# Last edited on 2025-08-18 22:09:57 by stolfi

def write_image_via_PNM(rfile, R):
  # Expects {R} to be an RGB image with values in {[0_1]}.
  # Writes it out to file "{rfile}".
  #
  # The image should be a {numpy} array with shape {(ny,nx,nc)}
  # where {nc} is either 1 or 3.
  # 
  ny, nx, nc = numpy.shape(R)
  assert nc == 1 or nc == 3, "bug {nc}"
  ext = "pgm" if nc == 1 else "ppm" # File name extension.
  magic = "P2" if nc == 1 else "P3" # Magic code for PGM or PPM file.
  inSpace = "linearGray" if nc == 1 else "linearRGB"
  outSpace = "Gray" if nc == 1 else "sRGB"
  tfile = f"/tmp/{os.getpid()}-R.{ext}"
  # Write an ascii PGM or PPM:
  maxval = 1023
  with open(tfile, "w") as wr:
    wr.write(f"{magic}\n")
    wr.write(f"{nx} {ny}\n")
    wr.write(f"{maxval}\n")
    for iy in range(ny):
      for ix in range(nx):
        if ix % 20 == 0: wr.write("\n")
        for ic in range(nc):
          fsmp = R[iy,ix,ic]
          ival = int(floor(maxval*fsmp + 0.5))
          if ival < 0 or ival > maxval: prog_error("int sample out of bounds")
          wr.write(f" {ival}")
      wr.write("\n")
    wr.close()
  
  # Convert to PNG:
  bash\
    ( f"convert {tfile}" + \
      f"    -set colorspace {inSpace}" + \
      f"    -depth 8" + \
      f"    -colorspace {outSpace}" +
      f"  {rfile}"
    )
  return
  # ----------------------------------------------------------------------