I am using a Polaroid Sprinscan 4000, and an Epson Photo 1270. The printer has a maximum resolution of 1440 dpi. Therefore (I thought!) I scanned at a resolution to closely match that - 1500 dpi yeilding about an 8mb file from my slide. When I go to print, I increase the size to, say, 8x12 and interpolate the image down to 240 dpi. However, I still get jagged pixelated edges. Is the ideal thing to scan at the max resolution of 4000 dpi (read: slow) and then interpolate? I guess I am just after the best resolution to scan my slides at for the best reults on this printer. Is an image interpolated from 4000 dpi the same as one scanned and interpolated from 1500? I am a beginner, so thanks for taking the time to read.

-- Michael Smith (rocksnowsky@earthlink.net), August 17, 2000

Answers

I'm going to try really hard to keep this short and simple. I'm already sleepy and afraid of boring myself to sleep as well as you. :-)

1440 DPI does not always equal 1440 PPI...

Printer manufacturers use DPI(Dots Per Inch) to specify the resolution of their print engines. When imaging you're talking about PPI(Pixels Per Inch). The difference is that a printer dot can only be a single ink's color, whereas a pixel can be any shade out of the whole gamut of colors you're working with. Generally, a pixel can be any color out of 16.7 milllion for 24 bit color depth. Your printer uses a number of it's smaller single colored ink dots, in varying sizes, to help form the shade of each pixel.

In general you should print at 240 to 360 PPI(some programs may use the term DPI), with 300PPI being the proper, middle of the road, yet "Looks super!" setting...

Don't interpolate, just change the resolution setting from 72PPI to 300PPI or whatever PPI you need to get the image size you want and make sure the "resample" box is not checked. Let the printer driver do the interpolation, or scan to get an image size that when divided by the PPI you're printing at will yield the proper image dimensions.

Simple rule: Image resolution / Printing resolution = Size

All in pixels and inches, and Pixels Per Inch...

Example: 4000 pixels / 300 PPI = 13.33 inches!

Which means an image 4000 pixels across(up and down, whichever) can be printed as large as 13.33" @ 300PPI!

If you actually scan a 35mm image at 4000PPI, you should get

35mm / 25.4mm(per inch) X 4000PPI = 5512 pixels

and

5512 / 300 PPI = 18.37" length printed @ 300 PPI

You can, of course, scan at a lower resolution or print at a higher resolution to get smaller prints. The smart approach is scanning at a higher res. for things you may one day need to blow up large, and at a lower res. for small prints. If you're archiving, scan at the higher res. The nice thing about lower res. scans is that they take up less disk space. The unfortunate part is they also contain less resolution and can't be printed as large.

Interpolating down to a smaller size is usually fine, interpolating up does little for you since you're not creating detail, just pixels.

phew! I hope that covers most of the bases. Good luck!

-- Gerald M. Payne (gmp@surferz.net), August 17, 2000.

Gerald, this was excellent. Could you do something similar on "Genuine Fractals" ?

-- Tom Muhlstein (tom.muhlstein@sympatico.ca), August 17, 2000.

Genuine Fractals will not help at all in the current situation here, essentially Genuine Fractals allows you to interpolate an image to a higher pixel count using a different and I think higher quality method than photoshop. I the case of the original topic here, Michael has the right equipment, its just the whole resolution topic that can throw people. Think of resolution as "light bright", that little toy that kids put the pegs in and they glow. Thats how I often try to explain resolution without getting to mathematical. If your light bright picture has 10 pegs across by 10 pegs down, each peg seperated by .5", the image you see would be approximately 5 inches by 5 inches or 2 pegs per inch. Now our "resolution" of 10 pegs by 10 pegs = 100 pegs. If I move the pegs closer together, say to .25", our new image would appear 2.5" x 2.5" or 4 pegs per inch. That essentially is our print size, 2.5" x 2.5" @ 4ppi. Now there are still 100 pegs no matter how you cut it, I'm just moving them closer or farther apart from eachother. The accepted standard as mentioned before is around 300 ppi. Genuine Fractals will create some "intermediate virtual pegs" (I kinda like that...)should we need some more file size to create a larger print ,but theres nothing like the real thing and Genuine Fractals cant work miracles. So there it is, now go get your kids "Light Brite" and get crackin'......

-- Cris Daniels (danfla@gte.net), August 17, 2000.

Sorry Tom, most of what I know concerning Genuine Fractals comes from the Imaging Resource Article found on www.imaging-resource.com . I don't have a copy and just haven't used it yet. The rest of what I know involves more concerning fractals and math in general than the program. And really constitutes precious little -I just never got that interested in playing around with or programming anything having to do with fractals.

The last time I did any reading they were talking about fractals being built out of scalable triangles... if that's any help, it was my pleasure... :-)

-- Gerald M. Payne (gmp@surferz.net), August 17, 2000.