I am having 35mm negatives scanned (18 mB) and when I print them at 300 ppi I get grainy images. I see the "grains" also in photoshop at 66% size. What can be the reason ? I can eliminate the grain using the blur filter but this affects the sharpness (of course).

By the way I noticed also the same when I had some scans made for 120 size negatives in professional Kodak Photo CD (45 mB).

Thanks for your help.

tomas

-- Tomas Lang (tlang@uci.edu), July 06, 2000

Answers

The problem is most likely aliasing between the film grain, and the regular pixel "screen" during digitisation. I've noticed the problem myself with negatives. It usually only shows up on 200 ISO or faster film. The faster the film the worse the effect, even though the actual film grain doesn't get much more obtrusive, the alising does. I've tried to illustrate what happens with a simulation. (first time I've tried posting images, I hope this works. Fingers crossed.

The left image is random noise to simulate the film grain, the middle image is a regular pixel screen, and on the right is what happens when the pixel screen is mixed with the grain. (If you want to try it for yourself, use "apply image" in Photoshop, and difference the grain and the pixels). If you have no control over the scanning yourself, the only answer is to use slower film.

-- Pete Andrews (p.l.andrews@bham.ac.uk), July 07, 2000.

Viewing images at 66.67% in Photoshop will never give you accurate results. Not that thats the entire problem but its only showing you a "simulated view". Vew at 100% and see if you have the same problems. At 100% you are viewing pixel for pixel and can make accurate judgements. All filters such as unsharp mask should always be performaed at 100% magnification or else your not really seeing the final effect correctly.

-- Cris Daniels (danfla@gte.net), July 07, 2000.

Unsharp masking if improperly done will make a grainy image. The other source can be the printer itself. What type of printer and what settings are you using? Use the finest print settings you have along with the highest quality. There should be minimal grain visible at 300 dpi and 8X10 and certainly none from the pro photoCD. Any pixillation caused by the monitor will not translate to the printer either. Make

-- jonathan ratzlaff (jonathanr@clrtech.com), July 08, 2000.

Just to clarify matters. My simulation has nothing to do with the monitor. I was attempting to show what happens in the scanner when the film grain size approaches the resolution of the scanner itself. Once the film grain has aliased with the pixelisation process, it's all over. There's no filter that can recover the situation.

-- Pete Andrews (p.l.andrews@bham.ac.uk), July 10, 2000.

The one question I haven't heard mentioned is, "what is your scanner's optical rating and what did you scan the image at?" An 18 MB file sounds fairly low-res, so I'm guessing it's no more than 300 DPI, and slide film has more detail than that.

The other question that begs to be asked is, "what's the highest your printer can handle on DPI?" If you're printing under its capabilities, I'd suggest a higher scan rate.

There's also the question of what kind of slide film you used, for example, Kodak TMax 400 (I know, it's not slide film) is inherently grainy and only gets worse the more you enlarge it. Or, for argument's sake, it could be a bum batch of slide film that hit the market.

-- Sue Bald (destiny3@ix.netcom.com), July 14, 2000.