SOT: Scanning old computer docs

[Guy Dunphy]

At 12:19 AM 3/04/2021 -0600, you wrote:
>On 4/2/21 10:27 PM, Guy Dunphy via cctalk wrote:
>> There are defects in your 'good' flatbed image too - for eg the 
>> bleed-through of the orange lettering on the other side of the 
>> sheet. The way to correct that is to use a black, highly light 
>> absorbent backing sheet. Eg black velvet.
>
>Hum.
>
>Why do so many scanners come with glossy white (usually on foam) backing 
>to hold the image down?
>
>I'm questioning why they do that, not your recommendation.

I think it is a combination of habit, and marketting/customer expectations.
People intuitively expect the white backing, and for many scanning tasks
it is preferable. Yet for scanning anything printed on both sides of thin
paper, it's a real problem. 

I have a sheet of matt black plastic, and some black velvet cloth for this.
The plastic is easier to use, but the velvet works better for really
thin paper with a lot of visual bleed through. The more light absorbent
the better. If I ever find a sheet of 'vanta black' (new light absorbent
substance, very close to 100%, look it up) I'll be using that.

That's not the only 'strange & unfortunate lack' in typical scanners.
Another is that the raised plastic bezel goes all the way round the glass,
rather than having at least one of the glass long sides be flat right
to the edge, with the scanner sensor also going very close to the edge.

This is needed for scanning sheets larger than the bed, and also very
essential for scanning pages of books that are too thick to allow getting
any page flat on the typical scanner bed.
There are special 'edge scanners' that allow this - draping the book over
the side of the scanner, so one page can be fully flat on the glass.
They cost _much_ more than normal scanners. And yet the actual
construction has very little that would cost more to manufacture. 
Construction is just arranged a little differently. The higher cost is
another case of 'marketting.'

Guy