scanning photos for printing

[Roberto]

I just noticed the recent post on "DPI for photo quality" and have a similar question. I have a 600x1200 scanner and a 300dpi ink-jet printer. I would like to scan some 4x6 photos and print them at that size or larger while maintaining as much quality as possible.

What scan resolution should I use? What is the conversion from scan resolution to printer dpi?

[Charliey]

Is there anything in the scanner settings that let you chose the dpi? dpi on a scanner as dpi is on a printer. If you want to enlarge it, you should scan it with a bit more dpi, like 400-500 depending on how much you want to enlarge it.

[Sandgroper]

300 DPI is the absolute minimum resolution to get near photo quality prints at the standard 6 x 4 size on home gear. If your printer software has it, switch on the image optimiser. Set printer quality to the finest you can and use the best quality gloss photopaper you can afford. Increase to 32 bit colour in display properties. Try scanning at 300 DPI into your imaging software then "fit to page" in print preview and test print. If your printer is up to it you may get a passable result. If you do, you will obviously get better results at smaller sizes. If not you will need to get a printer that can handle at least 600 DPI, particularly if you want to enlarge to A4.If you use the largest DPI you have on the scanner, I hope you have alot of RAM, a fast CPU and big fast video card, otherwise manipulation can be a painfully slow experience. After all this, you can get adequate repro at 200 DPI if you have a newer "photo" type printer. All the top names (Epson, HP, Canon etc)all have "photo" settings that produce passable results from quite low resolutions. Down load the latest driver from your scanner and printer maker. The one that comes on the installation disc or Windows is very often about three revisions behind and this can make a big difference. Good imaging software can make things easier also. I use PhotoImpact V6, it's pretty good, Paint Shop Pro is OK but not as intuitive.
http://www.shortcourses.com has good background info about scanning, digi photography and printing, our site is http://www.kaistech.iinet.net.au and may give you some inspiration.

[slipe]

Hey Roberto:

You are ahead of most folks in that you know the difference. I think most older 300 DPI inkjets use 7 or 8 dots per pixel. You could just be conservative and multiply the scanner DPI by 6. So if you scan at 200 DPI that is at least 1200 DPI of printer resolution. Some people use pixels per inch (PPI) instead of DPI to differentiate the two.

Most newer high resolution printers use much smaller dots and have at least 11 dots per pixel. On the HP printer forum there is always someone complaining that he or she scanned their image at some extreme resolution and Photoshop comes up with a little box when you print saying it is sending the image to the printer at 300 DPI. So they have a 1200 X 2400 DPI printer and Photoshop will only send a measly 300 DPI. Actually, with at least 11 dots per pixel the PRINTER resolution it is sending is over 3000 DPI and the print spooler is going to have to downsample the file to print it. http://scantips.com/basics03.html

There is no more than 200 scanner DPI or PPI on a good photograph. If you follow the links to his test example, Wayne Fulton uses a photo he took with a fixed Nikon 50mm lens on a tripod to demonstrate the point. He also provides some good references: http://scantips.com/basics08.html

If I am going to print on photo paper at 1200 X 2400 I scan at 300 DPI even though it will not improve detail over 200. I do that for several reasons. The printer instructions suggest 300 DPI scans for printing at best quality on photo paper so it can downsample the image rather than upsample it. If I want to blow the image up in Photoshop to enhance it I have more pixels to work with even though it is no sharper. I also have 512 Mg RAM so I can be a little cavalier about image size.

You can’t go wrong scanning at 200 DPI for your printer. You get all the detail available on the photo and your printer driver will definitely have to downsample as there will be more pixels than it can use.

If you want to print the photo larger than the print you scanned there are a couple of ways to do that. Be aware that quality will suffer a little as there is not enough information on a print to make a really good quality blow up no matter what equipment you have.
The first way is to set the size you want in the scanner software. Most image editing software will print at the size the scanner sends it if you don’t change anything. Be aware that if you scan a 4 X 5 print with the size set to 8 X 10 and the resolution at 200 DPI, the scanner will actually scan the photo at 400 DPI which is excessive. I would set the scanner for no more than 150 DPI in this case giving you a 300 DPI scan.
The second way is to scan the photo at regular size and have the image editing software resize it to the print size you want. In Photoshop you have a choice between resampling to a desired print size or to a size in pixels. You want the print size.
If your editing software has the option, you could also set it to “fit to page” as Sandgrouper suggests. This gives you the largest print size your paper will allow. http://www.scantips.com/basics02.html

[Roberto]

What a great bunch of tips from everyone. It will take me a while to follow through on all the links.

Thanks a million.