Very basic scanning question

[Don Wallace]

Sorry if this is simplistic but I can't seem to find basic scanning formulae. Can someone direct me to a good, simple, straightforward page on this? Here is the question: at what resolution should I scan 4x5 (in this case, reversal) to produce an 8x10 print? Is there a formula for scanning different formats for different size prints?

[Michael Mutmansky]

Don,

It comes down to what resolution you want/need the final output to be at.

Most people who use Epson printers use 360 PPI as the output resolution to the printer. If that is the case, and you are scanning a 4x5, then you will need 720 SPI when scanning to produce 360 PPI at the printer at 8x10 size.

Depending on the scanner, it is normally best to use a multiple of the actual scanner CCD density rather than setting the resolution in between, because then the scanner software will have to interpolate, and that is better to do in PS.

If all you need is an 8x10, I would scan at the nearest higher native resolution of the scanner, which is probably 1200 SPI, and then resample it in PS to the final resolution you need once you have done the croppping and other adjustments. Sharpen after the final resizing.

---Michael

[Neal Shields]

That decision should be driven by the printing device that you are using.

Fuji Frontier for example prints at 300 dpi, so you would need to scan a 4x5 at 600 dpi.

Ink jet printers use several dots per pixel to get the colors so you don't need to scan a 4x5 at 2400 to supply a file to a 1200 dpi ink jet.

The long and short of it is, I don't think you will see any improvement on an 8x10 digital print by scaning above 600 dpi.

Depressing isn't it.

That is why, I am transitioning to 8x10 B&W. It is getting very difficult to get a good optical print from my 4x5 negatives, next to impossiable from a 4x5 transparancy.

One of the reasons that you have so much trouble finding the data is no one wants you to know the true resoulation of the digital printing methods.

I finaly found a link to the data on the Fuji printer.

http://home.fujifilm.com/photokina2002/data/ct_pdf/lb_204e.pdf

[Don Wallace]

Michael, thanks for the quick reply, but I guess I need to go back to school because I have no idea what you just said. I have an Epson 4870 and I want to scan a 4x5 reversal to print an 8x10 on my R800 printer. I use Photoshop Elements.

[Bruce Watson]

What Michael said.

Basically, figure out your degree of enlargement (in this case, 2x). Find the output resolution for the printer (Wide Format Epson inkjets 360ppi, Lightjets are usually 304.8 ppi, etc.). Multiply them together. Then, use the next higher native resolution for the scanner.

Alternatively, you could use the scan-once-use-many idea. Scan for the biggest print you ever think you'll make (say, 10x which is roughly a 50 x 40 inch print from 5x4 film). Do all your work on this large file. At print time, you resize to the proper print size, do an output sharpen, and send it to the printer.

[Michael Mutmansky]

Don,

Bruce has it right as far as the formula goes.

For the scanner and printer you have, I would scan at 1200 SPI (samples per inch) and then resize it in Photoshop to be 360 PPI (pixels per inch) at the size you want to output.

I disagree with Neal about there being no point scanning over 600 SPI, because scanning higher is well within the capabilities of the 4870, and it affords you some cropping, etc. and you will still be over the 360 PPI output that you need to send to the R800. If you scan at 600 SPI, you won't have enough resolution to meet the 360 PPI printer output, let alone if you do any cropping.

Here's how you do it (I think Photoshop Elements works exactly the same as regular PS in this respect).

Scan the image at 1200 SPI.

Load it into PSE and do the basic cropping, etc you want.

Then, go to Image: Image Size...

A dialogue box will come up that shows the size of the image in inches and pixels and it will also have a pixel/inch spot.

Uncheck the Resample Image box, and then change the one image size dimension to whatever you want (8", or maybe you wnat 7.5", or whatever) As long as the Constrain Proportions box is checked, it will make an adjustment to the other dimension as you enter the first.

You will notice that it has changed the other image size dimension proportionally, and it also changed the pixels/inch value accordingly.

Then, re-check the Resample Image box, and adjust the pixels/inch value to 360. You could change the sampling method to Bicubic Sharper if yuo want, but you get a bit better control using Unsharp Mask or Smart Sharpen later.

When you hit OK, the image will be resampled to the physical size you want, and you will have the PPI value you need for best results in printing.

Then, I would go to Filter: Sharpen: Unsharp Mask or Smart Sharpen and give it a little tweak. Smart Sharpen works very well most of the time, with a value of about 30% to maybe 50% in my experience.

Then, it's ready to go to the printer.

---Michael

[Oren Grad]

Don, here's a tutorial that starts at a very basic level. Among other things, it explains in detail the relationship between scanning resolution and printing resolution.

[Juergen Sattler]

Dan,

I was completely cluesless about scanning before I attended one of Michael's and Ted Harris' scanning workshops. They really take the time to explain what it takes to make good scans and what manipulations you should do during scanning and which ones are better left for Photoshop. I highly recommend that you attend their next workshop which will be right after the View Camera Conference near Chicago (don't know the exact date or locations, but that's easy to figure out.) Good Luck and have fun!

[Ted Harris]

Jurgen,

Thanks for the kind words. A bit more detail. The half-day abbreviated workshop that is part of the View Camera Conference is now full, as, I believe are all the other Conference workshops except the Wet Plate Workshop which still has a few spots open. The next full 3 day Large Format Scanning Workshop is the weekend before the View Camera Conference. The dates are June 2 - 4 at Midwest Photo's Gallery in Columbus, OH. There is one and possibly two places left in this workshop.

[Brian Ellis]

The advantage to attending in Columbus is that Jim may take you to Dante's Pizza. I'm always skeptical about claims of "the best pizza you've ever eaten" but Dante's really was. And of course the workshop is o.k. too. : - )