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aptdec
mirror of https://github.com/Xerbo/aptdec
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Add realtime decoding 

Change calibration to better suit constant gain
Add -Wextra to Makefile
Add link to model of the PLL
Max number of rows for the image is now increasible
tags/v1.8.0
Xerbo 4 years ago
parent
cd3b206d7a
commit
94dccc74e5
7 changed files with 207 additions and 154 deletions
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  1. +1
    -1
      Makefile
  2. +22
    -3
      README.md
  3. +1
    -2
      dsp.c
  4. +50
    -86
      image.c
  5. +22
    -8
      main.c
  6. +1
    -0
      offsets.h
  7. +110
    -54
      pngio.c

+ 1
- 1
Makefile View File

@@ -1,7 +1,7 @@
CC = gcc
BIN = /usr/bin
INCLUDES = -I.
CFLAGS = -O3 -DNDEBUG -Wall $(INCLUDES)
CFLAGS = -O3 -DNDEBUG -Wall -Wextra $(INCLUDES)
OBJS = main.o image.o dsp.o filter.o reg.o fcolor.o pngio.o median.o color.o

aptdec: $(OBJS)


+ 22
- 3
README.md View File

@@ -51,7 +51,7 @@ To uninstall
## Options

```
-i [r|a|b|c|t|l]
-i [r|a|b|c|t|m]
Output image type
Raw (r), Channel A (a), Channel B (b), False Color (c), Temperature (t) or MCIR (m)
Default: "ab"
@@ -65,7 +65,7 @@ Satellite number
For temperature calibration
Default: "19"

-e [t|h]
-e [t|h|d|p]
Effects
Histogram equalise (h), Crop Telemetry (t), Denoise (d) or Precipitation (p)
Defaults: off
@@ -76,6 +76,9 @@ Map file generated by wxmap
-c <file>
Use configuration file for false color generation
Default: Internal defaults

-r
Realtime decode. When decoding in realtime it is highly recommended to choose a plain raw image.
```

## Output
@@ -97,12 +100,28 @@ Currently there are 4 available effects:
- `d` for a median denoise filter
- `p` for a precipitation overlay

## Example
## Examples

`aptdec -d images -i ab *.wav`

This will process all `.wav` files in the current directory, generate calibrated channel A and B images and put them in the `images` directory.

`aptdec -e dh -i b audio.wav`

Decode `audio.wav` with denoise and histogram equalisation and save it into the current directory.

## Realtime decoding

As of recently a realtime output was added allowing realtime decoding of images.

```
mkfifo /tmp/aptaudio
aptdec /tmp/aptaudio
sox -t pulseaudio alsa_output.pci-0000_00_1b.0.analog-stereo.monitor -c 1 -t wav /tmp/aptaudio
```

Perform a realtime decode with the audio being played out of`alsa_output.pci-0000_00_1b.0.analog`.

## Further reading

[https://noaasis.noaa.gov/NOAASIS/pubs/Users_Guide-Building_Receive_Stations_March_2009.pdf](https://noaasis.noaa.gov/NOAASIS/pubs/Users_Guide-Building_Receive_Stations_March_2009.pdf)


+ 1
- 2
dsp.c View File

@@ -97,9 +97,8 @@ static inline double Phase(double I, double Q) {
}

/* Phase locked loop
* https://en.wikipedia.org/wiki/Phase-locked_loop
* https://arachnoid.com/phase_locked_loop/
* https://simple.wikipedia.org/wiki/Phase-locked_loop
* Model of this filter here https://www.desmos.com/calculator/m0uadgkoee
*/
static double pll(double I, double Q) {
// PLL coefficient


+ 50
- 86
image.c View File

@@ -32,7 +32,7 @@ typedef struct {
} rgparam_t;

typedef struct {
float *prow[3000]; // Row buffers
float *prow[MAX_HEIGHT]; // Row buffers
int nrow; // Number of rows
int chA, chB; // ID of each channel
char name[256]; // Stripped filename
@@ -44,6 +44,7 @@ typedef struct {
int satnum; // The satellite number
char *map; // Path to a map file
char *path; // Output directory
int realtime;
} options_t;

extern void polyreg(const int m, const int n, const double x[], const double y[], double c[]);
@@ -70,7 +71,6 @@ static double rgcal(float x, rgparam_t *rgpr) {

static double tele[16];
static double Cs;
static int nbtele;

void histogramEqualise(float **prow, int nrow, int offset, int width){
// Plot histogram
@@ -101,77 +101,59 @@ void histogramEqualise(float **prow, int nrow, int offset, int width){
}

// Brightness calibrate, including telemetry
void calibrateBrightness(float **prow, int nrow, int offset, int width, int telestart, rgparam_t regr[30]){
void calibrateImage(float **prow, int nrow, int offset, int width, rgparam_t regr){
offset -= SYNC_WIDTH+SPC_WIDTH;

for (int n = 0; n < nrow; n++) {
float *pixelv = prow[n];

for (int i = 0; i < width+SYNC_WIDTH+SPC_WIDTH+TELE_WIDTH; i++) {
float pv = pixelv[i + offset];
float pv = rgcal(pixelv[i + offset], &regr);

// Blend between the calculated regression curves
/* FIXME: this can actually make the image look *worse*
* if the signal has a constant input gain.
*/
/*int k, kof;
k = (n - telestart) / FRAME_LEN;
if (k >= nbtele)
k = nbtele - 1;
kof = (n - telestart) % FRAME_LEN;

if (kof < 64) {
if (k < 1) {*/
pv = rgcal(pv, &(regr[4]));
/*} else {
pv = rgcal(pv, &(regr[k])) * (64 + kof) / FRAME_LEN +
rgcal(pv, &(regr[k - 1])) * (64 - kof) / FRAME_LEN;
}
} else {
if ((k + 1) >= nbtele) {
pv = rgcal(pv, &(regr[k]));
} else {
pv = rgcal(pv, &(regr[k])) * (192 - kof) / FRAME_LEN +
rgcal(pv, &(regr[k + 1])) * (kof - 64) / FRAME_LEN;
}
}
*/
pv = CLIP(pv, 0, 255);
pixelv[i + offset] = pv;
pixelv[i + offset] = CLIP(pv, 0, 255);
}
}
}

double teleNoise(double wedges[16]){
int pattern[9] = { 31, 63, 95, 127, 159, 191, 223, 255, 0 };
double noise = 0;
for(int i = 0; i < 9; i++)
noise += fabs(wedges[i] - (double)pattern[i]);
return noise;
}

// Get telemetry data for thermal calibration/equalization
int calibrate(float **prow, int nrow, int offset, int width) {
double teleline[3000] = { 0.0 };
double teleline[MAX_HEIGHT] = { 0.0 };
double wedge[16];
rgparam_t regr[30];
int n, k;
int mtelestart = 0, telestart;
int channel = -1;
int telestart, mtelestart = 0;
int channel = -1;

// The minimum rows required to decode a full frame
if (nrow < 192) {
fprintf(stderr, ERR_TELE_ROW);
return 0;
}

// Calculate average of a row of telemetry
for (n = 0; n < nrow; n++) {
for (int n = 0; n < nrow; n++) {
float *pixelv = prow[n];

// Average the center 40px
for (int i = 3; i < 43; i++) teleline[n] += pixelv[i + offset + width];
for (int i = 3; i < 43; i++)
teleline[n] += pixelv[i + offset + width];
teleline[n] /= 40.0;
}

// The minimum rows required to decode a full frame
if (nrow < 192) {
fprintf(stderr, ERR_TELE_ROW);
return(0);
}

/* Wedge 7 is white and 8 is black, which will have the largest
/* Wedge 7 is white and 8 is black, this will have the largest
* difference in brightness, this will always be in the center of
* the frame and can thus be used to find the start of the frame
*/
double max = 0.0;
for (n = nrow / 3 - 64; n < 2 * nrow / 3 - 64; n++) {
for (int n = nrow / 3 - 64; n < 2 * nrow / 3 - 64; n++) {
float df;

// (sum 4px below) / (sum 4px above)
@@ -194,68 +176,50 @@ int calibrate(float **prow, int nrow, int offset, int width) {
return(0);
}

// For each frame
for (n = telestart, k = 0; n < nrow - FRAME_LEN; n += FRAME_LEN, k++) {
float *pixelv = prow[n];
int j;
// Find the least noisy frame
double minNoise = -1;
int bestFrame = telestart;
for (int n = telestart, k = 0; n < nrow - FRAME_LEN; n += FRAME_LEN, k++) {
// Turn pixels into wedge values
for (int j = 0; j < 16; j++) {
wedge[j] = 0.0;

// Turn each wedge into a value
for (j = 0; j < 16; j++) {
// Average the middle 6px
wedge[j] = 0.0;
for (int i = 1; i < 7; i++) wedge[j] += teleline[(j * 8) + n + i];
for (int i = 1; i < 7; i++)
wedge[j] += teleline[(j * 8) + i + n];
wedge[j] /= 6;
}

// Compute regression on the wedges
rgcomp(wedge, &(regr[k]));
double noise = teleNoise(wedge);
if(noise < minNoise || minNoise == -1){
minNoise = noise;
bestFrame = k;

// Read the telemetry values from the middle of the image
if (k == nrow / (2*FRAME_LEN)) {
int l;

// Equalise
for (j = 0; j < 16; j++) tele[j] = rgcal(wedge[j], &(regr[k]));
// Compute & apply regression on the wedges
rgcomp(wedge, &regr[k]);
for (int j = 0; j < 16; j++)
tele[j] = rgcal(wedge[j], &regr[k]);

/* Compare the channel ID wedge to the reference
* wedges, the wedge with the closest match will
* be the channel ID
*/
float min = -1;
for (j = 0; j < 6; j++) {
float df;

df = tele[15] - tele[j];
for (int j = 0; j < 6; j++) {
float df = tele[15] - tele[j];
df *= df;

if (df < min || min == -1) {
channel = j;
min = df;
}
}

// Cs computation, still have no idea what this does
int i;
for (Cs = 0.0, i = 0, j = n; j < n + FRAME_LEN; j++) {
double csline;

for (csline = 0.0, l = 3; l < 43; l++)
csline += pixelv[l + offset - SPC_WIDTH];
csline /= 40.0;
if (csline > 50.0) {
Cs += csline;
i++;
}
}
Cs /= i;
Cs = rgcal(Cs, &(regr[k]));
}
}
nbtele = k;

calibrateBrightness(prow, nrow, offset, width, telestart, regr);
calibrateImage(prow, nrow, offset, width, regr[bestFrame]);

return(channel + 1);
return channel + 1;
}

// --- Temperature Calibration --- //


+ 22
- 8
main.c View File

@@ -38,10 +38,11 @@ typedef struct {
int satnum; // The satellite number
char *map; // Path to a map file
char *path; // Output directory
int realtime;
} options_t;

typedef struct {
float *prow[3000]; // Row buffers
float *prow[MAX_HEIGHT]; // Row buffers
int nrow; // Number of rows
int chA, chB; // ID of each channel
char name[256]; // Stripped filename
@@ -55,6 +56,9 @@ extern int init_dsp(double F);
extern int readfcconf(char *file);
extern int readRawImage(char *filename, float **prow, int *nrow);
extern int ImageOut(options_t *opts, image_t *img, int offset, int width, char *desc, char *chid, char *palette);
extern void closeWriter();
extern void pushRow(float *row, int width);
extern int initWriter(options_t *opts, image_t *img, int width, int height, char *desc, char *chid);

// Image functions
extern int calibrate(float **prow, int nrow, int offset, int width);
@@ -90,11 +94,11 @@ int main(int argc, char **argv) {
usage();
}

options_t opts = { "r", "", 19, "", "." };
options_t opts = { "r", "", 19, "", ".", 0 };

// Parse arguments
int opt;
while ((opt = getopt(argc, argv, "c:m:d:i:s:e:")) != EOF) {
while ((opt = getopt(argc, argv, "c:m:d:i:s:e:r")) != EOF) {
switch (opt) {
case 'd':
opts.path = optarg;
@@ -118,6 +122,9 @@ int main(int argc, char **argv) {
case 'e':
opts.effects = optarg;
break;
case 'r':
opts.realtime = 1;
break;
default:
usage();
}
@@ -153,6 +160,8 @@ static int processAudio(char *filename, options_t *opts){
strcpy(path, dirname(path));
sscanf(basename(filename), "%[^.].%s", img.name, extension);

if(opts->realtime) initWriter(opts, &img, IMG_WIDTH, MAX_HEIGHT, "Unprocessed realtime image", "r");

if(strcmp(extension, "png") == 0){
// Read PNG into image buffer
printf("Reading %s", filename);
@@ -166,7 +175,7 @@ static int processAudio(char *filename, options_t *opts){
exit(EPERM);

// Build image
for (img.nrow = 0; img.nrow < 3000; img.nrow++) {
for (img.nrow = 0; img.nrow < MAX_HEIGHT; img.nrow++) {
// Allocate memory for this row
img.prow[img.nrow] = (float *) malloc(sizeof(float) * 2150);
@@ -174,6 +183,8 @@ static int processAudio(char *filename, options_t *opts){
if (getpixelrow(img.prow[img.nrow], img.nrow, &zenith) == 0)
break;

if(opts->realtime) pushRow(img.prow[img.nrow], IMG_WIDTH);

fprintf(stderr, "Row: %d\r", img.nrow);
fflush(stderr);
}
@@ -182,6 +193,8 @@ static int processAudio(char *filename, options_t *opts){
sf_close(audioFile);
}

if(opts->realtime) closeWriter();

printf("\nTotal rows: %d\n", img.nrow);

// Fallback for detecting the zenith
@@ -248,7 +261,7 @@ static int processAudio(char *filename, options_t *opts){
// Channel B
if (CONTAINS(opts->type, 'b')) {
sprintf(desc, "%s (%s)", ch.id[img.chB], ch.name[img.chB]);
ImageOut(opts, &img, CHB_OFFSET, CH_WIDTH, desc, ch.id[img.chA], NULL);
ImageOut(opts, &img, CHB_OFFSET, CH_WIDTH, desc, ch.id[img.chB], NULL);
}

// Distribution image
@@ -292,7 +305,7 @@ static int initsnd(char *filename) {

// Read samples from the wave file
int getsample(float *sample, int nb) {
return sf_read_float(audioFile, sample, nb);
return sf_read_float(audioFile, sample, nb);
}

static void usage(void) {
@@ -304,7 +317,7 @@ static void usage(void) {
" h: Histogram equalise\n"
" d: Denoise\n"
" p: Precipitation\n"
" -i [r|a|b|c|t] Output image\n"
" -i [r|a|b|c|t|m] Output image\n"
" r: Raw\n"
" a: Channel A\n"
" b: Channel B\n"
@@ -314,7 +327,8 @@ static void usage(void) {
" -d <dir> Image destination directory.\n"
" -s [15-19] Satellite number\n"
" -c <file> False color config file\n"
" -m <file> Map file\n");
" -m <file> Map file\n"
" -r Realtime decode");

exit(EINVAL);
}

+ 1
- 0
offsets.h View File

@@ -27,6 +27,7 @@
#define CHA_OFFSET (SYNC_WIDTH+SPC_WIDTH)
#define CHB_OFFSET (SYNC_WIDTH+SPC_WIDTH+CH_WIDTH+TELE_WIDTH+SYNC_WIDTH+SPC_WIDTH)
#define TOTAL_TELE (SYNC_WIDTH+SPC_WIDTH+TELE_WIDTH+SYNC_WIDTH+SPC_WIDTH+TELE_WIDTH)
#define MAX_HEIGHT 3000

#define CLIP(val, bottom, top) (val > top ? top : (val > bottom ? val : bottom))
#define CONTAINS(str, char) (strchr(str, (int) char) != NULL)

+ 110
- 54
pngio.c View File

@@ -30,10 +30,27 @@ typedef struct {
float r, g, b;
} rgb_t;

typedef struct {
float *prow[MAX_HEIGHT]; // Row buffers
int nrow; // Number of rows
int chA, chB; // ID of each channel
char name[256]; // Stripped filename
} image_t;

typedef struct {
char *type; // Output image type
char *effects;
int satnum; // The satellite number
char *map; // Path to a map file
char *path; // Output directory
int realtime;
} options_t;

extern int zenith;
extern char PrecipPalette[256*3];
extern rgb_t applyPalette(char *palette, int val);
extern rgb_t RGBcomposite(rgb_t top, float top_a, rgb_t bottom, float bottom_a);
extern rgb_t falsecolor(float vis, float temp);

int mapOverlay(char *filename, rgb_t **crow, int nrow, int zenith, int MCIR) {
FILE *fp = fopen(filename, "rb");
@@ -118,7 +135,6 @@ int mapOverlay(char *filename, rgb_t **crow, int nrow, int zenith, int MCIR) {

// Map overlay on channel A
crow[y][cha] = RGBcomposite(map, alpha, crow[y][cha], 1);

// Map overlay on channel B
if(!MCIR)
crow[y][chb] = RGBcomposite(map, alpha, crow[y][chb], 1);
@@ -188,33 +204,20 @@ int readRawImage(char *filename, float **prow, int *nrow) {
return 1;
}

typedef struct {
float *prow[3000]; // Row buffers
int nrow; // Number of rows
int chA, chB; // ID of each channel
char name[256]; // Stripped filename
} image_t;
png_text text_ptr[] = {
{PNG_TEXT_COMPRESSION_NONE, "Software", VERSION},
{PNG_TEXT_COMPRESSION_NONE, "Channel", "Unknown", 7},
{PNG_TEXT_COMPRESSION_NONE, "Description", "NOAA satellite image", 20}
};

typedef struct {
char *type; // Output image type
char *effects;
int satnum; // The satellite number
char *map; // Path to a map file
char *path; // Output directory
} options_t;

//int ImageOut(char *filename, char *chid, float **prow, int nrow, int width, int offset, char *palette, char *effects, char *mapFile) {
int ImageOut(options_t *opts, image_t *img, int offset, int width, char *desc, char *chid, char *palette){
char outName[384];
sprintf(outName, "%s/%s-%s.png", opts->path, img->name, chid);
FILE *pngfile;
text_ptr[1].text = desc;
text_ptr[1].text_length = sizeof(desc);

png_text text_ptr[] = {
{PNG_TEXT_COMPRESSION_NONE, "Software", VERSION},
{PNG_TEXT_COMPRESSION_NONE, "Channel", desc, sizeof(desc)},
{PNG_TEXT_COMPRESSION_NONE, "Description", "NOAA satellite image", 20}
};
FILE *pngfile;

// Reduce the width of the image to componsate for the missing telemetry
int fcimage = strcmp(desc, "False Color") == 0;
@@ -229,13 +232,13 @@ int ImageOut(options_t *opts, image_t *img, int offset, int width, char *desc, c
if (!png_ptr) {
png_destroy_write_struct(&png_ptr, (png_infopp) NULL);
fprintf(stderr, ERR_PNG_WRITE);
return(0);
return 0;
}
png_infop info_ptr = png_create_info_struct(png_ptr);
if (!info_ptr) {
png_destroy_write_struct(&png_ptr, (png_infopp) NULL);
fprintf(stderr, ERR_PNG_INFO);
return(0);
return 0;
}

int greyscale = 0;
@@ -254,35 +257,34 @@ int ImageOut(options_t *opts, image_t *img, int offset, int width, char *desc, c
}

png_set_text(png_ptr, info_ptr, text_ptr, 3);

// Channel = 25cm wide
png_set_pHYs(png_ptr, info_ptr, 3636, 3636, PNG_RESOLUTION_METER);

// Init I/O
pngfile = fopen(outName, "wb");
if (!pngfile) {
fprintf(stderr, ERR_FILE_WRITE, outName);
return(1);
return 1;
}
png_init_io(png_ptr, pngfile);
png_write_info(png_ptr, info_ptr);

// Move prow into crow, crow ~ color rows
rgb_t *crow[img->nrow];
for(int y = 0; y < img->nrow; y++){
crow[y] = (rgb_t *) malloc(sizeof(rgb_t) * IMG_WIDTH);
if(!greyscale){
for(int y = 0; y < img->nrow; y++){
crow[y] = (rgb_t *) malloc(sizeof(rgb_t) * IMG_WIDTH);

for(int x = 0; x < IMG_WIDTH; x++){
if(palette == NULL){
crow[y][x].r = crow[y][x].g = crow[y][x].b = CLIP(img->prow[y][x], 0, 255);
}else{
crow[y][x] = applyPalette(palette, img->prow[y][x]);
for(int x = 0; x < IMG_WIDTH; x++){
if(palette == NULL)
crow[y][x].r = crow[y][x].g = crow[y][x].b = CLIP(img->prow[y][x], 0, 255);
else
crow[y][x] = applyPalette(palette, img->prow[y][x]);
}
}
}

// Precipitation
// TODO: use temperature calibration for accuracy
// TODO: use temperature calibration
if(CONTAINS(opts->effects, 'p')){
for(int y = 0; y < img->nrow; y++){
for(int x = 0; x < CH_WIDTH; x++){
@@ -292,6 +294,7 @@ int ImageOut(options_t *opts, image_t *img, int offset, int width, char *desc, c
}
}

// Map stuff
if(opts->map != NULL && opts->map[0] != '\0'){
if(mapOverlay(opts->map, crow, img->nrow, zenith, strcmp(chid, "MCIR") == 0) == 0){
fprintf(stderr, "Skipping MCIR generation; see above.\n");
@@ -304,11 +307,10 @@ int ImageOut(options_t *opts, image_t *img, int offset, int width, char *desc, c

printf("Writing %s", outName);

extern rgb_t falsecolor(float vis, float temp);

// Build image
for (int y = 0; y < img->nrow; y++) {
png_color pix[width];
png_byte gpix[width];
int skip = 0;
for (int x = 0; x < width; x++) {
@@ -320,31 +322,24 @@ int ImageOut(options_t *opts, image_t *img, int offset, int width, char *desc, c
case CH_WIDTH:
skip += TELE_WIDTH + SYNC_WIDTH + SPC_WIDTH;
break;
case CH_WIDTH*2:
skip += TELE_WIDTH;
break;
}
}

if(greyscale){
// Horrific but works
if(x % 3 == 0){
pix[x/3].red = img->prow[y][x + skip + offset ];
pix[x/3].green = img->prow[y][x + skip + offset+1];
pix[x/3].blue = img->prow[y][x + skip + offset+2];
}
gpix[x] = img->prow[y][x + skip + offset];
}else if(fcimage){
rgb_t pixel = falsecolor(img->prow[y][x + CHA_OFFSET], img->prow[y][x + CHB_OFFSET]);
pix[x].red = pixel.r;
pix[x].green = pixel.g;
pix[x].blue = pixel.b;
pix[x] = (png_color){pixel.r, pixel.g, pixel.b};
}else{
pix[x].red = crow[y][x + skip + offset].r;
pix[x].green = crow[y][x + skip + offset].g;
pix[x].blue = crow[y][x + skip + offset].b;
pix[x] = (png_color){crow[y][x + skip + offset].r, crow[y][x + skip + offset].g, crow[y][x + skip + offset].b};
}
}
png_write_row(png_ptr, (png_bytep) pix);
if(greyscale){
png_write_row(png_ptr, (png_bytep) gpix);
}else{
png_write_row(png_ptr, (png_bytep) pix);
}
}

// Tidy up
@@ -353,6 +348,67 @@ int ImageOut(options_t *opts, image_t *img, int offset, int width, char *desc, c
printf("\nDone\n");
png_destroy_write_struct(&png_ptr, &info_ptr);

return(1);
return 1;
}

// TODO: remove these from the global scope
png_structp rt_png_ptr;
png_infop rt_info_ptr;
FILE *rt_pngfile;

int initWriter(options_t *opts, image_t *img, int width, int height, char *desc, char *chid){
char outName[384];
sprintf(outName, "%s/%s-%s.png", opts->path, img->name, chid);

text_ptr[1].text = desc;
text_ptr[1].text_length = sizeof(desc);

// Create writer
rt_png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
if (!rt_png_ptr) {
png_destroy_write_struct(&rt_png_ptr, (png_infopp) NULL);
fprintf(stderr, ERR_PNG_WRITE);
return 0;
}
rt_info_ptr = png_create_info_struct(rt_png_ptr);
if (!rt_info_ptr) {
png_destroy_write_struct(&rt_png_ptr, (png_infopp) NULL);
fprintf(stderr, ERR_PNG_INFO);
return 0;
}

// Greyscale image
png_set_IHDR(rt_png_ptr, rt_info_ptr, width, height,
8, PNG_COLOR_TYPE_GRAY, PNG_INTERLACE_NONE,
PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
png_set_text(rt_png_ptr, rt_info_ptr, text_ptr, 3);

// Channel = 25cm wide
png_set_pHYs(rt_png_ptr, rt_info_ptr, 3636, 3636, PNG_RESOLUTION_METER);

// Init I/O
rt_pngfile = fopen(outName, "wb");
if (!rt_pngfile) {
fprintf(stderr, ERR_FILE_WRITE, outName);
return 0;
}
png_init_io(rt_png_ptr, rt_pngfile);
png_write_info(rt_png_ptr, rt_info_ptr);
return 1;
}

void pushRow(float *row, int width){
png_byte pix[width];
for(int i = 0; i < width; i++)
pix[i] = row[i];
png_write_row(rt_png_ptr, (png_bytep) pix);
}

void closeWriter(){
png_write_end(rt_png_ptr, rt_info_ptr);
fclose(rt_pngfile);
png_destroy_write_struct(&rt_png_ptr, &rt_info_ptr);
}

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