Differential D25318 Diff 69974 kstars/fitsviewer/stretch.cpp

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kstars/fitsviewer/stretch.cpp

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1​#include "stretch.h"
2​
3​/* Stretch
4​
5​ This application is free software; you can redistribute it and/or
6​ modify it under the terms of the GNU General Public
7​ License as published by the Free Software Foundation; either
8​ version 2 of the License, or (at your option) any later version.
9​*/
10​
11​#include "stretch.h"
12​
13​#include <fitsio.h>
14​#include <math.h>
15​#include <QtConcurrent>
16​
17​namespace {
18​
19​// Returns the median v of the vector.
20​// The vector is modified in an undefined way.
21​template <typename T>
22​T median(std::vector<T>& values)
23​{
24​ const int middle = values.size() / 2;
25​ std::nth_element(values.begin(), values.begin() + middle, values.end());
26​ return values[middle];
27​}
28​
29​// Returns the median of the sample values.
30​// The values are not modified.
31​template <typename T>
32​T median(T *values, int size, int sampleBy)
33​{
34​ const int downsampled_size = size / sampleBy;
35​ std::vector<T> samples(downsampled_size);
36​ for (int index = 0, i = 0; index < size; ++i, index += sampleBy)
37​ samples[i] = values[index];
38​ return median(samples);
39​}
40​
41​// This stretches one channel given the input parameters.
42​// Based on the spec in section 8.5.6
43​// http://pixinsight.com/doc/docs/XISF-1.0-spec/XISF-1.0-spec.html
44​// Uses multiple threads, blocks until done.
45​// The extension parameters are not used.
46​template <typename T>
47​void stretchOneChannel(T *input_buffer, QImage *output_image,
48​ const StretchParams& stretch_params,
49​ int input_range, int image_height, int image_width)
50​{
51​ QVector<QFuture<void>> futures;
52​
53​ // We're outputting uint8, so the max output is 255.
54​ constexpr int maxOutput = 255;
55​
56​ // Maximum possible input value (e.g. 1024*64 - 1 for a 16 bit unsigned int).
57​ const float maxInput = input_range > 1 ? input_range - 1 : input_range;
58​
59​ const float midtones = stretch_params.grey_red.midtones;
60​ const float highlights = stretch_params.grey_red.highlights;
61​ const float shadows = stretch_params.grey_red.shadows;
62​
63​ // Precomputed expressions moved out of the loop.
64​ // hightlights - shadows, protecting for divide-by-0, in a 0->1.0 scale.
65​ const float hsRangeFactor = highlights == shadows ? 1.0 : 1.0 / (highlights - shadows);
66​ // Shadow and highlight values translated to the ADU scale.
67​ const T nativeShadows = shadows * maxInput;
68​ const T nativeHighlights = highlights * maxInput;
69​ // Constants based on above needed for the stretch calculations.
70​ const float k1 = (midtones - 1) * hsRangeFactor * maxOutput / maxInput;
71​ const float k2 = ((2 * midtones) - 1) * hsRangeFactor / maxInput;
72​
73​ for (int j = 0; j < image_height; j++)
74​ {
75​ futures.append(QtConcurrent::run([ = ]()
76​ {
77​ T * inputLine = input_buffer + j * image_width;
78​ auto * scanLine = output_image->scanLine(j);
79​
80​ for (int i = 0; i < image_width; i++)
81​ {
82​ const T input = inputLine[i];
83​ if (input < nativeShadows) scanLine[i] = 0;
84​ else if (input >= nativeHighlights) scanLine[i] = maxOutput;
85​ else
86​ {
87​ const T inputFloored = (input - nativeShadows);
88​ scanLine[i] = (inputFloored * k1) / (inputFloored * k2 - midtones);
89​ }
90​ }
91​ }));
92​ }
93​ for(QFuture<void> future : futures)
94​ future.waitForFinished();
95​}
96​
97​// This is like the above 1-channel stretch, but extended for 3 channels.
98​// This could have been more modular, but the three channels are combined
99​// into a single qRgb value at the end, so it seems the simplest thing is to
100​// replicate the code. It is assume the colors are not interleaved--the red image
101​// is stored fully, then the green, then the blue.
102​template <typename T>
103​void stretchThreeChannels(T *inputBuffer, QImage *outputImage,
104​ const StretchParams& stretchParams,
105​ int inputRange, int imageHeight, int imageWidth)
106​{
107​ QVector<QFuture<void>> futures;
108​
109​ // We're outputting uint8, so the max output is 255.
110​ constexpr int maxOutput = 255;
111​
112​ // Maximum possible input value (e.g. 1024*64 - 1 for a 16 bit unsigned int).
113​ const float maxInput = inputRange > 1 ? inputRange - 1 : inputRange;
114​
115​ const float midtonesR = stretchParams.grey_red.midtones;
116​ const float highlightsR = stretchParams.grey_red.highlights;
117​ const float shadowsR = stretchParams.grey_red.shadows;
118​ const float midtonesG = stretchParams.green.midtones;
119​ const float highlightsG = stretchParams.green.highlights;
120​ const float shadowsG = stretchParams.green.shadows;
121​ const float midtonesB = stretchParams.blue.midtones;
122​ const float highlightsB = stretchParams.blue.highlights;
123​ const float shadowsB = stretchParams.blue.shadows;
124​
125​ // Precomputed expressions moved out of the loop.
126​ // hightlights - shadows, protecting for divide-by-0, in a 0->1.0 scale.
127​ const float hsRangeFactorR = highlightsR == shadowsR ? 1.0 : 1.0 / (highlightsR - shadowsR);
128​ const float hsRangeFactorG = highlightsG == shadowsG ? 1.0 : 1.0 / (highlightsG - shadowsG);
129​ const float hsRangeFactorB = highlightsB == shadowsB ? 1.0 : 1.0 / (highlightsB - shadowsB);
130​ // Shadow and highlight values translated to the ADU scale.
131​ const T nativeShadowsR = shadowsR * maxInput;
132​ const T nativeShadowsG = shadowsG * maxInput;
133​ const T nativeShadowsB = shadowsB * maxInput;
134​ const T nativeHighlightsR = highlightsR * maxInput;
135​ const T nativeHighlightsG = highlightsG * maxInput;
136​ const T nativeHighlightsB = highlightsB * maxInput;
137​ // Constants based on above needed for the stretch calculations.
138​ const float k1R = (midtonesR - 1) * hsRangeFactorR * maxOutput / maxInput;
139​ const float k1G = (midtonesG - 1) * hsRangeFactorG * maxOutput / maxInput;
140​ const float k1B = (midtonesB - 1) * hsRangeFactorB * maxOutput / maxInput;
141​ const float k2R = ((2 * midtonesR) - 1) * hsRangeFactorR / maxInput;
142​ const float k2G = ((2 * midtonesG) - 1) * hsRangeFactorG / maxInput;
143​ const float k2B = ((2 * midtonesB) - 1) * hsRangeFactorB / maxInput;
144​
145​ const int size = imageWidth * imageHeight;
146​
147​ for (int j = 0; j < imageHeight; j++)
148​ {
149​ futures.append(QtConcurrent::run([ = ]()
150​ {
151​ // R, G, B input images are stored one after another.
152​ T * inputLineR = inputBuffer + j * imageWidth;
153​ T * inputLineG = inputLineR + size;
154​ T * inputLineB = inputLineG + size;
155​
156​ auto * scanLine = reinterpret_cast<QRgb*>(outputImage->scanLine(j));
157​
158​ for (int i = 0; i < imageWidth; i++)
159​ {
160​ const T inputR = inputLineR[i];
161​ const T inputG = inputLineG[i];
162​ const T inputB = inputLineB[i];
163​
164​ uint8_t red, green, blue;
165​
166​ if (inputR < nativeShadowsR) red = 0;
167​ else if (inputR >= nativeHighlightsR) red = maxOutput;
168​ else
169​ {
170​ const T inputFloored = (inputR - nativeShadowsR);
171​ red = (inputFloored * k1R) / (inputFloored * k2R - midtonesR);
172​ }
173​
174​ if (inputG < nativeShadowsG) green = 0;
175​ else if (inputG >= nativeHighlightsG) green = maxOutput;
176​ else
177​ {
178​ const T inputFloored = (inputG - nativeShadowsG);
179​ green = (inputFloored * k1G) / (inputFloored * k2G - midtonesG);
180​ }
181​
182​ if (inputB < nativeShadowsB) blue = 0;
183​ else if (inputB >= nativeHighlightsB) blue = maxOutput;
184​ else
185​ {
186​ const T inputFloored = (inputB - nativeShadowsB);
187​ blue = (inputFloored * k1B) / (inputFloored * k2B - midtonesB);
188​ }
189​ scanLine[i] = qRgb(red, green, blue);
190​ }
191​ }));
192​ }
193​ for(QFuture<void> future : futures)
194​ future.waitForFinished();
195​}
196​
197​template <typename T>
198​void stretchChannels(T *input_buffer, QImage *output_image,
199​ const StretchParams& stretch_params,
200​ int input_range, int image_height, int image_width, int num_channels)
201​{
202​ if (num_channels == 1)
203​ stretchOneChannel(input_buffer, output_image, stretch_params, input_range,
204​ image_height, image_width);
205​ else if (num_channels == 3)
206​ stretchThreeChannels(input_buffer, output_image, stretch_params, input_range,
207​ image_height, image_width);
208​}
209​
210​// See section 8.5.7 in above link http://pixinsight.com/doc/docs/XISF-1.0-spec/XISF-1.0-spec.html
211​template <typename T>
212​void computeParamsOneChannel(T *buffer, StretchParams1Channel *params,
213​ int inputRange, int height, int width)
214​{
215​ // Find the median sample.
216​ constexpr int maxSamples = 500000;
217​ const int sampleBy = width * height < maxSamples ? 1 : width * height / maxSamples;
218​ const int size = width * height;
219​ T medianSample = median(buffer, width * height, sampleBy);
220​
221​ // Find the Median deviation: 1.4826 * median of abs(sample[i] - median).
222​ const int numSamples = width * height / sampleBy;
223​ std::vector<T> deviations(numSamples);
224​ for (int index = 0, i = 0; index < size; ++i, index += sampleBy)
225​ {
226​ if (medianSample > buffer[index])
227​ deviations[i] = medianSample - buffer[index];
228​ else
229​ deviations[i] = buffer[index] - medianSample;
230​ }
231​
232​ // Shift everything to 0 -> 1.0.
233​ const float medDev = median(deviations);
234​ const float normalizedMedian = medianSample / static_cast<float>(inputRange);
235​ const float MADN = 1.4826 * medDev / static_cast<float>(inputRange);
236​
237​ const bool upperHalf = normalizedMedian > 0.5;
238​
239​ const float shadows = (upperHalf || MADN == 0) ? 0.0 :
240​ fmin(1.0, fmax(0.0, (normalizedMedian + -2.8 * MADN)));
241​
242​ const float highlights = (!upperHalf || MADN == 0) ? 1.0 :
243​ fmin(1.0, fmax(0.0, (normalizedMedian - -2.8 * MADN)));
244​
245​ float X, M;
246​ constexpr float B = 0.25;
247​ if (!upperHalf) {
248​ X = normalizedMedian - shadows;
249​ M = B;
250​ } else {
251​ X = B;
252​ M = highlights - normalizedMedian;
253​ }
254​ float midtones;
255​ if (X == 0) midtones = 0;
256​ else if (X == M) midtones = 0.5;
257​ else if (X == 1) midtones = 1.0;
258​ else midtones = ((M - 1) * X) / ((2 * M - 1) * X - M);
259​
260​ // Store the params.
261​ params->shadows = shadows;
262​ params->highlights = highlights;
263​ params->midtones = midtones;
264​ params->shadows_expansion = 0.0;
265​ params->highlights_expansion = 1.0;
266​}
267​
268​// Need to know the possible range of input values.
269​// Using the type of the sample and guessing.
270​// Perhaps we should examine the contents for the file
271​// (e.g. look at maximum value and extrapolate from that).
272​int getRange(int data_type)
273​{
274​ switch (data_type)
275​ {
276​ case TBYTE:
277​ return 256;
278​ break;
279​ case TSHORT:
280​ return 64*1024;
281​ break;
282​ case TUSHORT:
283​ return 64*1024;
284​ break;
285​ case TLONG:
286​ return 64*1024;
287​ break;
288​ case TFLOAT:
289​ return 64*1024;
290​ break;
291​ case TLONGLONG:
292​ return 64*1024;
293​ break;
294​ case TDOUBLE:
295​ return 64*1024;
296​ break;
297​ default:
298​ return 64*1024;
299​ break;
300​ }
301​}
302​
303​} // namespace
304​
305​Stretch::Stretch(int width, int height, int channels, int data_type)
306​{
307​ image_width = width;
308​ image_height = height;
309​ image_channels = channels;
310​ dataType = data_type;
311​ input_range = getRange(dataType);
312​}
313​
314​void Stretch::run(uint8_t *input, QImage *outputImage)
315​{
316​ switch (dataType)
317​ {
318​ case TBYTE:
319​ stretchChannels(reinterpret_cast<uint8_t*>(input), outputImage, params,
320​ input_range, image_height, image_width, image_channels);
321​ break;
322​ case TSHORT:
323​ stretchChannels(reinterpret_cast<short*>(input), outputImage, params,
324​ input_range, image_height, image_width, image_channels);
325​ break;
326​ case TUSHORT:
327​ stretchChannels(reinterpret_cast<unsigned short*>(input), outputImage, params,
328​ input_range, image_height, image_width, image_channels);
329​ break;
330​ case TLONG:
331​ stretchChannels(reinterpret_cast<long*>(input), outputImage, params,
332​ input_range, image_height, image_width, image_channels);
333​ break;
334​ case TFLOAT:
335​ stretchChannels(reinterpret_cast<float*>(input), outputImage, params,
336​ input_range, image_height, image_width, image_channels);
337​ break;
338​ case TLONGLONG:
339​ stretchChannels(reinterpret_cast<long long*>(input), outputImage, params,
340​ input_range, image_height, image_width, image_channels);
341​ break;
342​ case TDOUBLE:
343​ stretchChannels(reinterpret_cast<double*>(input), outputImage, params,
344​ input_range, image_height, image_width, image_channels);
345​ break;
346​ default:
347​ break;
348​ }
349​}
350​
351​StretchParams Stretch::computeParams(uint8_t *input)
352​{
353​ StretchParams result;
354​ for (int channel = 0; channel < image_channels; ++channel)
355​ {
356​ int offset = channel * image_width * image_height;
357​ StretchParams1Channel *params = channel == 0 ? &result.grey_red :
358​ (channel == 1 ? &result.green : &result.blue);
359​ switch (dataType)
360​ {
361​ case TBYTE:
362​ {
363​ auto buffer = reinterpret_cast<uint8_t*>(input);
364​ computeParamsOneChannel(buffer + offset, params, input_range,
365​ image_height, image_width);
366​ break;
367​ }
368​ case TSHORT:
369​ {
370​ auto buffer = reinterpret_cast<short*>(input);
371​ computeParamsOneChannel(buffer + offset, params, input_range,
372​ image_height, image_width);
373​ break;
374​ }
375​ case TUSHORT:
376​ {
377​ auto buffer = reinterpret_cast<unsigned short*>(input);
378​ computeParamsOneChannel(buffer + offset, params, input_range,
379​ image_height, image_width);
380​ break;
381​ }
382​ case TLONG:
383​ {
384​ auto buffer = reinterpret_cast<long*>(input);
385​ computeParamsOneChannel(buffer + offset, params, input_range,
386​ image_height, image_width);
387​ break;
388​ }
389​ case TFLOAT:
390​ {
391​ auto buffer = reinterpret_cast<float*>(input);
392​ computeParamsOneChannel(buffer + offset, params, input_range,
393​ image_height, image_width);
394​ break;
395​ }
396​ case TLONGLONG:
397​ {
398​ auto buffer = reinterpret_cast<long long*>(input);
399​ computeParamsOneChannel(buffer + offset, params, input_range,
400​ image_height, image_width);
401​ break;
402​ }
403​ case TDOUBLE:
404​ {
405​ auto buffer = reinterpret_cast<double*>(input);
406​ computeParamsOneChannel(buffer + offset, params, input_range,
407​ image_height, image_width);
408​ break;
409​ }
410​ default:
411​ break;
412​ }
413​ }
414​ return result;
415​}