[sane-devel] Stated scanner resolution. Was: Legal-size scanner recommendations?

[abel deuring]

On 12.02.2010 14:16, emre wrote:
> abel deuring wrote:
>> *On 12.02.2010 05:12, emre wrote:
>>  
>>>
>>> I have one more question, it has to do with resolution.  The fi-6130
>>> reports a 600 dpi
>>> resolution (which seems to me to be more than sufficient).  I have seen
>>> some Epson
>>> scanners that report 6400 dpi.  I am guessing that higher resolution
>>> might be good
>>> for slides and photos, but wouldn't be of much use for scanning
>>> documents?
>>> Thanks again,
>>>     
>>
>> I have serious doubts that even any affordable slide scanner really has
>> such a high resolution; for a scanner that can scan an A4 or letter size
>> document, 6400 dpi sounds ridiculous. You would need very precise and
>> expensive optical and mechanical components to really achieve such a
>> high resolution.
>>
>> Also, consider the size of an A4 size scan with 6400 dpi: That would be
>> 210*297*6400*6400/(25.4*25.4), nearly 4 billion pixels. IOW, you could
>> fill a terabyte disk with just 250 uncompressed gray scale images...
>>
>> Typical scan resolutions for A4/letter size are 200 or 300 dpi -- what
>> you need depends on your use case, the number of scans you want to store
>> and on the storage capacity you can and want to afford.
>>
>> Abel
>>
>>   
> I just verified at the epson.com website for the Epson Perfection V600
> printer, and they
> do report 6400 dpi for their optical resolution.  Granted, it would take
> a lot of disk space,
> but it would also seem beneficial to have this resolution for archiving
> of slides and negatives.

Sure, it might be nice to scan slides with that resolution. But even
then: IIRC, the "resolution" of most slides is more like 2000dpi than
6000dpi. So, unless I am completely mistaken about the, how is is
called, grain size?, of slides or negatives, 6400dpi looks a bit
pointless. Also, I'd be really curious how a scan of a high-quality
Siemens star (http://en.wikipedia.org/wiki/Siemens_star) looks like for
these allegedly possible 6400dpi. Frankly, I'd suspect that the image
will look quite blurry, if you look at it closely enough.

> Now, if they really have this resolution, I can not say... & I am

I can't say either, of course ;) Sure, I believe them that the _data_
produced by scanner will have 6400dpi resolution -- I just doubt that
you can really get such an _optical_ resolution with a scanner that
costs less than, let's say, a good second hand car...

Abel