png.py 文件源码

def write_pnm(file, width, height, pixels, meta):
    """Write a Netpbm PNM/PAM file."""

    bitdepth = meta['bitdepth']
    maxval = 2**bitdepth - 1
    # Rudely, the number of image planes can be used to determine
    # whether we are L (PGM), LA (PAM), RGB (PPM), or RGBA (PAM).
    planes = meta['planes']
    # Can be an assert as long as we assume that pixels and meta came
    # from a PNG file.
    assert planes in (1,2,3,4)
    if planes in (1,3):
        if 1 == planes:
            # PGM
            # Could generate PBM if maxval is 1, but we don't (for one
            # thing, we'd have to convert the data, not just blat it
            # out).
            fmt = 'P5'
        else:
            # PPM
            fmt = 'P6'
        file.write('%s %d %d %d\n' % (fmt, width, height, maxval))
    if planes in (2,4):
        # PAM
        # See http://netpbm.sourceforge.net/doc/pam.html
        if 2 == planes:
            tupltype = 'GRAYSCALE_ALPHA'
        else:
            tupltype = 'RGB_ALPHA'
        file.write('P7\nWIDTH %d\nHEIGHT %d\nDEPTH %d\nMAXVAL %d\n'
                   'TUPLTYPE %s\nENDHDR\n' %
                   (width, height, planes, maxval, tupltype))
    # Values per row
    vpr = planes * width
    # struct format
    fmt = '>%d' % vpr
    if maxval > 0xff:
        fmt = fmt + 'H'
    else:
        fmt = fmt + 'B'
    for row in pixels:
        file.write(struct.pack(fmt, *row))
    file.flush()