new: add write_png

src/write_png.c

@@ -0,0 +1,82 @@
+#include "write_png.h"
+
+static inline double linear_to_srgb(double x){
+  if (x <= 0.0) return 0.0;
+  if (x >= 1.0) return 1.0;
+  if (x <= 0.0031308) return 12.92 * x;
+  return 1.055 * pow(x, 1.0/2.4) - 0.055;
+}
+
+int buffer_normalize_srgb(double **buffer, int W, int H) {
+  double max = 0;
+  for (int j = 0; j < H; j++) {
+    for (int i = 0; i < W; i++) {
+      for (int c = 0; c < 3; c++) {
+        if (max < buffer[j*W + i][c]) max = buffer[j*W + i][c];
+      }
+    }
+  }
+  if (max == 0) return 1;
+  for (int j = 0; j < H; j++) {
+    for (int i = 0; i < W; i++) {
+      for (int c = 0; c < 3; c++) {
+        buffer[j*W + i][c] /= max;
+        buffer[j*W+i][c] = linear_to_srgb(buffer[j*W+i][c]);
+      }
+    }
+  }
+  return 0;
+}
+
+int write_png(char *filename, double **buffer, int W, int H) {
+  buffer_normalize_srgb(buffer, W, H);
+  size_t bufsize = W*H*3;
+  uint8_t *img = (uint8_t *)malloc(bufsize);
+  if (!img) {return 1;}
+
+  for (int j = 0; j < H; j++) {
+    for (int i = 0; i < W; i++) {
+      for (int c = 0; c < 3; c++) {
+        int v = (int)lrint(buffer[j*W*i][c]);
+        if (v < 0) v = 0;
+        if (v > 255) v = 255;
+        img[j*W*3+i*3+c] = (uint8_t) v;
+      }
+    }
+  }
+
+  int flag = 0;
+  spng_ctx *ctx = spng_ctx_new(SPNG_CTX_ENCODER);
+  if(!ctx){ fprintf(stderr, "spng_ctx_new failed\n"); free(img); return 1; }
+
+  FILE *f = fopen(filename, "wb");
+  if(!f){ fprintf(stderr, "fopen failed\n"); spng_ctx_free(ctx); free(img); return 1; }
+  spng_set_png_file(ctx, f);
+
+  struct spng_ihdr ihdr = {0};
+  ihdr.width = W;
+  ihdr.height = H;
+  ihdr.bit_depth = 8;
+  ihdr.color_type = SPNG_COLOR_TYPE_TRUECOLOR; // RGB
+  ihdr.interlace_method = SPNG_INTERLACE_NONE;
+  ihdr.compression_method = 0;
+  ihdr.filter_method = 0;
+  if( (flag= spng_set_ihdr(ctx, &ihdr)) ){
+    fprintf(stderr, "spng_set_ihdr: %s\n", spng_strerror(flag));
+    fclose(f); spng_ctx_free(ctx); free(img); return 1;
+  }
+
+  #ifndef SPNG_SRGB_INTENT_PERCEPTUAL
+  #define SPNG_SRGB_INTENT_PERCEPTUAL 0
+  #endif
+  spng_set_srgb(ctx, SPNG_SRGB_INTENT_PERCEPTUAL);
+
+  flag = spng_encode_image(ctx, img, bufsize, SPNG_FMT_PNG, SPNG_ENCODE_FINALIZE);
+  if(flag){
+    fprintf(stderr, "spng_encode_image: %s\n", spng_strerror(flag));
+  }
+  fclose(f);
+  spng_ctx_free(ctx);
+  free(img);
+  return flag? 1 : 0;
+}

src/write_png.h

@@ -0,0 +1,6 @@
+#include <spng.h>
+#include <math.h>
+#include <stdint.h>
+
+
+int write_png(char *filename, double **buffer, int W, int H);