I am no expert in the PNG file format -
Check out the Table in the PNG file format here
Maybe you are getting a IHDR chunk and the PLTE chunk. However as per the table it should be only in the beginning and probably PLTE and IHDR together would be more that 7 bytes.
It might also be some data stream you could ignore maybe.
Or maybe its an older version of PNG file format and needs to be interpreted differently.
In the end you might want to see how libpng deals with it.
Hope this helps.
: We are trying to build a PNG Encoder. We have problems understanding how is the IDAT chunk built. We understand that the first 4 bytes are the length,the second 4 bytes are the IDAT signature, then raw data and of course 4 bytes of CRC at the end. Our problem is that the first 7 bytes in the data do not represent pixel indexing, but something else, and we can't figure out what. Any ideas what those bytes might represent?
: Any help would be appreciated
: Thank You,