Art,
I really am not trying to pick on you (ok, yes I am); scanners techically
measure resolution in terms of samples per inch or spi. Thus, Your
correction below is wrong.
"That would mean if the scanner claimed a 4000 dpi (really ppi or
pixels per inch) resolution...."
It is really 4000 spi and not ppi.
> But yes, the file size grows 4x if
> the scanner resolution is doubles, assuming the same bit depth
> capture is used.
I think that he was asking more about if this causes an increase in the
image size and not the file size; but I could be wrong.
filmscanners_owner@halftone.co.uk wrote:
> Most color film scanners use a CCD chip which has a series of three
> lines across it each with a color filter over it, Red, Green or Blue,
> which each are made up of a series of sensors. (Nikon uses a slightly
> different method, but I don't want to confuse things).
>
> That line contains a specific number of sensors across it. For
> simplicity, let's assume a film frame is one inch across by 1.5" wide.
> That would mean if the scanner claimed a 4000 dpi (really ppi or
> pixels per inch) resolution, the image dimensions when a file was
> created would be 6000 pixels by 4000 pixels.
>
> The film or sensor stage is moved one pixel width per scan cycle until
> 6000 cycles (for a 1.5" "long" film frame) are achieved.
>
> The image is actually projected onto the CCD sensor, so the sensor's
> length might be larger or smaller than the film dimensions.
>
> If the exact same sensor was used in a medium format film scanner,
> which had, say a 2" wide film frame, that would be scanned at 2000
> ppi, since the same number of sensors would be reading information
> projected on it from a film frame twice as wide.
>
> I have simplified this process. But yes, the file size grows 4x if
> the scanner resolution is doubles, assuming the same bit depth
> capture is used.
>
> Art
>
> Bill0786@tconL.com wrote:
>
>> I'm a bit perplexed at what the dpi means on a film scanner. Trying
>> to compare apples to apples, will a 4000 dpi Brand X film scanner in
>> theory produce a better quality image outputted than a 2000 dpi
>> Brand X scanner, given that the output resolution is the same, say
>> 1600 x 2400 pixels?
>>
>> Or does it simply mean the 4000 dpi scanner will output a much larger
>> image than the 2000 dpi model?
>>
>> Thanks for clearing this up,
>> Bill
>>
>>
>
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