# DPI to file size question - pls help (1 Viewer)

#### Flop21

##### Well-Known Member
"An image scanned at 600 dpi has an image size of 16 MB. What would be the expected file size if it was rescanned at 300 dpi?"

I thought I could just go, x/300 = 16/600, thus x = 8 MB. But that's wrong.

The answer is 4 MB... but how?

This is an industrial technology multimedia question, but hoping someone can help me out even if they don't do the subject.

[Also if math isn't even mentioned in the syllabus, why is this a HSC question? DPI also is not in the syllabus, colour depth and binary digits are though - but as far as I know... DPI does not equal colour depth right?]

#### BLIT2014

##### The pessimistic optimist.
Moderator
Well first of 600DPI, is 600*600 (Square)

That means if you change it to 300DPI, it is 300*300 (Square)

(300*300)/(600*600)=1/4

Therefore, if 600DPI has an image size of 16MB, as it the other image has 1/4 of the information.

You would go 16 * 1/4 =4MB

#### Flop21

##### Well-Known Member
Well first of 600DPI, is 600*600 (Square)

That means if you change it to 300DPI, it is 300*300 (Square)

(300*300)/(600*600)=1/4

Therefore, if 600DPI has an image size of 16MB, as it the other image has 1/4 of the information.

You would go 16 * 1/4 =4MB
Ohhhh, right. I was thinking the DPI was already a square, but it's not.

Thanks!