dpi?

[bunzino]

Hi all,

I remember a discussion (not sure if it was here) where folks said they scanned at 600 dpi if they were printing a book. My question is probably quite dumb, but let's say you take a picture w a certain camera. Can you really get MORE or BETTER detail/resolution depending on how you scan it?

Seems to me you can't create what is not already there.

Hope I'm making sense :-)

Nina

[CarolLHB]

I'm nooooo expert, Nina, but my understanding is that you get more pixels (data) per inch so that you have lots to work with as you edit. I really only scan at that setting if i am restoring a photo. Hope this helps, I am sure someone way more knowledgeable will be along:)

[GaryK]

Hi Nina

You are right, you can't add what is not there... at least not reliably.:)

Just for fun though, try scanning a photo of a face at 3 different resolutions.(150, 300, 600 or low medium high)

Open each in elements and then set to tile or cascade mode.

Zoom in on an eye and make each roughly the same screen size.. see the difference?
If the photo is in relatively good shape there should be a huge difference in the jagginess of the pupil/whites.

Now, you aren't adding anything, and I would imagine that at some point, or at least on a very small photo there will be negligible difference but there is a difference.

I don't really know where I am going with this .. just give it a try.:D

[Juergen D]

Nina,
Here is some information on scanning and resolution (it's really PPI, not DPI, another story :) ) :
http://www.scantips.com/

Juergen

[lotzaquestions]

Re: scanning and resolution, my scanner offers me the choice of several resolutions. The default is 200, but I select 300 because most people seem to think that is a good one to use. My question is this; why does my scanner offer settings ranging from 95 ppi all the way up to 19200. Just for the heck of it, I scanned a picture at 200 and one at 3600 and the difference is barely visible. The only real difference is the file size, which is humungous. Why would my scanner offer these huge options if they don't do anything but make the file large?

While on the subject of scanning, let me also ask this. My scanner has the option of setting color, size, sharpening, etc etc. Would it be better to use the scanner's software to make the corrections and then tweak them in PSE5 or just scan them at the default settings and do the editing in PSE5 as I have been doing all along.
TIA
Barbara
TIA

[Wendy]

hi Barbara ...

I tend to scan as it is and do correction in Elements ..

Now about the scanners having all those options, I supect that the answer is some people need them for various things they do and its probably no more expensive to provide them.

Its a bit like settings on the washing machine ... mine has lots but I only use three :D :D

Wendy

[Codebreaker]

There is no optimum resolution for scanning. These questions must always be asked -

What am I going to do with the end results - print or display on screen?
If printing what size?
If displaying what screen resolution?

Once you know the answers to these you can work out what scanning resolution you need to get enough pixels onto the print or on the screen.

In the end scanning is about getting enough pixels into the image for the purpose intended.

Colin

[Juergen D]

One thing to keep in mind is the size of the original. If scanning a 35mm slide, to be printed at 6 x 4, 1200 PPI would be appropriate. If scanning a 6 x 4, which is to be printed at its original size, 300 PPI would be sufficient.
http://www.image-access.net/calc/index.html

Juergen

[cats4jan]

Its a bit like settings on the washing machine ... mine has lots but I only use three

I only use one - I only bought the fancy machine because you can't get second rinse on the lower end machines.

And my dryer? I always use "timed"

And my dishwasher? One setting.

Guess I'm ready for the low-tech life - except with computers - there I want

MORE MORE MORE

Alright, I'm done -

Went off on a strange useless tangent

It's Monday morning - what do you expect?

[tomlaronge]

Nina,
I echo Wendy, Colin and Gary. However, please keep in mind that resolution is only a very small part of the end product quality. For example, one of the best known manufacturer of high quality, dedicated scanners makes a high end product that can scan at very high dpi, but it has a mediocre optical system. Some scanners at half its price produce far better results.
Another consideration relates to the scanner source material and the scanner software. Native scan resolution can be largely upset by optical aberratioons including reflections, color temperature shifts, etc.
So, I recommend going back to the Kiss Principle. Kepp all equipment and surfaces clean and as free from scratches and other marks as is possible. Scan a desired item at the largest possible resolution in dpi and preferable as a TIFF or PSD, Do your editing in Elements or other editing software. Print the scan at the resolution recommended for use in the final product, i.e. about 72ppi for use on the Internet, up to about 96ppi for use on an average LCD screen, about 240ppi for use on an Epson printed document, about 300ppi on a Canon printed document, etc., etc., etc.
The rule of thumb is to use only one item, hardware or software, to do one specific task to avoid conflicts and complications.
Finally, Nina, this is not the total story as you can, depending upon available equipment, skill level and software, scan at 8bit, 10bit, 12bit, 16bit, 24bit, 32bit, 48bit, etc. The different bit rate capacities may dramatically affects the quality of a high resolution, well edited, well printed final broduct where the color differences can be resolved by the viewer.
I have probably left out a lot, but KISS will bring the utility of scanning back into your very own control. Have fun scanning.
Tom

[GaryK]

Barbara

If you still have your two scans, I suggest bringing them both into elements and blowing them up.

As I mentioned to Nina, if it is a face pick the eyeball, and make it as big as you can with both still visible on the screen. Or pick a leaf/petal what have you.

I would be very surprised it you couldn't see the difference.

[Codebreaker]

Tom....

While I think the principles you mention are good maybe you've made things a little too simple and problems could occur if some of your suggestions are used.

The resolutions you quote for printers would only yield an adequate scan for printing at 1:1. If you need to enlarge a scan then the resolution has to increase. This is particularly relavent when scanning negatives or slides for which prints are required.

There is no need for different settings between the Internet and Displays - after all you can only view Internet content on a Display.

Colin

[NickLewis]

I'll have a go at this one, for my sins.

The important thing to know is what you're going to do with the finished output, and use that information to calculate the pixel dimensions that you need your image to have. Note I said the pixel dimensions, not the resolution (ppi). You'll lead yourself up the garden path if you fixate on resolution as a magic number. You need to understand properly how it fits in.

And particularly you need to make a break in your mind between the scanning resolution, and the resolution of the finished product. As Colin said, they are only the same if you are producing a 1:1 copy of the original in the same medium, which is very often not the case.

If you're targeting some sort of screen display, forget its resolution. The numbers that get bandied about (Usually 72 or 96 ppi) are complete red herrings, rooted in history. The monitor I'm typing this on at the moment is a 17", running at 1280x1024 pixels. That happens to have a resolution of 96 ppi, but if I reset it to 1024 x 768, it would be about 77 ppi. And if I was running 1024x768 on my laptop screen, the resolution is 85 ppi, because the screen is smaller. So for a display, forget ppi, and think directly about how many pixels you need - perhaps you want an 800x600 image, to comfortably fill a 1024x768 web page.

If you're aiming to print something on a domestic inkjet printer then you need to involve the print resolution. You need to send the printer an image with about 250 ppi for photographic quality. (Don't confuse pixels per inch (ppi) which is related to the image file, with dots per inch (dpi), which is to do with the number of ink dots the printer lays on your paper, and is higher.)

So the next question is: how big will your print be? If you're going to print a 10"x8", then the image you send the printer will need to be about 2500x2000 pixels. (10"x250ppi=2500pixels) About 5 million pixels in all. So, if you were scanning a 6x4, you'd have to scan it at a scanning resolution of 2500/6=416 ppi or higher. (Assuming that the print had that much resolution to start with, which it probably wouldn't if it was an inkjet itself, for example.)

But if you were scanning a 35mm film frame to print this way, the frame is 1.5"x1" (roughly), so you'd have to scan at 2500/1.5=1700 ppi.

But if I was scanning a 6x4 to put up on the web, as an 800x600 image, I'd only need 800/6=133 ppi.

All of that assumes that you are going to print the whole image. If you're going to crop half of it out, you'll need more pixels to start with.

So work out what you'll need eventually, and then scan accordingly.

There's one final wrinkle. Don't scan at a resolution higher than the native optical resolution of your scanner. All that then happens is that your scanner software interpolates the extra pixels. (Interpolate= a mathematically based guess). If you really must interpolate pixels, you are almost certainly better off doing it in PSE. And if you scan at a lower resolution than your scanner's optical quality, then do it at a resolution that is a binary sub-multiple of that (i.e. divided by a power of two). So if the scanner can do 1200 ppi, scan at 600 or 300. This minimises the amount of interpolation that the scanner software will get up to.

I know this sounds complex, but it is actually only simple multiplication and division of a few numbers. It is worth trying to understand why you're doing what you're doing, because it will be a lot simpler and more reliable once you do.

Nick

P.S. I know I've played fast and loose with the changing aspect ratios of my examples, for the sake of simplicity. If you have spotted that, you've understood what's going on!

[Juergen D]

I know this sounds complex, but it is actually only simple multiplication and division of a few numbers.
Nick,
That is a very good write-up on the subject! I had posted the link earlier already, but here is the Scanning Resolution Calculator one more time:
http://www.image-access.net/calc/index.html

Juergen

[JulieM]

Nick: Thank you so much for providing that excellent explanation. I think I've got it now!

Juergen: Thanks for the calculator link. I only wish it had a 4x6 in option for the original. That would seem to me to be a frequently scanned size. I think I'll make an excel spreadsheet to do the task for this.

[NickLewis]

No problem.

I think you'll be fine with Juergen's link. The difference between 5x4 and 6x4 is unlikely to matter much. Don't get hung up on scanning at the exact resolution suggested by calculation. as you'll need to be rounding up to the next suitable scanner resolution anyway.

On the other hand, writing a spreadsheet is a useful way of confirming you've grasped the principles.:)

Nick

[CarolLHB]

That's what I love about this place...ask a simple question, get a simple answer:D:D

Thanks so much for all the info-it really hepled my understanding:)

[tomlaronge]

Colin,
I agree with what you stated and I thank you for pointing this out.

Nick,
What you wrote is very true and i totally agree. However, I still caution that when scanning, hardware quality and alignment is often a major contributor to the quality or lack there of in the results. Many scanners, even some expensive ones, do not use sufficient quality optics, etc. to produce sharp images regardless of the scanning resolution.
Tom

[bunzino]

A HUGE thank you to everyone for their input on my "stupid" question :-) Evidently I wasn't the only one wondering..........

The calculator is great, and all the other suggestions really helped me w this issue which I'd never before really gotten into my head.

Thanks again - what a great group of folks!!

Nina

[NickLewis]

Nick,
What you wrote is very true and i totally agree. However, I still caution that when scanning, hardware quality and alignment is often a major contributor to the quality or lack there of in the results. Many scanners, even some expensive ones, do not use sufficient quality optics, etc. to produce sharp images regardless of the scanning resolution.
TomI entirely agree, but there's very little most people can do about that, except be careful in their original purchase.

Meanwhile, many, many people are completely bemused about what to do over the resolution issue, so they either end up with files which are far larger than they need be, or pixelated output.:(

Nick