resolution

[Jim Johnston]

I have a new Microtek i800 and what resolution should you use for slides and
plan to put them on dvd for tv viewing. Thanking all Jim Johnston

 

[Lorenzo J. Lucchini]

I have a new Microtek i800 and what resolution should you use for slides
and plan to put them on dvd for tv viewing. Thanking all Jim Johnston

If the only thing you need from your scans is non-zoomed TV viewing, then
only 600 dpi or so will be enough, and 1200 dpi or so will be fine.

But why not do the complete calculation. My 35mm-film slides are 24mm x 36mm
(I don't remember if these are the "official" values, but I think they
are).

PAL television is (supposed to be) 540 lines (vertical resolution), while
the horizontal resolution isn't fixed (DVDs apparently use 720 columns).

So, if you are not going to rotate your slides on the TV screen, you need to
have at least 540 points sampled every 24 millimeters, which translates to
22.5 samples per millimeter, which translates to 571.5 samples per inch.

Nobody says that 571.5 dpi will also be a good choice for the *horizontal*
axis (as, again, TV doesn't really have a fixed "horizontal resolution"),
but as the thing you'll use to convert from digital to analog is probably
going to output square pixels, we can safely assume that if 571.5 dpi is
the correct value for the vertical axis, it will be correct for the
horizontal axis, too.


Still, nobody said that one scanner sample per output pixel is the best
choice. Actually, it can easily be a *poor* choice, because of (among other
things) sensor noise and the possibility of aliasing.

Anyway, one sample per pixel is what you need to "fill in" your TV screen
without a need for interpolation. Keeping in mind the limitations of a TV
screen (pixel crosstalk, blur, etc.) I'd made an educated guess that 571.5
dpi (i.e. one sample per pixel) will be good enough, and going above that
will be made almost useless by the limitation of the TV screen.

Still, if you prefer to be on the safer side, I'd suggest something like
1200 dpi. It's still much less than what people usually scan slides at for
archival, but it will be much more than adequate for viewing on any TV
screen (after, of course, resizing to 571.5 dpi).


By the way, if you aren't using PAL, the calculations will be slightly
different: NTSC, for instance, has 484 scanlines.


by LjL
(e-mail address removed)

 

[-]

If you are new to scanning, a good place to learn the general theory behind
resolution is www.scantips.com. It will also help you to get up to speed
with other aspects of scanning if you are new to scaniing.

Doug

 

[Per Larsen]

Jim Johnston wrote:




If the only thing you need from your scans is non-zoomed TV viewing, then
only 600 dpi or so will be enough, and 1200 dpi or so will be fine.

But why not do the complete calculation. My 35mm-film slides are 24mm x 36mm
(I don't remember if these are the "official" values, but I think they
are).

PAL television is (supposed to be) 540 lines (vertical resolution), while
the horizontal resolution isn't fixed (DVDs apparently use 720 columns).

In my (good) old days of teaching the "inner stuff" television, PAL had about 575 lines shown in the picture (625 totally per frame, but about 25 lines above and 25 lines below each picture used for other stuff, like text tv).

For NTSC it's a bit lower (525 and 487, respectively, according to this url: http://www.divx.com/support/guides/guide.php?gid=10)

PerL

 

[Lorenzo J. Lucchini]

In my (good) old days of teaching the "inner stuff" television, PAL had
about 575 lines shown in the picture (625 totally per frame, but about 25
lines above and 25 lines below each picture used for other stuff, like
text tv).

What I read when I wrote that article was that PAL has 540 "visible" lines,
while it had more if vertical blank was counted in.
Then, it mentioned that the *really* visible lines are something like
520-530 depending on the specific TV screen.

But I might easily have read a wrong source.

Anyway, I think what's really important for the OP is the resolution of a
DVD, since that's what he's going to use... that should be 720x576 (PAL!)
if the sources I'm looking at right now are not wrong.

For NTSC it's a bit lower (525 and 487, respectively, according to this
url: http://www.divx.com/support/guides/guide.php?gid=10)

by LjL
(e-mail address removed)

 

[willie]

The advice you recieved for TV or computer screen viewing is correct.

Another thing to consider are artifacts from improper digitization.
These "aliasing" artifacts can add grain and digital noise to the
images obtained with low resolution scans. This has nothing to do with
the display resolution but involves compromises made during the
digitization.

If your scans look flat (low contrast and dull colors), then scanning
at higher resolution may produce better scans. You can use many of the
popular image processing software programs to downsize higher
resolution images for screen only viewing to save disk space. The
downsizing compromises the image quality less than digitization
artifacts.

wch