Re: Calculating Scan Size

From: Mike Finley ^lt;>
Date: 02/20/04-01:26:32 PM Z
Message-id: <>

On Fri, 20 Feb 2004 14:11:43 -0500, Jon Danforth <>

>Try using the scan calculator at I use this all the time.
>For instance, scanning a 645 negative at 2400dpi yields these results:
>(2.205 inches x 2400 dpi) x (1.693 inches x 2400 dpi) = 5291 x 4063 pixels
>(10.419 inches x 508 dpi) x (8.000 inches x 508 dpi) = 5291 x 4063 pixels
>This also gives you the equation for calculating it on your own later on.
>To get the size in MB, you'll have to then multiply each value by the number
>of bits per channel (8 or 16) by the number of channels. Then you divide
>multiply the number of bits by 8 to get the number of bytes and then divide
>that number by 1024 to get the number of megabytes.
>So if you have a grayscale image, that's 5291 * 8 = 42328 + 4063 * 8 = 32504
>= 74832 bytes / 1024 = 73.08 MB.
>RGB color is just three times that (roughly). Keep in mind that these
>calculations are based on scanning at 2400dpi.
>There's probably a more simple way of doing it but I'm a bit rushed right
>now. The light outside is AWESOME.

This gives the megabytes of image data in the file, but doesn't
necessarily equate to the file size on the disk, if that was what
Sandy was asking about.
Some formats compress heavily, and throw away data in the process, eg
Some formats compress less heavily and can restore exactly the same
data when opening the file.
Some formats do not compress at all.
Tiff files can be any of the above, depending on options chosen

In addition to the image data there will be a small amount of
additional data needed to identify the contents to software that is
using it.

So if you are talking about file sizes on disk, then there is no
direct correlation to resolution and image size.


Mike Finley,
Received on Fri Feb 20 13:25:27 2004

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