forked from mtcontrib/leaftest
Add ssim perceptual downscaling
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www/tiles/
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www/tiles-*
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www/conf.json
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downscaling/perc
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downscaling/compile.sh
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downscaling/compile.sh
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gcc -Wall -Ofast -march=native percept_down.c -o perc -lpng -lm
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downscaling/percept_down.c
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downscaling/percept_down.c
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// this is two times as fast when compiled with -Ofast
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// for not tileable textures
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// see https://graphics.ethz.ch/~cengizo/Files/Sig15PerceptualDownscaling.pdf
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#include <stdlib.h> // malloc, EXIT_*
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#include <string.h> // memset
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#include <math.h>
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#include <png.h>
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#define SQR_NP 2 // squareroot of the patch size, recommended: 2
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#define EXIT_PNG(F) if (!F) { \
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fprintf(stderr, "%s\n", bild.message); \
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return EXIT_FAILURE; \
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}
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#define CLAMP(V, A, B) (V) < (A) ? (A) : (V) > (B) ? (B) : (V)
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#define u8 unsigned char
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struct pixel {
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u8 r;
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u8 g;
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u8 b;
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u8 a;
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};
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#define PIXELBYTES 4
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struct matrix {
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int w;
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int h;
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float *data;
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};
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struct image {
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int w;
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int h;
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struct pixel *pixels;
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};
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/*! \brief get y, cb and cr values each in [0;1] from u8 r, g and b values
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*
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* there's gamma correction,
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* see http://www.ericbrasseur.org/gamma.html?i=1#Assume_a_gamma_of_2.2
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* 0.5 is added to cb and cr to have them in [0;1]
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*/
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static void rgb2ycbcr(u8 or, u8 og, u8 ob, float *y, float *cb, float *cr)
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{
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float divider = 1.0f / 255.0f;
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float r = powf(or * divider, 2.2f);
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float g = powf(og * divider, 2.2f);
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float b = powf(ob * divider, 2.2f);
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*y = (0.299f * r + 0.587f * g + 0.114f * b);
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*cb = (-0.168736f * r - 0.331264f * g + 0.5f * b) + 0.5f;
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*cr = (0.5f * r - 0.418688f * g - 0.081312f * b) + 0.5f;
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}
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/*! \brief the inverse of the function above
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*
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* numbers from http://www.equasys.de/colorconversion.html
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* if values are too big or small, they're clamped
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*/
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static void ycbcr2rgb(float y, float cb, float cr, u8 *r, u8 *g, u8 *b)
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{
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float vr = (y + 1.402f * (cr - 0.5f));
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float vg = (y - 0.344136f * (cb - 0.5f) - 0.714136f * (cr - 0.5f));
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float vb = (y + 1.772f * (cb - 0.5f));
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float exponent = 1.0f / 2.2f;
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vr = powf(vr, exponent);
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vg = powf(vg, exponent);
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vb = powf(vb, exponent);
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*r = CLAMP(vr * 255.0f, 0, 255);
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*g = CLAMP(vg * 255.0f, 0, 255);
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*b = CLAMP(vb * 255.0f, 0, 255);
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}
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/*! \brief Convert an rgba image to 4 ycbcr matrices with values in [0, 1]
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*/
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static struct matrix *image_to_matrices(struct image *bild)
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{
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int w = bild->w;
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int h = bild->h;
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struct matrix *matrices = malloc(
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PIXELBYTES * sizeof(struct matrix));
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for (int i = 0; i < PIXELBYTES; ++i) {
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matrices[i].w = w;
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matrices[i].h = h;
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matrices[i].data = malloc(w * h * sizeof(float));
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}
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for (int i = 0; i < w * h; ++i) {
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struct pixel px = bild->pixels[i];
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// put y, cb, cr and transpatency into the matrices
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rgb2ycbcr(px.r, px.g, px.b,
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&matrices[0].data[i], &matrices[1].data[i], &matrices[2].data[i]);
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float divider = 1.0f / 255.0f;
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matrices[3].data[i] = px.a * divider;
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}
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return matrices;
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}
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/*! \brief Convert 4 matrices to an rgba image
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*
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* Note that matrices becomes freed.
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*/
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static struct image *matrices_to_image(struct matrix *matrices)
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{
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struct image *bild = malloc(sizeof(struct image));
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int w = matrices[0].w;
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int h = matrices[0].h;
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bild->w = w;
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bild->h = h;
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struct pixel *pixels = malloc(w * h * PIXELBYTES);
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for (int i = 0; i < w * h; ++i) {
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struct pixel *px = &pixels[i];
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ycbcr2rgb(matrices[0].data[i], matrices[1].data[i], matrices[2].data[i],
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&px->r, &px->g, &px->b);
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float a = matrices[3].data[i] * 255;
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px->a = CLAMP(a, 0, 255);
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}
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for (int i = 0; i < PIXELBYTES; ++i) {
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free(matrices[i].data);
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}
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free(matrices);
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bild->pixels = pixels;
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return bild;
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}
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/*! \brief The actual downscaling algorithm
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*
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* \param mat The 4 matrices obtained form image_to_matrices.
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* \param s The factor by which the image should become downscaled.
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*/
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static void downscale_perc(struct matrix *mat, int s)
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{
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// preparation
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int w = mat->w; // input width
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int h = mat->h;
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float *input = mat->data;
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int w2 = w / s; // output width
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int h2 = h / s;
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int input_size = w * h * sizeof(float);
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int output_size = input_size / (s * s);
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//~ fprintf(stderr, "w, h, s: %d, %d, %d\n", w,h,s);
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float *l = malloc(output_size);
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float *l2 = malloc(output_size);
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float *d = malloc(output_size);
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// set d's entries to 0 (because it's used for a sum)
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for (int i = 0; i < w2 * h2; ++i)
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d[i] = 0;
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// get l and l2, the input image and it's size are used only here
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for (int ysm = 0; ysm < h2; ++ysm) {
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for (int xsm = 0; xsm < w2; ++xsm) {
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// xsm and ysm are coords for the subsampled image
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int x = xsm * s;
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int y = ysm * s;
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float acc = 0;
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float acc2 = 0;
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for (int yc = y; yc < y + s; ++yc) {
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for (int xc = x; xc < x + s; ++xc) {
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// if xc or yc is out of the image, set it to the border
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int y_cl = CLAMP(yc, 0, h-1);
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int x_cl = CLAMP(xc, 0, w-1);
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float v = input[y_cl * w + x_cl];
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acc += v;
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acc2 += v * v;
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}
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}
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int ism = ysm*w2+xsm;
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float divider = 1.0f / (s * s);
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l[ism] = acc * divider;
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l2[ism] = acc2 * divider;
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}
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}
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float patch_sz_div = 1.0f / (SQR_NP * SQR_NP);
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// calculate the average of the results of all possible patch sets
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for (int y_offset = 0; y_offset > -SQR_NP; --y_offset) {
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for (int x_offset = 0; x_offset > -SQR_NP; --x_offset) {
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float *m = malloc(output_size);
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float *r = malloc(output_size);
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// get m
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for (int y = 0; y < h2; ++y) {
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for (int x = 0; x < w2; ++x) {
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float acc = 0;
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int ys = y - (y + SQR_NP + y_offset) % SQR_NP;
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int xs = x - (x + SQR_NP + x_offset) % SQR_NP;
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for (int yc = ys; yc < ys + SQR_NP; ++yc) {
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for (int xc = xs; xc < xs + SQR_NP; ++xc) {
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int y_cl = CLAMP(yc, 0, h2-1);
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int x_cl = CLAMP(xc, 0, w2-1);
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int i = y_cl * w2 + x_cl;
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acc += l[i];
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}
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}
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m[y*w2+x] = acc * patch_sz_div;
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}
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}
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// get r
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for (int y = 0; y < h2; ++y) {
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for (int x = 0; x < w2; ++x) {
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float acc = 0;
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float acc2 = 0;
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int ys = y - (y + SQR_NP + y_offset) % SQR_NP;
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int xs = x - (x + SQR_NP + x_offset) % SQR_NP;
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for (int yc = ys; yc < ys + SQR_NP; ++yc) {
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for (int xc = xs; xc < xs + SQR_NP; ++xc) {
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int y_cl = CLAMP(yc, 0, h2-1);
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int x_cl = CLAMP(xc, 0, w2-1);
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int i = y_cl * w2 + x_cl;
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acc += l[i] * l[i];
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acc2 += l2[i];
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}
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}
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int i = y*w2+x;
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float mv = m[i];
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float slv = acc * patch_sz_div - mv * mv;
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float shv = acc2 * patch_sz_div - mv * mv;
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if (slv >= 0.000001f) // epsilon is 10⁻⁶
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r[i] = sqrtf(shv / slv);
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else
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r[i] = 0;
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}
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}
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// get d, which is the output
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for (int y = 0; y < h2; ++y) {
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for (int x = 0; x < w2; ++x) {
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float acc_m = 0;
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float acc_r = 0;
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float acc_t = 0;
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int ys = y - (y + SQR_NP + y_offset) % SQR_NP;
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int xs = x - (x + SQR_NP + x_offset) % SQR_NP;
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for (int yc = ys; yc < ys + SQR_NP; ++yc) {
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for (int xc = xs; xc < xs + SQR_NP; ++xc) {
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int y_cl = CLAMP(yc, 0, h2-1);
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int x_cl = CLAMP(xc, 0, w2-1);
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int i = y_cl * w2 + x_cl;
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acc_m += m[i];
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acc_r += r[i];
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acc_t += r[i] * m[i];
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}
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}
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int i = y*w2+x;
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d[i] += (
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acc_m * patch_sz_div
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+ acc_r * patch_sz_div * l[i]
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- acc_t * patch_sz_div
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);
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}
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}
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free(m);
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free(r);
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}
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}
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// divide values in d for the (arithmetic) average
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for (int i = 0; i < w2 * h2; ++i)
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d[i] *= patch_sz_div;
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// update the matrix
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mat->data = d;
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mat->w = w2;
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mat->h = h2;
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// tidy up
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free(input);
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free(l);
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free(l2);
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}
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/*! \brief Function which calls functions for downscaling
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*
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* \param bild The image, it's content is changed when finished.
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* \param downscale_factor Must be a natural number.
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*/
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void downscale_an_image(struct image **bild, int downscale_factor)
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{
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struct matrix *matrices = image_to_matrices(*bild);
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for (int i = 0; i < PIXELBYTES; ++i) {
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downscale_perc(&(matrices[i]), downscale_factor);
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}
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*bild = matrices_to_image(matrices);
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}
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int main(int argc, char **args)
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{
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if (argc != 2) {
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fprintf(stderr, "Missing arguments, usage: ./perc <downscaling_factor>"
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"\n");
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return EXIT_FAILURE;
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}
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int downscaling_factor = atoi(args[1]);
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if (downscaling_factor < 2) {
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fprintf(stderr, "Invalid downscaling factor: %d\n",
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downscaling_factor);
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return EXIT_FAILURE;
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}
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png_image bild;
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memset(&bild, 0, sizeof(bild));
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bild.version = PNG_IMAGE_VERSION;
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EXIT_PNG(png_image_begin_read_from_stdio(&bild, stdin))
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int w = bild.width;
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int h = bild.height;
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bild.flags = PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB;
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bild.format = PNG_FORMAT_RGBA;
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struct pixel *pixels = malloc(w * h * 4);
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EXIT_PNG(png_image_finish_read(&bild, NULL, pixels, 0, NULL))
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struct image origpic = {w = w, h = h, pixels = pixels};
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struct image *newpic = &origpic;
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downscale_an_image(&newpic, downscaling_factor);
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bild.width = newpic->w;
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bild.height = newpic->h;
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free(pixels);
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pixels = newpic->pixels;
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free(newpic);
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EXIT_PNG(png_image_write_to_stdio(&bild, stdout, 0, pixels, 0, NULL));
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free(pixels); // redundant free to feed valgrind
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return EXIT_SUCCESS;
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}
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