be made carefully, because the gap * between "noisy", "smooth", and "blur" is very small. Adjust it as carefully as you would adjust * the focus of a camera. *------------------------------------------------------------------------------------------------------------ * * "Lookahead" defines the pixel distance in which the filter looks ahead for luminance variations * Normally the default value should do. * When _Lookahead is increased, then spikenoise is erased. * Eventually readjust Filter treshold, when you changed lookahead. * When the value is to high, then the adaptive filter cannot longer accurately track image details, and * noise can reappear or blur can occur. * * Minimum value is 1.0, this gives best accuracy when blurring very weak noise. * * I never had good success with other values than 2.0. * However, for images with extemely high or low resolution another value possibly is better. * Use it only as a last ressort. *------------------------------------------------------------------------------------------------------------ * * "Phase Jitter Damping" defines how fast the adaptive filter-radius reacts to luminance variations. * I have preset a value, that should do in most cases. * If increased, then edges appear smoother, if too high, then blur may occur. * If at minimum then noise and phase jitter at edges can occur. * It can suppress Spike noise when increased and this is the preferred method to remove spike noise. *------------------------------------------------------------------------------------------------------------ * * "Sharpness" does just what it says, it improves sharpness. It improves the frequency response for the filter. * When it is too strong then not all noise can be removed, or spike noise may appear. * Set it near to maximum, if you want to remove weak noise or JPEG-artifacts, without loosing detail. *------------------------------------------------------------------------------------------------------------ * * "Erosion". The new filter gives better sharpness and this also gives problems * with spike noise. The Erosion param erodes singular spikes and it has a smooth effect to edges, and sharpens * edges by erosion, so noise at edges is eroded. * The effect is dependant from sharpness,phase-jitter damping and lookahead. * Set it to minimum (zero), if you want to remove weak noise or JPEG-artifacts. * When "Erosion" is increased, then also increasing "Phase Jitter Damping" is often useful * * It works nicely. Apart from removing spike noise it has a sharpening and antialiasing effect to edges * (Sharpening occurs by erosion, not by deconvolution) *------------------------------------------------------------------------------------------------------------ * * "Texture Detail" can be used, to get more or less texture accuracy. * When decreased, then noise and texture are blurred out, when increased then texture is * amplified, but also noise will increase. * It has almost no effect to image edges, opposed to Filter theshold, which would blur edges, when increased. * * E.g. if Threshold is adjusted in away so that edges are sharp, and there is still too much area noise, then * Texture detail could be used to reduce noise without blurring edges. * (Another way would be to decrease radius and to increase threshold) * *------------------------------------------------------------------------------------------------------------ * * The filtered image that is now seen in the preview, is used as template for the following processing steps, * therefore it is important to do this adjustment in first place and to do it as good as possible. *------------------------------------------------------------------------------------------------------------ * * Combining original image and filtered image, using tolerance thresholds (Postprocessing) * This can give a final touch of sharpness to your image. * It is not necessary to do this, if you want to reduce JPEG-artifacts or weak noise. * It's purpose is to master strong noise without loosing too much sharpness. * * Note, that this all is done in one filter invocation. Preprocessing and postprocessing is done in one run, * but logically and in the algorithm they are different and ordered processes. * * * Adjust _Color tolerance or/and Luminance tolerance, (if necessary) so that you get the final image. * I recommend to use only one, either _Color or _Luminance. * These settings do not influence the main smoothing process. What they really do is this: * * The tolerance values are used as error-thresholds to compare the filtered template with the original * image. The plugin algorithm uses them to combine the filtered template with the original image * so that noise and filter errors (blur) are thrown out. * A filtered pixel, that is too far away from the original pixel will be overridden by original image content. * * Hint: * If you cange other sliders, like lookahead or Texture Detail, then you should set color tolerance and * luminance tolerance to 1.0 (right end), because otherwise the filtered template is partially hidden * and e.g. the effects for the damping filter cant be seen clearly and cant be optimized. *------------------------------------------------------------------------------------------------------------ * * _Gamma can be used to increase the tolerance values for darker areas (which commonly are more noisy) * This results in more blur for shadow areas. * * Hint for users of previous versions: * Gamma also influences the main-filter process. While the previous version did not have this feature, * I have reimplemented it, however, the algorithm used is totally new. * * * Keep in mind, how the filter works, then usage should be easy! * * * ================ THEORY AND TECHNIC ======================================================================= * * Some interesting things (theoretic and technic) * This plugin bases on the assumption, that noise has no 2-dimensional correlation and therefore * can be removed in a 1-dimensional process. * To remove noise, I use a four-times boxfilter with variable radius. * * The radius is calculated from 2nd derivative of pixeldata. * A gauss filter is used to calculte 2nd derivative. * The filter has some inbuilt features to clip low amplitude noise to clip very high values that would * slow down response time. * The 2nd derivative is lowpassfiltered and then radius is calculated as (Filter Treshold)/2nd_derivative. * The radius modulation data is precalulated and buffered an is used to steer filter radius when * the actual filtering occurs. * * Noise and texture can be further suppressed by nonlinear distortion before adaptive filtering. * To make this possible I subtract low frequency from image data before denoising, so that I get a * bipolar, zerosymmetric image signal. * * The filter works in a /one-dimensional/ way. It is applied to x and then to y axis. * * After filtering a zerodimensional point operator (pixel by pixel comparison) is used, where * filter-errors are thrown out. * This is meant to limit and control filter errors,it can give "final touch" to the image, but it has * nothing to do with the main filter process. * * I do not know if something like this filter already exists. * It is all based on my own ideas and experiments. * Possibly a separable adaptive gauss-filter is a new thing. * Also it is an impossible thing, from a mathemathical point of view ;-) * It is possible only for bandwidth limited images. * Happyly most photographic images are bandwidth limited, or when they are noisy then we want * to limit banwith locally. And this is, what the filter does: It limits bandwidth locally, dependent * from (approximately) 2nd derivative of intensity. * * Because gauss filtering is essentially linear diffusion, and because this filter uses a variable * nonlinear modulated gaussfilter (four box passes are almost gauss) we could say, that this filter * implements a special subclass of nonlinear adaptive diffusion, which is separable, and indeed, * results are very similar to nonlinear diffusion filters. * However, because the filter is separable, it is much faster and needs less memory. */ namespace DigikamNoiseReductionImagesPlugin { class NoiseReduction : public Digikam::DImgThreadedFilter { public: NoiseReduction(Digikam::DImg *orgImage, TQObject *parent, double radius, double lsmooth, double effect, double texture, double sharp, double csmooth, double lookahead, double gamma, double damping, double phase); ~NoiseReduction(){}; private: void filterImage(void); void iir_init(double r); void box_filter(double *src, double *end, double *dest, double radius); void iir_filter(float* const start, float* const end, float* dstart, double radius, const int type); void filter(float *buffer, float *data, float *data2, float *rbuf, float *tbuf, int width, int color); void blur_line(float* const data, float* const data2, float* const buffer, float* rbuf, float* tbuf, const uchar *src, uchar *dest, int len); inline double mypow(double val, double ex) { if (fabs(val) < 1e-16) return 0.0; if (val > 0.0) return exp(log(val)*ex); return -exp(log(-val)*ex); }; private: struct iir_param { double B, b1, b2, b3, b0, r, q; double *p; } m_iir; enum IIRFilteringMode { Gaussian=0, SecondDerivative }; int m_clampMax; double m_radius; double m_lsmooth; double m_csmooth; double m_effect; double m_lookahead; double m_gamma; double m_damping; double m_phase; double m_texture; double m_sharp; }; } // NameSpace DigikamNoiseReductionImagesPlugin #endif /* NOISE_REDUCTION_H */