filmscanners: Re: Hello, thanks, and more.

[Roger Smith <rsmith@unb.ca>]

>Right, but scan at 72 dpi and you get crap.   One day I'll understand
>  >all this.  ;-)

At 1:08 PM -0700 10/22/01, Ken Durling wrote:
>I guess I'm missing the point here.  If I were to scan even a 4x6
>print at 72 dpi, and then want to display it anything larger than
>288x432 pixels, wouldn't interpolation be necessary?  Even more with a
>slide or a negative?

        After reading these various comments about scanning at high 
resolution and downsampling vs initially scanning at low resolution, 
I decided to try it and compare.
        Using a Minoltal Dimage Scan Dual II and VueScan, I scanned a 
Fuji Provia 100F slide that I know to be very sharp. I scanned at 
2820 (native resolution), 1410, 705, and 353 (the lowest that VueScan 
goes, and roughly equivalent to 4x6 inches at 72 ppi). I then set the 
Crop tool to 4x6 inches at 72 ppi and cropped the three higher-res 
scans identically.
        I could immediately see the 353 ppi scan was terrible, as can 
be seen in the enclosed photo. Note the jaggy edges on the steeple. 
The other three scans were remarkably similar, so I have included the 
downsampled 1410 middle resolution scan.
        Thus, it appears at least with the Scan Dual II that scaning 
at higher resolution and downsampling is much preferable to initially 
scanning at a low resolution.
        I noticed the same thing years ago with my Epson 636 flatbed 
when I scanned prints for inclusion in PowerPoint presentations. 
Images scanned at 200 or 300 ppi and downsampled to 72 ppi were much 
better than images scanned at 72 ppi.

Regards,
Roger Smith

Attachment: res_test.jpg
Description: JPEG image