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

Question

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.

Answer 1

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.