I would appreciate it if someone could advise me as to the optimum resolution, dimensions and dpi for actual photographic slides that I am scanning for use in a Keynote Presentation, that will be projected in a large auditorium. I realize that most proje

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I would appreciate it if someone could advise me as to the optimum resolution, dimensions and dpi for actual photographic slides that I am scanning for use in a Keynote Presentation, that will be projected in a large auditorium. I realize that most proje

I would appreciate it if someone could advise me as to the optimum resolution, dimensions and dpi for actual photographic slides that I am scanning for use in a Keynote Presentation, that will be projected in a large auditorium. I realize that most projectors in auditoriums that I will be using have 1024 x 1200 pixels, and possibly 1600 x 1200. There is no reference to this issue in the Keynote Tutorial supplied by Apple, and I have never found a definitive answer to this issue online (although there may be one).

Here’s my question: When scanning my photographic slides, what setting, from 72 dpi to 300 dpi, would result in the best image quality and use up the most efficient amount of space?

Here’s what two different photo slide scanning service suppliers have told me:

Supplier No. 1 tells me that they can scan slides to a size of 1544 x 1024 pixels, at 72 dpi, which will be 763 KB, and they refer to this as low resolution (a JPEG). However, I noticed when I looked at these scanned slides, the size of the slides varied, with a maximum of 1.8 MB. This supplier says that the dpi doesn’t matter when it comes to the quality of the final digital image, that it is the dimensions that matter. They say that if they scanned a slide to a higher resolution (2048 x 3072), they would still scan it at 72 dpi.
Supplier No. 2: They tell me that in order to have a high quality image made from a photographic slide (starting with a 35 mm slide, in all cases), I need to have a “1280 pixel dimension slide, a JPEG, at 300 dpi, that is 8 MB per image.” However, this supplier also offers, on its list of services, a “Standard Resolution JPEG (4MB file/image – 3088 x 2048), as well as a “High Resolution JPEG (8 MB file/image – 3088x2048).
I will be presenting my Keynotes with my MacBook Pro, and will not have a chance to try out the presentations in advance, since the lecture location is far from my home, so that is not an option.
I do not want to use up more memory than necessary on my laptop. I also want to have the best quality image.
One more question: When scanning images myself, on my own scanner, for my Keynote presentations, would I be better off scanning them as JPEGs or TIFFs? I have been told that a TIFF is better because it is less compressed.

Any enlightenment on this subject would be appreciated.

Thank you.

MacBook Pro, Mac OS X (10.5.4), 2 GB 667 MHz DDR2 SDRAM

Posted on Nov 1, 2012 5:14 AM

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Answer 1

Best reply

Gary Scotland

Level 7

25,856 points

Nov 1, 2012 4:14 PM in response to restlesstraveler

Scan to produce an image that are the same as the pixel dimensions of the projector or display screen.

so if you have a 1600 x 1200px monitor you will scan to produce a 1600 x 1200px image

If your have a 1024 x 768px projector, scan to produce a 1024 x 768px image.

Always scan as TIFF, jpeg are highly compressed images and much inferior for use in projection.

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Answer 2

Nov 2, 2012 2:41 AM in response to Gary Scotland

Thanks for taking the time to respond. I just spoke to someone whose business involves scanning slides, and he said that it is best to scan as jpegs, that it used to be the case that jpeg were highly compressed and much inferior, but that is no longer the case. Any more insight to offer on this issue? Thank you very much.

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Answer 3

Nov 2, 2012 1:18 PM in response to restlesstraveler

The whole point of using JPEG images is to produce as small a file size as possible and trying to maintain a decent level of resolution. Saying that JPEGs were once highly compressed and now are not highly compressed is bunkum. The same algorithms are in place today as were when they were last updated 20 years ago.

JPEG images are wondrous things, they are fed image data, squeeze it down to a small size throwing most of the data away and produce a recognisable image out the other side. This is fantastic for low cost camera capture and throwing images on a web page. Its not in any way shape or form the better way of capturing high quality images maintaining colour fidelity. That is the job of TIFF which was specifically invented by software developers to store pristine images from scanners.

In photography, you use the tools available wisely choosing the right one at the right ocasion based on practical experience.

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Answer 4

Nov 7, 2012 8:23 AM in response to restlesstraveler

Scanning is a really complex process, involving not just the scanner settings, but what happens to the image file after you scan. Here are a series of articles which address the subject:

http://dpsdave.hubpages.com/hub/What-makes-a-high-quality-photograph-scan

Let me know what you think!

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Answer 5

Nov 7, 2012 9:38 AM in response to Oregon_Fam_55

This web page gives basic information on scanning but doesnt address the original question:

When scanning my photographic slides, what setting, from 72 dpi to 300 dpi, would result in the best image quality and use up the most efficient amount of space?

the answer is to scan at the dimentions of the out put device in pixels.

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Answer 6

mbasse

Level 1

0 points

Nov 7, 2012 12:54 PM in response to restlesstraveler

When it comes to Keynote, I try and start with a presentation that's 1680 x 1050 preset or something in that range. Most projectors that you'll get at a conference won't project much higher than that and if they run at a lower resolution, it's better to have the device downsize your Keynote. Anything is better than having the projector try and upsize your presentation... you work hard to make it look good, and it's mangled by some tired Epson projector.

As far as slides go, scan them in at 150 dpi or better, and make them at least the dimensions of your presentation. Keynote is really only wanting 72dpi, but I do them at 150, just in case I need to print out the presentation as a handout later, and having the pix at 150 dpi gives me a little help with their quality on a printer.

You'd probably have to drop in the 150 versions again if you output the Keynote to .pdf or Word or something, but at least you have the option.

And Gary's right (above) go ahead and scan them as TIFFs. Sooner or later you'll want to do something else with these slides (like make something for an iPad or the like) and having them as TIFFs keeps your presentation looking good.

Finally, and this is a big one, get to the location for your presentation ahead of time if you can, and plug the laptop in and see what you get. There's always connection problems. Don't let the AV bonehead tell you everything will work just fine ('... I don't have any adapters for a Mac...') . See it for yourself... you're the one that's standing up there. Unless it's your boss, then you better be really sure it works.

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