How to keep the header and trailer while zlib decompress and compress

I have raw data extracted from PDF and I decompressed the raw data and compressed it again.

I expected the same header and trailer, but the header was changed.

• Original Hex Header

48 89 EC 57 ....

• Converted Hex Header

78 9C EC BD ...

I dug into zlib compression and got header 48 also is one of zlib.header.

But mostly 78 is used for zlib compression.

It's my code which decompress and compress:

decompress_wbit = 12
compress_variable = 6
output_data = zlib.decompress(open(raw_data, "rb").read(), decompress_wbit)
output_data = zlib.compress(output_data, 6)
output_file = open(raw_data + '_', "wb")
output_file.write(output_data)
output_file.close()

I changed the decompress_wbit and compress_variable but still keeps 78.

So not sure how to get 48 as header.

Here is the short description about zlib.header.

• CINFO (bits 12-15)

Indicates the window size as a power of two, from 0 (256 bytes) to 7 (32768 bytes). This will usually be 7. Higher values are not allowed.

• CM (bits 8-11)

The compression method. Only Deflate (8) is allowed.

• FLEVEL (bits 6-7)

Roughly indicates the compression level, from 0 (fast/low) to 3 (slow/high)

• FDICT (bit 5)

Indicates whether a preset dictionary is used. This is usually 0. 1 is technically allowed, but I don't know of any Deflate formats that define preset dictionaries.

• FCHECK (bits 0-4)

A checksum (5 bits, 0..31), whose value is calculated such that the entire value divides 31 with no remainder.

Typically, only the CINFO and FLEVEL fields can be freely changed, and FCHECK must be calculated based on the final value.* Assuming no preset dictionary, there is no choice in what the other fields contain, so a total of 32 possible headers are valid. Here they are:

      FLEVEL: 0       1       2       3
CINFO:
     0      08 1D   08 5B   08 99   08 D7
     1      18 19   18 57   18 95   18 D3
     2      28 15   28 53   28 91   28 CF
     3      38 11   38 4F   38 8D   38 CB
     4      48 0D   48 4B   48 89   48 C7
     5      58 09   58 47   58 85   58 C3
     6      68 05   68 43   68 81   68 DE
     7      78 01   78 5E   78 9C   78 DA

Please let me know how to keep the zlib.header while decompression & compression

Thanks for your time.