Humongous file sizes in scanning

Status
Not open for further replies.

Darthvader

Back From Deathstar
can anyone tell me why any scanned image file of 600 dpi occupies a huge space of my 200 mb on my new benq scanner
 

pimpom

Cyborg Agent
Any digital image, whether scanned or otherwise, is an arrangement of small square blocks or dots called pixels. The smaller the pixel, the finer the image; but the total number of pixels is greater.

dpi = dots per inch. The higher the dpi you use to scan an image, the more bits of information it records, resulting in a larger file size.

To be more precise : Suppose you scan an image of 2"x2" size. At 100dpi, you have 200 dots across and 200 dots down, and you get 200x200 = 40,000 dots. Like this -
...............
...............
...............
...............
...............

If you scan the same picture at 600 dpi, it will have 1200x1200 dots, a total of 1,440,000 dots.

To be meaningful, each dot has to have its own shade of colour. If you scan at 24-bit colour, each dot has its colour information stored as a 24-bit piece of data. Therefore a 2"x2" picture scanned at 100dpi at 24-bit colour depth is represented by 40,000x24 = 960,000 bits of data.

At 600 dpi, the same picture is represented by 1,440,000x24 = 34,560,000 bits of data.

8 bits = 1 byte.
So the 100 dpi picture occupies 960,000/8 = 120,000 bytes = 120 KB.
The 600 dpi picture size is 34,560,000/8 = 4,320,000 bytes = 4.32 MB.

A 10" by 8" picture scanned at 600dpi and 32-bit colour = 115.2 MB !!
The file size can be reduced by compression techniques, but it results in some loss of quality.

A full explanation will be too long to post here, but I hope you get the idea.
 

tuxfan

Technomancer
Great explanation pimpom. I came here to post something like this. But I couldn't have explained it as good as you :)
 
Status
Not open for further replies.
Top Bottom