COMP 206 Lecture Notes - Lecture 7: Steganography, Binary Image, Digital Image Processing

• School: McGill University
• Department: Computer Science (Sci)
• Course: COMP 206
• Professor: David P.Meger

Document Summary

Lecture 7 binary data: many components of software systems require us to work with the data in raw binary form: How can we read a bmp file using c: what works well, check the magic number: If (cid:449)e ope(cid:374) (cid:449)ith (cid:862)r(cid:863), c (cid:449)ill do so(cid:373)e of this auto(cid:373)ati(cid:272)ally fgets, fscanf also typically bad choices. Recall: binary representation of integers: ea(cid:272)h (cid:862)1(cid:863) (cid:271)it represe(cid:374)ts a po(cid:449)er of t(cid:449)o added to the value, what is the value of this nibble, 1*2^0 + 1*2^1 + 0*2^2 + 1*2^3, = 11. Bitwise example #1: check the value of bit 3, larger example posted to github, bit_reporting. c. More bitwise examples: set the value of bit 8 to 1, cou(cid:374)t the (cid:374)u(cid:373)(cid:271)er of 1(cid:859)s, find the first 0 starting from the right. Back to steganography: e(cid:272)all: if (cid:449)e e(cid:374)(cid:272)ode a stri(cid:374)g (cid:449)ithi(cid:374) the (cid:862)lo(cid:449)est-order(cid:863) (cid:271)its of a(cid:374) i(cid:373)age, it is (cid:374)early invisible, we will examine the example code, posted on github for this lecture, steg_encoder. c, steg_decoder. c.