Noise and Anti-Aliasing Issue

[sanking]

I have been scanning a lot of medium format color negative film recently and have apparently met the nasty creature called anti-aliasing. And, just as some experts suggests, it is more of a problem with my sharper scanner that focuses better and gives more resolution (an old Leafscan 45) than with the softer Epson 4990.

After some research I found a program called Neat Image that according to some experts does a good job of minimizing noise and the grainy look from anti aliasing. Question is, does anyone have actual experience with this, or other products that offer the same solution?

Sandy King

[dwross]

What's anti-aliasing (besides noise and grain)?

[sanking]

What's anti-aliasing (besides noise and grain)?

It is a kind of interference pattern between pixels and grain that accentuates grain with some films, mainly high speed color films, at some resolutions. It appears to be primarily a hardware issue, though some post-scanning software may minimize its effects.

You may not see it unless your scanner is capable of effective scans in resolution of 53 lppm or more.

Sandy King

[Donald Miller]

Sandy, I don't have experience with your particular program. I recently purchased and downloaded Noise Ninja and am very impressed with what it accomplishes.

There have been some complaints on the NN forum about the latest upgrade being late in coming...but I have no complaints with what this program provides. However, it should be noted, that my experience lies in digital print output and not with enlarged negs.

[ike]

Aliasing is a sampling phenomena. The Nyquist sampling theory says that you must sample 2x the highest frequency in the actual data. The so called Nyquist frequency. Typically you would filter the data content at the Nyquist frequency before sampling otherwise any data above Nyquist will appear to mirror itself back upon the lower frequencies and distort the data. This filter is called an Anti-Aliasing filter. In optical systems where the data is two dimensional cameras and scanners typically have an optical low pass filter. What I would suspect you are seeing is actually gain aliasing, not anti-aliasing.
So how does all this mumbo jumbo help? Probably not much, you might try scanning at lower resolutions and then up sample the image manually. This based on the hypothesis that the scanner doesn’t really have it’s published resolution.
Ike

[jd callow]

Its grain aliasing if i understand the post correctly. It seemed to be an issue with the flextight II and the Eversmart pro when scanned at or near max resolutions. I found no perfect cure. One thing that makes it less prominent is to make sure that there is no USM being applied during the scan. I believe that Imacon started using a diffused light source in later models in an effort to reduce grain aliasing. The Eversmart had a wet mount system that I'm told improved all aspects of transmissive scans, but never used it.

[Baxter Bradford]

I have been using Neat Image for some while to remove this unfortunate characteristic of scanning colour neg films. Whatever the origins, C41 film looks awful in the 'grain' department fresh off the scanner compared to E6 and B+W negs.

It has been a major success - I can now use C41 film to obtain images which E6 wouldn't have handled.

I only use in 'Auto' setting since it seems to do all I want without having to tweak sliders; possibly cleaning image up too much in some instances. However not been motivated to try to expend energy learning yet more software intricacies.

To ease use, I have stored presets for film type, format and resolution. The latter being important as magnifies film grain/noise.

[sanking]

I have been using Neat Image for some while to remove this unfortunate characteristic of scanning colour neg films. Whatever the origins, C41 film looks awful in the 'grain' department fresh off the scanner compared to E6 and B+W negs.

It has been a major success - I can now use C41 film to obtain images which E6 wouldn't have handled.

I only use in 'Auto' setting since it seems to do all I want without having to tweak sliders; possibly cleaning image up too much in some instances. However not been motivated to try to expend energy learning yet more software intricacies.

To ease use, I have stored presets for film type, format and resolution. The latter being important as magnifies film grain/noise.

Is this Neat Image used during the scan or in post-processing after the scan?

Sandy King

[Baxter Bradford]

Neat Image used as post-processing after the scan is safely on the hard-drive. Then apply customised capture-sharpening using Photokit plug-in.

Wasn't aware you could use Neat Image during the scan. As I said, I try to keep things as simple as possible.