Grain in the sky????

[ignatiusjk]

I recently scanned a B&W 4x5 neg for a target size of 16x20 at 400 dpi and the sky has so much grain showing. Is it possible I scanned at to high a dpi? Will scanning at 300 make any difference? The 4x6 prints I make look fine but 16x20 show so much grain. What to do.

[ljsegil]

Perhaps it's noise rather than grain, not that it helps you much if that is the case. Photoshop has a couple of noise filters, Noise Ninja is a plug-in for PS that works well but can cause a lot of detail loss, or a fancier technique is to create a duplicate layer, run Noise Ninja or you de-noiser of choice on the duplicate and create a mask from that and erase everything but the sky. I have found this will sometimes help, but it is a kludge and a PITA.
LJS

[Donald Miller]

Perhaps it's noise rather than grain, not that it helps you much if that is the case. Photoshop has a couple of noise filters, Noise Ninja is a plug-in for PS that works well but can cause a lot of detail loss, or a fancier technique is to create a duplicate layer, run Noise Ninja or you de-noiser of choice on the duplicate and create a mask from that and erase everything but the sky. I have found this will sometimes help, but it is a kludge and a PITA.
LJS

If your sky is of even tonality, you can select the sky and run a low gaussien blur on the selection.

[jim kitchen]

You will have this issue occasionally depending on several factors, where lowering your scanner resolution, which is really not stated as DPI, will not help you resolve your issue...

You could reduce the increased noise level if you do not over process your sky too, but if you must, the answer is usually a software solution as "ljsegil" suggested. There are good software solutions that can reduce this effect, and use the software solution as a mask, similar to ljsegil suggests.

jim k

[Bruce Watson]

I recently scanned a B&W 4x5 neg for a target size of 16x20 at 400 dpi and the sky has so much grain showing. Is it possible I scanned at to high a dpi? Will scanning at 300 make any difference? The 4x6 prints I make look fine but 16x20 show so much grain. What to do.

This gets reported fairly often. It seems to be a property of certain scanners / software / operators. For example, I used to scan 5x4 Tri-X on an old Epson 2450 and make prints from these scans at 55 x 44 cm (a bit bigger than 20 x 16 inches). My prints were smooth and grainless. Since then I've acquired a drum scanner and have drum scanned the same film and printed at 125 x 100 cm (just under 50 x 40 inches). The print is nose sharp and what many people think of as grainless.

What to do? You could find a scanner that does a better job with your film. You could optimize your film for scanning (takes some experimentation to find optimum but it usually means cutting back on development somewhat to make a thinner negative, and graininess is directly related to density, so this also decreases graininess). You could send the film out to be drum scanned, but be sure you pick a vendor who has some history drum scanning negatives, particularly B&W negatives, and who wants to do that kind of work. You could "fix it in post" as has already been suggested using either some blur or some type of noise reduction software. You can experiment with different scanner resolutions -- some scanners do better when scanning at maximum scanner resolution and then down-sampling to print size. This supposedly also down-samples the noise which might be helpful.

Basically, keep working at it. "Where there's a will there's a way." I've forgotten the attribution for that quote, sorry.

[Andrew O'Neill]

Which film did you scan in? 400ddpi sounds kind of low... Wouldn't you want to scan it in at a higher rez if your target is 16x20? But what do I know...I'll just stick to the darkroom where life is so much easier.

[mikossant]

http://www.scantips.com/calc.html

[Lenny Eiger]

If you want a 20 inch print at 360 dpi, you multiply the two numbers. 360 x 20 = 7200 total pixels required.

With a 5 inch negative, you will need 7200/5, or 1440 ppi on the scanner to get the quality you need. Of course, that is dependent on a 5 inch negative, and 5 inches of image. If you crop, the numbers change. I would suggest a min of 2000 ppi on the scanner.

Lenny