[Joseph Henry]

Hi,
I just bought an Epson 1650 Photo scanner that I am using to scan my grand parents old slides (I want to get them all on CD). Right now I am scanning at 600 dpi with a target image size of around a 4X6 print. Thinking ahead, though, I may want to enlarge the photo's even further to like 5x7 or 8x10. If I increase the resolution (to perhaps 1600 dpi) but keep the target size at 4x6 can I then later take that photo and enlarge it and still get good quality? I want to keep the 4x6 target size because that's the size I usually print. I am totally new at this scanning stuff (as if you couln't already tell) so any advice would be greatly appreciated.


[ 03-28-2002: Message edited by: Joseph Henry ]

[CarpetFluff]

I'm a bit rusty on scanning but I'll have a go at answering your question.

By the target size I presume you mean the print size, this size is irrelevant. The scanner you bought has a maximum optical resolution that it can scan an image or slide at. If you're scanning at a scale of 100% at the maximum optical resolution then you are getting the best quality image you possibly can from the scanner.

So scanning your image at 1600dpi (which I think is the maximum optical resolution for that scanner) at 100% scale will produce the best result, but it may be a very large file. If you're scanning 35mm slides then this would be best as the source image is so tiny that you need all the resolution you can get.

You can also enlarge an image to a higher resolution using interpolation. This is where the computer puts in extra pixels based on the information in the pixels that are already there, it's to be avoided where possible though as it gives you a poorer quality image. Any settings you see on your scanner that go larger than the optical resolution are interpolated, you won't get any better quality you'll just get a larger file size. If you have to interpolate an image (otherwise known as resampling) then you should always use an image editing application to do this as it's likely to give you better results than the scanner, so scan at the maximum optical resolution, bring it in to Photoshop and enlarge.

Understanding and learning how to use the IMAGE SIZE box in Photoshop would really help you out, i'm sure there are tons of tutorials on this on the web if you go looking.

Anyway, I hope that was useful I'm not the worlds best when it comes to explaining things

[SimeyTheLimey]

Originally posted by Joseph Henry:
<STRONG>Hi,
I just bought an Epson 1650 Photo scanner that I am using to scan my grand parents old slides (I want to get them all on CD). Right now I am scanning at 600 dpi with a target image size of around a 4X6 print. Thinking ahead, though, I may want to enlarge the photo's even further to like 5x7 or 8x10. If I increase the resolution (to perhaps 1600 dpi) but keep the target size at 4x6 can I then later take that photo and enlarge it and still get good quality? I want to keep the 4x6 target size because that's the size I usually print. I am totally new at this scanning stuff (as if you couln't already tell) so any advice would be greatly appreciated.


[ 03-28-2002: Message edited by: Joseph Henry ]</STRONG>

It's usually best to scan at 100%, then resize in photoshop. If you resize first you will get a nasty case of the jaggies.

Reviews I have seen of that scanner suggest that 8x10 is probably really pushing it from a 35mm slide. But for medium format or 4x5 slides it's supposed to be pretty good for a flatbed.

If you do a lot of slide scanning, you might want to consider a dedicated film scanner.

[Joseph Henry]

Thanks CarpetFluff and Limey for the replies, I think (hope) that I am starting to get it. I have another newbie question, however. What is the relationship (if there is one) between dpi/resolution and ppi (pixels per inch) which is what my Kodak DC290 uses to measure picture size. For instance, at the High resolution setting on my camera, the manual states that the picture size is 1792x1200 pixels.

[SimeyTheLimey]

Originally posted by Joseph Henry:
<STRONG>Thanks CarpetFluff and Limey for the replies, I think (hope) that I am starting to get it. I have another newbie question, however. What is the relationship (if there is one) between dpi/resolution and ppi (pixels per inch) which is what my Kodak DC290 uses to measure picture size. For instance, at the High resolution setting on my camera, the manual states that the picture size is 1792x1200 pixels.

</STRONG>

I'll offer a guess. I think dpi is printer resolution and ppi is what your camera resolves. I think also the specification of your camera's chip necessarily overstates the actual resolution by 3x because you have to have three receptors for one pixel of color image (one red, one green, and one blue).

Another possibility is that they are just telling you the size if you viewed it at 100%. In reality, you'd reduce.

Having said that, my background is in conventional photography and I just got spanked on the Leica Users Group for misapplying these kind of terms.

I'm comfortable enough using the stuff, but I find the technical details of digital cameras relatively arcane and unrelated to actual use. That's particularly so because the manufacturers themselves often seem to spin the specifications for marketing reasons (e.g. interpolated resolution, etc) making them often useless for real comparative purposes.

The lesson I take is just use it and doen't sweat what's written in the brochure.

[OldManMac]

Click here for scan tips and good information.

[Joseph Henry]

Thanks karlG! Every thing I wanted to know and more!

Joe