basic question regarding pixels and bits

[yuvalkesi]

Hi,
I've got rather basic question, and things don't add up to me... I hope it's the right forum.
If I have a screen of, let's say, 9 pixesl by 9 pixels.
Each of these 9 pixels can be represented by 4 bits, so the total address bus is 8 bits wide (both axes are 4 bits each).
Now, from a different point of view, the total sum of pixels is 81 pixels, and that is 7 bits wide...
So something is wrong here, obviously.
Please clarify.
Thx.

 

[srizbf]

9x9 pixels =total 81 pixels. you are right.

but how do you want to access individual pixel?

straight by numbering each pixel individually ? then from 0 to 80(tot 81 pixels) , you require 7 bits to address individual pixel.

but when you use row and column address for referring individual pixel ,
row requires 4 bits and col require 4 bits.(tot 8 bits)

since it is easy to refer individual pixel by (row and col ) addressing , we usually use that method.

 

[iVenky]

Hi,
I've got rather basic question, and things don't add up to me... I hope it's the right forum.
If I have a screen of, let's say, 9 pixesl by 9 pixels.
Each of these 9 pixels can be represented by 4 bits, so the total address bus is 8 bits wide (both axes are 4 bits each).
Now, from a different point of view, the total sum of pixels is 81 pixels, and that is 7 bits wide...
So something is wrong here, obviously.
Please clarify.
Thx.

Nothing is wrong here, obviously. Did you notice about the unused addresses? The unused addresses in 8 bits is more than in 7 bits. Now if you consider that 9x9 as say something like 11x8 (note that some are unused) then you can do that by using 7 bits. The thing is we usually prefer the best method.

HTH

Regrads,
iVenky