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What resolution for scanning slides?

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Anonymous
June 25, 2005 3:16:04 PM

Archived from groups: rec.photo.digital (More info?)

What is the consensus on 'best' resolution setting for 35 mm slides
please?

In Control Panel>Properties>Scanners & Cameras>Epson Perfection 2480,
I see my new scanner is specified as 2400/4800 dpi. The 'default'
setting in the Resolution box always seems to be 300. Using the Fully
Automated Mode I cannot see what resolution has been used. In
Professional Mode, which I am now experimenting with, if I use 2400 I
get what appear to be good quality results. But I notice that the file
size in that case is typically about half of that using Full Auto. So
I'm wondering if that means Auto uses 4800? Come to that, what does
'2400/4800' actually mean anyway?

--
Terry, West Sussex, UK
Anonymous
June 25, 2005 3:16:05 PM

Archived from groups: rec.photo.digital (More info?)

Hello Terry

It's accepted that an input value of 4000 ppi is best simply because it
covers all possible uses for the final image and wrings as much
information as possible from the neg or slide. 4000 ppi is the way to
go for larger print sizes and detailed editing requirements. 300 ppi
(it will probably read dpi) is the output resolution for home printers
and professional digital equipment that produce digital prints.

Each print size requires a minimum number of pixels at 300 ppi
resolution to ensure the best resolution. Beyond this, the resolution
is just wasted - you'll never see it. So ideally, a 7x5 print should be
around 2100x1500 pixels. If you ask too few pixels to fill too big a
space for a specific print size, the image will start to break up with
the individual pixels becoming more obvious.

See here: http://www.theimageplane.net/interp.htm

The bad news for you is that the image quality of flatbed film
attachments fall some way behind dedicated film scanners, so for
optimum results it's best to use a scanner specifically designed to
scan 35mm film. However, if you're producing smaller prints, you may
well find that your scanner will deliver good results if you scan for
reasonable detail.

Hope this helps.

:o )
Anonymous
June 25, 2005 3:16:05 PM

Archived from groups: rec.photo.digital (More info?)

Hello Terry

I would think your scans would produce prints you'll be delighted with.
It won't be in the same league as dedicated film scanners, but judging
by these scans it will do a really good job! A flatbed scanner won't
compete with a film scanner resolution wise, but scan at the best
resolution you can without any digital trickery (the adding of pixels).

But there are a couple of issues here:

Firstly, if you're sure you will not be needing very large prints, scan
at a resolution that will deliver the best print results, as we
discussed above - 300 dpi (ppi) is the norm with film scanners. Or, to
put it another way, it wouldn't make sense to scan at a 2400 dpi input
value if you're only wanting 7x5 prints. The maths here works out at
2100x1500 for optimum results for 7x5s. Divide your pixels by 300. I
routinely scan at 4000 ppi input (@ 300 ppi output) because I know I
can use the images for *every* purpose. If I need a big 18x12, no
problem. If I need a small image for the website, no problem. If I need
a 9x6, no problem. However, if I scan too small I'm snookered if I want
a really big print.

Your images are scanned in at 96 dpi. Just do the maths to make sure
that the correct number of pixels is present in any image per print
size before you get your prints done. If film is canned at 300 ppi,
software can show its dimensions in inches. For example, a recent scan
of mine is 5557x3640, which when shown in inches is 18.5233x12.1333, so
I know what maximum print size I can get.

Some consumer labs will produce print sizes in relation to submitted
image sizes that go way below 300 ppi as a minimum requirement, and
many are more than happy enough with the results. I can see it though.
Get below 200 ppi and things start to really go downhill. But it
doesn't make sense to compromise resolution in this way unless you're
just after 'happy-snappies', and there's nothing wrong with that, of
course!

A second point: JPEG compression quality refers to the amount of data
the software loses when it saves the image. This is why JPEGs are used
for web pages. In terms of KBs, they can be quite small but still look
ok. But if you compress too much you'll lose too much data and the
detail and colour will go out the window. I recommend you set it to the
very best quality possible, or even better, save your scans as TIFFs
and convert to a JPEG when you have worked at the image, if that's what
you intend to do.

"The JPEG standard was written by the committee known as the Joint
Photographic Experts Group, and it was designed for compressing full
color or grayscale images (in particular, photographs and similar
high-quality artwork). JPEG is a 'lossy' file format; when the JPEG
algorithm compresses the image, it reduces the size by chucking bits of
the image away. How does it know what to lose? JPEG compression plays
on the fact that the human eye can only see so much. We have trouble
seeing small color changes, so JPEG loses some of this subtle
information" (Una Dooney).

I would express the difference between dpi and ppi like this: "The
resolution of a digital image is measured in pixels per inch, not dots
per inch. Software may show the image resolution as DPI, but strictly
speaking this is not correct. Unfortunately, the two terms - ppi and
dpi - tend to be used interchangeably, even by some professionals.
Dpi refers to a printer's output resolution, not the resolution of a
digital image." There are no "dots" in a digital image, just pixels.

Hope I haven't missed too much. Not too much time at the moment, but
feel free to email me through the site if you feel I can be of any use.


Good luck with those scans!
Related resources
Anonymous
June 25, 2005 3:16:06 PM

Archived from groups: rec.photo.digital (More info?)

Hello all,
How does this compare to 4x5 transparencies? For example, with an output of
300dpi and a scanner that can capture 2400dpi and a 4x5 inch transparency is
it correct to say I can make a print of 30 inches ( 2400x 4= 9600dpi,
9600dpi divided by 300 dpi = 32 inches)?
I am also trying to learn the basics of digital printing and scanning.
Since I shoot 4x5 I need to get a flatbed scanner( cannot afford the price
of a drum scanner). Any thoughts on epson's 4990 or microtek's i900
(glassless)?
Thanks
Ed Margiewicz
"Sharp Shooter" <theimageplane@uk2.net> wrote in message
news:1119707391.381286.69410@g14g2000cwa.googlegroups.com...
> Hello Terry
>
> I would think your scans would produce prints you'll be delighted with.
> It won't be in the same league as dedicated film scanners, but judging
> by these scans it will do a really good job! A flatbed scanner won't
> compete with a film scanner resolution wise, but scan at the best
> resolution you can without any digital trickery (the adding of pixels).
>
> But there are a couple of issues here:
>
> Firstly, if you're sure you will not be needing very large prints, scan
> at a resolution that will deliver the best print results, as we
> discussed above - 300 dpi (ppi) is the norm with film scanners. Or, to
> put it another way, it wouldn't make sense to scan at a 2400 dpi input
> value if you're only wanting 7x5 prints. The maths here works out at
> 2100x1500 for optimum results for 7x5s. Divide your pixels by 300. I
> routinely scan at 4000 ppi input (@ 300 ppi output) because I know I
> can use the images for *every* purpose. If I need a big 18x12, no
> problem. If I need a small image for the website, no problem. If I need
> a 9x6, no problem. However, if I scan too small I'm snookered if I want
> a really big print.
>
> Your images are scanned in at 96 dpi. Just do the maths to make sure
> that the correct number of pixels is present in any image per print
> size before you get your prints done. If film is canned at 300 ppi,
> software can show its dimensions in inches. For example, a recent scan
> of mine is 5557x3640, which when shown in inches is 18.5233x12.1333, so
> I know what maximum print size I can get.
>
> Some consumer labs will produce print sizes in relation to submitted
> image sizes that go way below 300 ppi as a minimum requirement, and
> many are more than happy enough with the results. I can see it though.
> Get below 200 ppi and things start to really go downhill. But it
> doesn't make sense to compromise resolution in this way unless you're
> just after 'happy-snappies', and there's nothing wrong with that, of
> course!
>
> A second point: JPEG compression quality refers to the amount of data
> the software loses when it saves the image. This is why JPEGs are used
> for web pages. In terms of KBs, they can be quite small but still look
> ok. But if you compress too much you'll lose too much data and the
> detail and colour will go out the window. I recommend you set it to the
> very best quality possible, or even better, save your scans as TIFFs
> and convert to a JPEG when you have worked at the image, if that's what
> you intend to do.
>
> "The JPEG standard was written by the committee known as the Joint
> Photographic Experts Group, and it was designed for compressing full
> color or grayscale images (in particular, photographs and similar
> high-quality artwork). JPEG is a 'lossy' file format; when the JPEG
> algorithm compresses the image, it reduces the size by chucking bits of
> the image away. How does it know what to lose? JPEG compression plays
> on the fact that the human eye can only see so much. We have trouble
> seeing small color changes, so JPEG loses some of this subtle
> information" (Una Dooney).
>
> I would express the difference between dpi and ppi like this: "The
> resolution of a digital image is measured in pixels per inch, not dots
> per inch. Software may show the image resolution as DPI, but strictly
> speaking this is not correct. Unfortunately, the two terms - ppi and
> dpi - tend to be used interchangeably, even by some professionals.
> Dpi refers to a printer's output resolution, not the resolution of a
> digital image." There are no "dots" in a digital image, just pixels.
>
> Hope I haven't missed too much. Not too much time at the moment, but
> feel free to email me through the site if you feel I can be of any use.
>
>
> Good luck with those scans!
>
Anonymous
June 25, 2005 5:16:34 PM

Archived from groups: rec.photo.digital (More info?)

"Sharp Shooter" <theimageplane@uk2.net> wrote:

>Hello Terry
>
>It's accepted that an input value of 4000 ppi is best simply because it
>covers all possible uses for the final image and wrings as much
>information as possible from the neg or slide. 4000 ppi is the way to
>go for larger print sizes and detailed editing requirements. 300 ppi
>(it will probably read dpi) is the output resolution for home printers
>and professional digital equipment that produce digital prints.
>
>Each print size requires a minimum number of pixels at 300 ppi
>resolution to ensure the best resolution. Beyond this, the resolution
>is just wasted - you'll never see it. So ideally, a 7x5 print should be
>around 2100x1500 pixels. If you ask too few pixels to fill too big a
>space for a specific print size, the image will start to break up with
>the individual pixels becoming more obvious.
>
>See here: http://www.theimageplane.net/interp.htm
>
>The bad news for you is that the image quality of flatbed film
>attachments fall some way behind dedicated film scanners, so for
>optimum results it's best to use a scanner specifically designed to
>scan 35mm film. However, if you're producing smaller prints, you may
>well find that your scanner will deliver good results if you scan for
>reasonable detail.
>
>Hope this helps.
>
>:o )

Sure does! Much appreciate that prompt and comprehensive reply. Hope
you don't mind a few follow-ups please?

The drop-down list in EPSON SCAN doesn't include 4000, so I've entered
that manually. I've just done a couple of scans with that. Slides were
approx 35 x 25mm. The program's JPG setting was at 'Compression Level
16', whatever that means; in another dialog it's described as '85%
high quality'! That resulted in files of about 1.4 MB. For an exact
comparison, I scanned the same slide twice. Leaving aside the fact
that this 30-year old slide was poor anyway, here's the comparison:

http://www.terrypin.dial.pipex.com/Images/Anthony-Baby-...
1481 KB res = 4000 dpi

http://www.terrypin.dial.pipex.com/Images/Anthony-Baby-...
659 KB res = 2400 dpi

I suppose compression complicates the size ratio? If size was simply
proportional to area and resolution, I'd expect the 4000 version to be
(4000/2400)^2 = 2.78 times larger than the 2400 version, i.e. about
1835 KB, instead of 1481 KB.

I can't personally see any difference on my 1024 x 768 monitor, but I
suppose I would if I made two 5" x 7" prints?

BTW, what exactly does the 'd' in dpi stand for, and why is it shown
as that instead of the unambiguous 'ppi'= pixels per inch?

Will now study that ImagePlane site carefully!

--
Terry, West Sussex, UK
Anonymous
June 25, 2005 5:16:35 PM

Archived from groups: rec.photo.digital (More info?)

Hi Terry:

DPI means "dots per inch" and usually refers to your printer output. It is
independent of the image PPI, or "pixels per inch" I'll usually size my
photos at 300 ppi, and set my printer at 720 dpi.

A couple of other comments:
Your scanner has a maximum optical resolution of 2400 dpi. Above that, it
is interpolating the extra pixels and does not give you more detail or
resolution. Most people will recommend that you scan slides at the maximum
optical resolution and avoid interpolation.
If you're able to save your scans in a lossles format such as TIFF or
Photoshop PSD, you'll avoid getting any jpeg compression artifacts in your
images. Whether they're visible or not depends on the jpeg setting at the
print size. If you have to save in jpeg, use the maximum (least
compression) setting.

regards...
MTB



> Sure does! Much appreciate that prompt and comprehensive reply. Hope
> you don't mind a few follow-ups please?
>
> The drop-down list in EPSON SCAN doesn't include 4000, so I've entered
> that manually. I've just done a couple of scans with that. Slides were
> approx 35 x 25mm. The program's JPG setting was at 'Compression Level
> 16', whatever that means; in another dialog it's described as '85%
> high quality'! That resulted in files of about 1.4 MB. For an exact
> comparison, I scanned the same slide twice. Leaving aside the fact
> that this 30-year old slide was poor anyway, here's the comparison:
>
> http://www.terrypin.dial.pipex.com/Images/Anthony-Baby-...
> 1481 KB res = 4000 dpi
>
> http://www.terrypin.dial.pipex.com/Images/Anthony-Baby-...
> 659 KB res = 2400 dpi
>
> I suppose compression complicates the size ratio? If size was simply
> proportional to area and resolution, I'd expect the 4000 version to be
> (4000/2400)^2 = 2.78 times larger than the 2400 version, i.e. about
> 1835 KB, instead of 1481 KB.
>
> I can't personally see any difference on my 1024 x 768 monitor, but I
> suppose I would if I made two 5" x 7" prints?
>
> BTW, what exactly does the 'd' in dpi stand for, and why is it shown
> as that instead of the unambiguous 'ppi'= pixels per inch?
>
> Will now study that ImagePlane site carefully!
>
> --
> Terry, West Sussex, UK
>
Anonymous
June 25, 2005 7:27:41 PM

Archived from groups: rec.photo.digital (More info?)

"Sharp Shooter" <theimageplane@uk2.net> wrote:

>Hello Terry
>
>I would think your scans would produce prints you'll be delighted with.
>It won't be in the same league as dedicated film scanners, but judging
>by these scans it will do a really good job! A flatbed scanner won't
>compete with a film scanner resolution wise, but scan at the best
>resolution you can without any digital trickery (the adding of pixels).
>
>But there are a couple of issues here:
>
>Firstly, if you're sure you will not be needing very large prints, scan
>at a resolution that will deliver the best print results, as we
>discussed above - 300 dpi (ppi) is the norm with film scanners. Or, to
>put it another way, it wouldn't make sense to scan at a 2400 dpi input
>value if you're only wanting 7x5 prints. The maths here works out at
>2100x1500 for optimum results for 7x5s. Divide your pixels by 300. I
>routinely scan at 4000 ppi input (@ 300 ppi output) because I know I
>can use the images for *every* purpose. If I need a big 18x12, no
>problem. If I need a small image for the website, no problem. If I need
>a 9x6, no problem. However, if I scan too small I'm snookered if I want
>a really big print.
>
>Your images are scanned in at 96 dpi. Just do the maths to make sure
>that the correct number of pixels is present in any image per print
>size before you get your prints done. If film is canned at 300 ppi,
>software can show its dimensions in inches. For example, a recent scan
>of mine is 5557x3640, which when shown in inches is 18.5233x12.1333, so
>I know what maximum print size I can get.
>
>Some consumer labs will produce print sizes in relation to submitted
>image sizes that go way below 300 ppi as a minimum requirement, and
>many are more than happy enough with the results. I can see it though.
>Get below 200 ppi and things start to really go downhill. But it
>doesn't make sense to compromise resolution in this way unless you're
>just after 'happy-snappies', and there's nothing wrong with that, of
>course!
>
>A second point: JPEG compression quality refers to the amount of data
>the software loses when it saves the image. This is why JPEGs are used
>for web pages. In terms of KBs, they can be quite small but still look
>ok. But if you compress too much you'll lose too much data and the
>detail and colour will go out the window. I recommend you set it to the
>very best quality possible, or even better, save your scans as TIFFs
>and convert to a JPEG when you have worked at the image, if that's what
>you intend to do.
>
>"The JPEG standard was written by the committee known as the Joint
>Photographic Experts Group, and it was designed for compressing full
>color or grayscale images (in particular, photographs and similar
>high-quality artwork). JPEG is a 'lossy' file format; when the JPEG
>algorithm compresses the image, it reduces the size by chucking bits of
>the image away. How does it know what to lose? JPEG compression plays
>on the fact that the human eye can only see so much. We have trouble
>seeing small color changes, so JPEG loses some of this subtle
>information" (Una Dooney).
>
>I would express the difference between dpi and ppi like this: "The
>resolution of a digital image is measured in pixels per inch, not dots
>per inch. Software may show the image resolution as DPI, but strictly
>speaking this is not correct. Unfortunately, the two terms - ppi and
>dpi - tend to be used interchangeably, even by some professionals.
>Dpi refers to a printer's output resolution, not the resolution of a
>digital image." There are no "dots" in a digital image, just pixels.
>
>Hope I haven't missed too much. Not too much time at the moment, but
>feel free to email me through the site if you feel I can be of any use.
>
>
>Good luck with those scans!

Thanks both, very helpful.

I'm going to have to get stuck in tomorrow to really get a grasp of
this. I confess that at the moment I'm floundering, but that's partly
because of unfamiliarity with this software. My crude test of any
trial is to view it on my screen, so printing and print sizes don't
figure much in my thinking. And my simplistic reasoning was simply
that, as the source is so small (1" x 1.5"), I have to scale up the
resolution proportionally. 2400 seems to work OK. But, as I say, I've
plainly got a lot of basic studying to do!

Husband duties now call, but back on the case tomorrow afternoon <g>.

--
Terry, West Sussex, UK
!