使用BitmapSource，PngBitmapEncoder / Decoder时，在PNG中保存8位索引数据会改变原始字节

I have a problem when saving and loading a PNG using BitmapSource and PngBitmapEncoder/Decoder. Basically, I'd like to be able to save an image that originated as an array of bytes, and when the PNG is loaded into my program, reload the exact same bytes. Original data preservation is important.I have a problem when saving and loading a PNG