Hello, I have a question regarding scanning slides for an eventual printing in 24 x 16" as maximum. I use the Nikon coolscan 50, 4000 dpi and 8 bit color depth. The resulting files are about 22 MB in JPEG format, and the size of the scanned image is 24 x 36 mm. First question: why are the files so big? Second: how should I resize the image in photoshop in order to enlarge the 24 x 36 mm to 16 x 24" keeping the enough resolution to print it? Thrid: how can I have the same image in a smaller file, still keeping the right resolution for later printing?
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#1. "RE: Scanning Slides" | In response to Reply # 0blw Nikonian since 18th Jun 2004Tue 26-Apr-11 09:09 PM
I don't routinely work in JPEG, but I do know that 3200 dpi scans into roughly a 12mp image. So 4000 dpi gives you roughly a 16mp image. Since JPEG uses compression, a larger file tends to mean more detail, which in this case could be real detail or just scanning of the grain.
If your original capture was done with fine grain film, good glass and technique, you should have no problem printing this at 16x24. But if you pushed Tri-X to 1600, used mediocre glass, or had some technique issues, 16x24 will not look very good.
When I've printed this kind of stuff I have usually scanned at 3200 dpi (my scanner doesn't have a 4000 dpi option) and then did a normal image-image_size -> bicubic sharper. That is certainly sufficient for 12mp digital captures at even larger print sizes. If this is critical, you might invest in one of the resizer programs such as Genuine Fractals or QImage, and let them do the magic.
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#2. "RE: Scanning Slides" | In response to Reply # 0
I think you'll have to decide what is more important to you - file size or resolution/scanned image quality. If you are looking to truly archive these photos in the digital realm and/or you want to make high quality large format prints I think you need to scan at the native resolution of the scanner, at 16-bit color (actually 12-bit with Nikon Coolscans but read as 16-bit by Photoshop), and save as TIF files, not JPGs. Once they are digitized at the highest quality you can then manipulate these image files to suit your intended output. Now, if you just want to digitize them for small prints or sharing on the web and e-mail then you can reduce the scan settings to 8-bit, and 1,500 to 2,000 ppi. Whatever you decide you will have to accept that the files will be rather big.
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#3. "RE: Scanning Slides" | In response to Reply # 2Wed 11-May-11 02:41 PM
Thanks Ernesto, I find your suggestions very useful. probably I'll scan them in 16 bit depth and as TIF files, then I'll decide at the moment of printing. Yes, the 16 bit scan produces 52 MB files for each slide!!
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