It can. BMPは基本的に小さなヘッダを持つ未圧縮のRGB列であり、完全に損失なしで、巨大である。. That decides whether the crop is a pure pixel operation or whether the file has to be rebuilt around it.
透明度の決定は，透明度の変更を行う段階である。 That is the step most people actually came for, and doing it after BMP を切り取り rather than before it means the conversion works from the file you finally settled on.
