35mm Slides: What DPI?

[Wayne]

Pete, what you want to do with the image? The job requirement is what
determines image size needed to do the job.

For example, maybe you want to show it on the video screen. That would be a
smallish image, maybe 800x600 pixels in size. Maybe a bit smaller for email,
or maybe a bit larger for a large screen, but any larger than the screen is
pointless.

Maybe you want to print a 4x6 inch print.
1200x1800 pixels will print 4x6 at 300 dpi.

Maybe you want to print a 8x10 inch print.
2400x3000 pixels will print 8x10 inches at 300 dpi.

Then you use whatever scanning dpi that will give the image size needed.

 

[(PeteCresswell)]

VueScan 8.1.3, Kodachome.

Of course I don't need or want 4000, but the 300 or so I get on "Auto" seems a
bit lacking.

Does anybody have a ballpark figure for not-exactly-technically-brilliant
slides?

 

[(PeteCresswell)]

Per (PeteCresswell):

Does anybody have a ballpark figure for not-exactly-technically-brilliant
slides?

1333 seems tb a decent balance between detail and JPEG file size, but I'm saving
at max JPEG quality.

Maybe there's some more balancing to do between DPI and JPEG quality?

 

[(PeteCresswell)]

Per (PeteCresswell):

Maybe there's some more balancing to do between DPI and JPEG quality?

4,000 dpi at JPEG 75 gives files that are consistantly a little less than 2
megs...

 

[Charlie Hoffpauir]

Per (PeteCresswell):

1333 seems tb a decent balance between detail and JPEG file size, but I'm saving
at max JPEG quality.

Maybe there's some more balancing to do between DPI and JPEG quality?

As always, the answer is "it depends on the intended use". If you
never want to make a large print, and you don't intend to do any post
processing, then your 1333 ppi saved as highest quality jpeg should do
nicely, scan quite fast, and use little disc space. However, if ANY of
the above is NOT the case, you may want to scan at the highest optical
resolution of your scanner and save the scanned image as a lossless
TIFF file, post process that image, and archive that copy also. Then
use a lower res copy saved as a JPEG for whatever else you want (slide
show, screen saver, etc.)
Charlie Hoffpauir
http://freepages.genealogy.rootsweb.com/~charlieh/

 

[(PeteCresswell)]

Per Charlie Hoffpauir:

your 1333 ppi saved as highest quality jpeg should do
nicely, scan quite fast, and use little disc space. However, if ANY of
the above is NOT the case, you may want to scan at the highest optical
resolution of your scanner and save the

No post processing forseen, but when I browse the pix via ThumbsPluss, I do a
lot of zooming.

The combination I've settled on is a 4000 DPI scan and a "80" JPEG save.
For 35mm, this gives a files around 2 megs - which I find acceptable. The
surprise for me was the great reduction in size when I moved from max quality
JPEG (12 megs) to "80" (2 megs).

I suppose 80 introduces compression artifacts, but the ability to zoom to just
about the limit of the camera's resolution outweighs any artifacts.

If I were a better photographer and/or was using better equipment when the
slides were made, I'd probably be looking for better rez on the scans - but for
what I've got, 4,000/80 seems tb the choice.

 

[Charlie Hoffpauir]

No post processing forseen, but when I browse the pix via ThumbsPluss, I do a
lot of zooming.

I've seen very few scans that I couldn't improve significantly with a
little post processing. I'll make you a deal.... send me a scan that
you are a bit disappointed with in the exposure, or one that looks a
little flat, and I'll minimally adjust it and send it back to you.
Send it to my yahoo mailbox... charliehoffp at yahoo dot com.
Charlie Hoffpauir
http://freepages.genealogy.rootsweb.com/~charlieh/

 

[Jim]

VueScan 8.1.3, Kodachome.

Of course I don't need or want 4000, but the 300 or so I get on "Auto" seems a
bit lacking.

Does anybody have a ballpark figure for not-exactly-technically-brilliant
slides?

Thyis depends on what size of print you expect to make.
If, for example, you want to make 11x14 prints at 300 dpi, then the scan
must be at 3300 dpi or slightly more.
Jim

 

[j4h]

Thyis depends on what size of print you expect to make.
If, for example, you want to make 11x14 prints at 300 dpi, then the scan
must be at 3300 dpi or slightly more.
Jim

 

[j4h]

wally here, this is what I have been trying to inquire about; the
epson 2480 photo has a choice when scanning in home mode. (a)
resolution (b) target size. Is 300 ppi or dpi as epson calls it okay
for (a) and 11x14 okay for (b). In other words, is that the same as
3300 dpi scanning. Sometimes it seems like people are saying you have
to scan at 4000 ppi at original size on 35mm slides and target size is
not mentioned. Thank-you for any answer.

 

[Wayne]

wally here, this is what I have been trying to inquire about; the
epson 2480 photo has a choice when scanning in home mode. (a)
resolution (b) target size. Is 300 ppi or dpi as epson calls it okay
for (a) and 11x14 okay for (b). In other words, is that the same as
3300 dpi scanning. Sometimes it seems like people are saying you have
to scan at 4000 ppi at original size on 35mm slides and target size is
not mentioned. Thank-you for any answer.

Wally, the basics are that the the ratio of scanning resolution/printing
resolution is the enlargement factor. Also the ratio of target/original
size is enlargement factor. For example, 35 mm film is 24x36 mm, or
roughly 1.4 x 0.92 inches. If you want to print 11x14 inches, then that
is an enlargement factor of 11/0.92 inches = 12x enlargement.
Therefore, if you want to print at 300 dpi, then scan this at 12x300 =
3600 dpi. This 12x is BOTH the ratio of target/original size, and the
inverse ratio of scanning/printing resolution.

You can scan this two ways. You can scan at 3600 dpi 100% scale, and
scale it yourself to 11x14 inches later.

Or you can set the scanner to 300 dpi and 12x enlargement (1200%)
and this means it will scan at 300x12 = 3600 dpi,
and it will come out of the scanner scaled that way (11x14 at 300 dpi).

However, the 2480 is a 2400 dpi scanner, its optical maximum is less
than 3600 dpi. That means you can print 12x size at 2400/12x = 200 dpi.

 

[j4h]

okay I was using the last msg as an example. re 11x14 and 3300 dpi. So
on my 2480 epson, if I set it at 300 dpi res. and 4x6 target size in
the home mode, am I scanning at what everyone would call over 1000 ppi
resolution. thank - you

 

[One4All]

Wayne wrote:

That means you can print 12x size at 2400/12x = 200 dpi.

Wayne,

How much difference in print quality is there between printing at 300
dpi & 200 dpi? Would any difference become more noticeable at a target
size of 16 x 20" vs. 4 x 6"?

 

[j4h]

Wayne wrote:

That means you can print 12x size at 2400/12x = 200 dpi.

Wayne,

How much difference in print quality is there between printing at 300
dpi & 200 dpi? Would any difference become more noticeable at a target
size of 16 x 20" vs. 4 x 6"?

 

[j4h]

I'm still just a real amateur at this. I was trying to figure out what
a reasonable resolution is. e.g. 300 or a very much higher number like
in the thousands. I just want to scan my slides at a resolution that
is right because of all the time it will take. All the ads say you
need to scan at 4000 which I can't even do. But I'm starting to realize
that a 300 ppi number on my 2480 eson scanner is actually more like
1200 (depending on the target size). It does not use numbers like 12X.
in the home mode. If I'm all wrong I'd like to hear about it. thank-you

 

[Erehwon]

If you know what the final size is just specify that size and 300 dpi. The
scanner software will do the math and attempt to scan at the necessary
resolution. If it doesn't have enough resolution, the picture's going to
come up with less than the 300 dpi requested, but it's still the best you
can do.

If you specify a target size of 3X5 with 300 dpi, the scanner will try to
get 3 in @ 300 dpi or 900 dots by 5 in @ 300 dpi =1500 dots.

The slide is about 1.4 in X .92 in so the scanner is really going to try to
scan at 1500 dots / 1.4 in = 1071 dpi or 900 dots /.92 in = 978 dpi so
about 1000 dpi.

So, specifying a 3X5 target size at 300 dpi gives you about the same quality
scan as specifying a target size "same as original" (1.4in X .92 in) at 1000
dpi.

If you try to crop or blow up that picture, however, you still have the
original number of total "dots" and now your going to spread them out over a
larger area giving much less than a 300 dpi print which will look much
worse. Same thing if you want a target size that requires more actual dpi
than your scanner resolution can provide.

 

[Wayne]

okay I was using the last msg as an example. re 11x14 and 3300 dpi. So
on my 2480 epson, if I set it at 300 dpi res. and 4x6 target size in
the home mode, am I scanning at what everyone would call over 1000 ppi
resolution. thank - you

If you are scanning 35 mm film, then an output target of 4x6 inches is
an enlargement factor of about 4 inches / 0.92 inches = 4.3x size.

So if you set the scanner to 300 dpi, and 4x6 inches output, then it
should also show about 430% scale, and will actually be scanning at
300 dpi x 4.3x = 1300 dpi.

 

[Wayne]

Wayne wrote:

That means you can print 12x size at 2400/12x = 200 dpi.

Wayne,

How much difference in print quality is there between printing at 300
dpi & 200 dpi? Would any difference become more noticeable at a target
size of 16 x 20" vs. 4 x 6"?

Not much, but a little. 200 dpi might be a bit less great in a AB
comparison with 300 dpi. Or it might not be noticable to some people or
with some subjects. Some people with smaller digital cameras think 100
or 150 dpi is "great", but they probably never saw 300 dpi.

But if a spacing of 200 pixels per inch is all the pixels you have, then
that's all you can do. If not enough pixels, you either print a smaller
size (inches) or you print the larger size at a lower pixels per inch
spacing. Pixels per inch is the simple formule pixels / inches.

 

[Wayne]

I'm still just a real amateur at this. I was trying to figure out what
a reasonable resolution is. e.g. 300 or a very much higher number like
in the thousands. I just want to scan my slides at a resolution that
is right because of all the time it will take. All the ads say you
need to scan at 4000 which I can't even do. But I'm starting to realize
that a 300 ppi number on my 2480 eson scanner is actually more like
1200 (depending on the target size). It does not use numbers like 12X.
in the home mode. If I'm all wrong I'd like to hear about it. thank-you

Right, the dpi number you enter into the flatbed software is the Printing
resolution at target size. The scanning resolution dpi number is the
product of that printing resolution multiplied by the scale factor of the
output target size (usually not shown). If the scale factor field says
100% (target size is original size), then the two resolutions are the
same number.

What size to scan has no answer until you specify your goal for using the
image. If you will only show the image on the video screen, then the
image size (dimensioned in pixels) should not be larger than the video
screen size (dimensioned in pixels). If you will print on paper, it
depends on the size you will print it - 4x6 inches at 300 dpi is
1200x1800 pixels, or 8x10 inches at 300 dpi is 2400x3000 pixels.

When you know your goal, then that is the size image you need.

 

[Kennedy McEwen]

I'm still just a real amateur at this. I was trying to figure out what
a reasonable resolution is. e.g. 300 or a very much higher number like
in the thousands. I just want to scan my slides at a resolution that
is right because of all the time it will take. All the ads say you
need to scan at 4000 which I can't even do. But I'm starting to realize
that a 300 ppi number on my 2480 eson scanner is actually more like
1200 (depending on the target size). It does not use numbers like 12X.
in the home mode. If I'm all wrong I'd like to hear about it. thank-you

To avoid any confusion, simply set the output size to the size of the
original material and then scan at the optical resolution of the
scanner, which in your case is 2400ppi. So, if you have 35mm film, set
the output size to 36x24mm (1.417x0.945inch) or a scale of 100% and then
scan at 2400ppi.

When you come to print the resulting files you can specify the size
and/or output ppi of the output image with almost any printing package
at that point, completely independently of the scale you scanned it at.

The important issue is that you scan your slides with the capability of
the input equipment you have now. Forget trying to guess what the
capabilities of the output equipment you might have in the future will
be or what size you might ultimately choose to print at. The only thing
you can guarantee about that is that sooner or later the guess will be
wrong.

If you find a guaranteed method of predicting what you will have and
want in the future, you would make better use applying it to the
racecourse or the lottery - then you will be able to pay someone else to
scan your slides from your profits! ;-)