public void overwriteTRNS(byte r, byte g, byte b) {
                if(hasAlphaChannel()) {
                        throw new UnsupportedOperationException("image has an alpha channel");
                }
                byte[] pal = this.palette;
                if(pal == null) {
                        transPixel = new byte[] { 0, r, 0, g, 0, b };
                } else {
                        paletteA = new byte[pal.length / 3];
                        for(int i = 0, j = 0; i < pal.length; i += 3, j++) {
                                if(pal[i] != r || pal[i + 1] != g || pal[i + 2] != b) {
                                        paletteA[j] = (byte)0xFF;
                                }
                        }
                }
        }