Seeker said:
"HI" to you too Jayelles!
Good for you. The message was of course "HI".
Graphics are made up of little dots called pixels. This image uses 24 bit colour - which means that the colour information about every pixel is stored using 24 binary digits - which means we can use over 16 million colours in the image. For example, if you used 2 bits to store each colour - you could have 4 colours - 00 01 10 and 11. 3 bits would have 8 colours - 000 001 010 011 100 101 110 and 111. The formula is 2 to the power number of bits.
This is more colours than the human eye can differentiate between - but they are quite different to a computer.
So I made the background white - code 255 255 255 and wrote the message in a slightly different shade of white - code 254 254 254. Total different codes to a computer which would see them as the following bit patterns:-
background pixels - 111111111111111111111111
message pixels- 111111101111111011111110
a graphics program would allow you to show the colours or to replace one colour for another colour - thus revealing the message. If for example, you used the software to change all the 254 254 254 pixels to (say) 255 0 0, then the message would show in red. - you could say it was "digitally enhanced" to make it clearer.
In forensic audio analysis - a sound is "sampled" at intervals (tens of thousands of samples per second) and stored in bit patterns - in much the same way as above. Tiny changes in these bit patterns would be detected by the computer even they cannot be heard by the human ear. Analysis of a sound recording such as this is performed using a piece of equipment called a spectrograph.
It is therefore nonsense to claim that a "trained ear" is all that is necessary to determine the presence of voices on the 911 tape. Sophisticated computer equipment is used by the top forensic audio labs.
If you were to use fewer bits to store each pixel in a graphic, then the number of colours would be reduced. The software would work to a set palette of colours and pixel colours might change slightly. This change may be imperceptable to a human eye but nevertheless, the colour would be different.
Same with sound. If a sound is converted from analogue to digital and stored using (say) 16 bit sampling resolution, then only 16 bits worth of the sound sample could be stored and no matter how much a person tweaked the sound or saved it onto a computer with a 24 bit sound card - minute sound detail would be lost forever.