Stacking for noise

[arith]

Just some information, over the weekend I tried the stacking method for noise reduction but not to remove noise, to clear streets of people and traffic.

It worked; I took 20 exposures with an intervalometer, but I don't think I need more than 8, it was too hard to stack them in PSE so I used Helicon Filter.

I say it is for information only since I pushed the lens past infinity and they are all out of focus. But you can see it worked.

The method is to use 100% alpha on the base layer, 50% on the next, 25% and so on down to 1%. Of course if there is too many people or traffic it won't work.

[chauncey]

It is said that the new versions of LR do a superior job of NR over PS CC...would be interesting to run
a series of images thru LR using less than normal NR and then blending/merging them in PS.

[arith]

Thanks Chauncey, I'm surprised that all the buses and people completely disappeared, but I did it at 0530 in order to avoid mass crowds and party revellers. Shame about the focus but I dare not stay too long with a device with flashing lights on it. I forgot that this lens went past infinity.

[arith]

One of the images, a bus, where it go. I think this is a useful technique for architecture photography, unless you really like traffic and cost a lot pedestrians.

[DanK]

Would a median blend of a stack accomplish the same thing?

[arith]

I do not see why not Dank, I haven't got the software but any noise reduction using stacking might work. I think things will get interesting where places are so crowded that the background is obscured for too long, maybe that bit turns into a smoke of colour.

http://petapixel.com/2013/05/29/a-lo...dian-blending/

[proseak]

Here's a median stack taken in the rush hour in Cambridge

[DanK]

Here's a median stack taken in the rush hour in Cambridge

Peter,

Thanks for posting this

Dan

[Cantab]

Here's a median stack taken in the rush hour in Cambridge

Peter, a very interesting shot. How many images did you have in the stack?

The only possible difficulty with the photo is that it looks unnaturally empty of people! Which college is this? I spent a year Cambridge many moons ago but don't recognize it.

[arith]

That is so impressive, I cannot believe it is the rush hour. Not a hint of people or cars.

[proseak]

It's Christ's College, taken at 6.30pm 28 March, handheld. I set to Jpeg, continuous, and kept going until it stopped - 20 in all. Then select all in Bridge, load as Photoshop layers, align, convert to Smart Object. Change Stack Mode to Median.

[Ken MT]

Could you also upload a single shot to show what it really looked like.

[proseak]

This is a downsize of one of the images - curves, converging vertivals etc not done yet

[arith]

Although it's impressive, I can't get my head round how it works. But I am impressed and wished I had such sophisticated software.

[DanK]

Although it's impressive, I can't get my head round how it works. But I am impressed and wished I had such sophisticated software.

Both how to do it and what it does are explained here, although the explanation is not very detailed. The bottom line is that it looks for the typical value for each pixel location. If in a few shots, some pixels are dark or very bright because a car drove by, it will ignore those values. Since it is the median, rather than the mean, the value chosen will simply be in the middle of the distribution. It's otherwise unaffected by darker and lighter pixels in the same location.

[proseak]

Steve, you can achieve the effect with what you have. Once you've imported as layers, either use layer masks to paint out the people who move in each layer until all that's left is the stuff that doesn't move, or use the erase brush on each layer.

HTH

Peter

[arith]

Cheers Peter