RE: Calculating Scan Size

From: Baird, Darryl ^lt;[email protected]>
Date: 02/20/04-03:36:50 PM Z
Message-id: <>


I always use photoshop to figure sizes. Just make a "New" file and pug
in the dimensions and resolution values until you reach your desired
target size. That's the "free software" inside of photoshop.


-----Original Message-----
From: Sandy King []
Sent: Fri 2/20/2004 3:40 PM
Subject: Re: Calculating Scan Size
My purpose in asking the question has nothing to do with arguing
point. I am making some scans of large 5X7 negatives and want to keep
total file size below 700mb so I can save the raw file to a CD.
Unfortunately the scanning software that I am using does not tell me
the final file size after I indicate resolution and target size, as
some software does.


>Good point. I always scan into an uncompressed 16 bit TIFF so I
didn't even
>think about getting into compression. Mike's right because there
really is
>no easy way to calculate size on disk.
>Those calculations are handy when you get in a digital vs. analog
>and someone brings up megapixels as their only arguing point. My
>Well if you're only counting megapixels then I've got way more on a
>negative than you do.
>----- Original Message -----
>From: "Mike Finley" <>
>To: <>
>Sent: Friday, February 20, 2004 2:26 PM
>Subject: Re: Calculating Scan Size
>> On Fri, 20 Feb 2004 14:11:43 -0500, Jon Danforth
>> wrote:
>> >Sandy,
>> >
>> >Try using the scan calculator at I use this all
the time.
>> >
>> >
>> >
>> >For instance, scanning a 645 negative at 2400dpi yields these
>> >
>> >Input
>> >(2.205 inches x 2400 dpi) x (1.693 inches x 2400 dpi) = 5291 x
>> >Output
>> >(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
>> >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
>> >that number by 1024 to get the number of megabytes.
>> >
>> >So if you have a grayscale image, that's 5291 * 8 = 42328 + 4063
* 8 =
>> >= 74832 bytes / 1024 = 73.08 MB.
>> >
>> >RGB color is just three times that (roughly). Keep in mind that
>> >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.
>> >
>> >-Jon
>> >
>> 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,
>> Some formats compress less heavily and can restore exactly the
>> 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
>> using it.
>> So if you are talking about file sizes on disk, then there is no
>> direct correlation to resolution and image size.
>> mike
>> mike
>> Mike Finley,

Received on Fri Feb 20 15:45:41 2004

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