I'm trying to build some code I can use to convert a GIF file to another file format (which I already know how to create. [I am trying to streamline conversion from GIF to GRF - a printer graphic file format.])
I am working off of information from Wikipedia (http://en.wikipedia.org/wiki/Graphics_Interchange_Format#Image_coding).
There is a section that describes converting from bytes to 9-bit codes. The examples they show are:
9-bit binary Bytes
(hex) (hex)
00000000 00
100
0101000|1 51
028
111111|00 FC
0FF
00011|011 1B
103
0010|1000 28
102
011|10000 70
103
10|100000 A0
106
1|1000001 C1
107
10000011 83
00000001 01
101
0000000|1 01
I am able to generate the bytes given on the right side from the file. (I created a file exactly the way they described in the article (3x5 with black pixels in 0,0 and 1,1 in MSPaint.)
What I am not understanding is how they are converting these bytes to the 9-bit hex codes.
How does 00 become 100? What does the bar (|) in the binary mean?
Just realized what is happening...
00000000 00 Add the next digit to the beginning - 100000000 = 100
100
0101000|1 51 Next Digit - 000101000 = 028
028
111111|00 FC -011111111 = 0FF
0FF
00011|011 1B -100000011 = 103
103
0010|1000 28 -100000010 = 102
102
011|10000 70 -100000011 = 103
103
10|100000 A0 -100000110 = 106
106
1|1000001 C1 -100000111 = 107
107
10000011 83
00000001 01 -100000001 = 101
101
0000000|1 01