filmscanners: Re: File sizes, file formats, etc. for printing 8.5 x 11and 13 x17...

[Roger Smith <rsmith@unb.ca>]

At 8:44 AM -0600 2/27/01, Marvin Demuth wrote:
>As I prepare for scanning for these size prints, it will help me, and I
>suspect others, if some of you scanning for quality 8.5 x 11 and 13 x 17
>prints from 35mm in either b & w or color will comment on:
>
>1. The typical file sizes you use at the printing stage and the ppi of your
>final scans.
>2. The file format of the file at the printing stage.
>3. How you archive your final scans used for the printing, i.e. CDs, etc.
>4. The bpi and ppi confusion.

Hi Marvin,
        You will probably get a number of different opinions on this, 
and they may all be good.

        1. In my case, I always scan at the optical resolution of the 
scanner (2720 ppi with my Canon FS 2710). This gives a file of about 
26.5 Mb (assuming you are using an 8-bit file).
        For printing I resize to the size I want in Photoshop's Image 
Size ("Resample Image" unclicked) and let the resolution fall where 
it may. There have been many discussions on the "ideal" image file 
resolution for Epson printers, but the consensus seems to be 
somewhere between 240 ppi and 360 ppi. My tests showed that there was 
some improvement in going up from 240 to 300 to 360, but that there 
was no degradation of the print using odd resolutions such as 347 ppi 
or 353.753 ppi. Some people have claimed that using odd values for 
resolution affects the quality of their prints, but I haven't found 
that to be the case.
        As it happens, 360 ppi gives you about 10.3 x 7, which is the 
maximum printable length on the Letter setting, and 240 ppi gives 
about 10.5 x 15.5, a handy size for A3 or 11x17 paper.
        2. I usually use .psd files for printing, but .tifs do as well.
        3. I archive on CD-Rs. The consensus here seems to be to use 
gold-dye CD-Rs for maximum file stability. Good formats again include 
.psd or .tif, but TIFFSs can be read by more image programs than 
Photoshop documents.
        4. I'm not sure what you mean. Do you mean dpi? If so, dpi is 
a convention used by printers, but it is less meaningful with 
printers such as Epsons, which use a random dithering pattern to lay 
down ink drops. The common values of 720x720dpi or 1440 x720 dpi used 
by Epson don't mean much, except that 1440 usually gives a smoother 
output with less horizontal banding. It refers to a smaller 
incremental movement of the paper as it goes through the printer, not 
that the printer is putting out more dots of ink per inch.
        Ppi is strictly a digital notation that describes the number 
of pixels making up an image. For example, a raw scan from a Canon 
FS2710 is 2720 ppi, but if you printed the image, it would  only be 
about 1x1.5 inches, the size of a 35mm frame. That makes the number 
of pixels about 2600 by 3700, or about 26.5 Mb (depending on how 
close to the edge it is cropped). Thsi information shows up in the 
Image Size box. As noted above, this image can be resized at will - 
lowering the resolution automatically increases the size it will 
print. This makes no difference to how it looks on your monitor - 
Photoshop for example always shows a % number at the top of the 
screen. This relates to how image pixels relate to screen pixels. 
This gets complicated by what resolution your monitor screen is set 
to, so I'll leave it at  that. For the most accurate view of your 
image, use100%, as this gives one screen pixel for each image pixel. 
You will find your images look better at the even divisions of 100% 
(12.5%, 25%, 50%) than at the odd numbers like 33.3% and 66.7%.
        I hope this isn't too confusing. I see other answers are 
starting to appear, so I'll leave it here.

Regards,
Roger Smith