17 filters for reducing noise and sharpening

[mrme]

Here is an article I wrote about 17 different filters that can be used to sharpen and remove noise. I have found a filter called sharpening with synthesis that seems to sharpen images an a very interesting way. Has anyone else used this filter? If there are any free filters that you like to use that I've missed let me know. I'm always interested in trying out new filters.

I've created a poll for you to vote for your sharpening filters. I'm interested in seeing what's most popular.

[Colin Southern]

I just avoid noise noise in the first place be exposing and composing correctly ... saves a whole lot of mucking around afterwards

[drjuice]

Where is the filter called sharpening with synthesis to be found? I've looked at all my image handling software and don't find it in any of them. Thanks, in advance.

v

[mrme]

The sharpening with synthesis filter is very difficult to set up.
To set it up you have to
1. Install python 2.6
2. Install or re-install GIMP with python support
3. Install the resynthesis plugin
4. Get the sharpen with synthesis plugin from github

Many advanced GIMP users already have the resynthesizer plugin, so it is only one more step for them to install the plugin.

@Colin
I wish I could avoid noise, but I will sometimes get noise when I'm using a ISO as low as 100. So yeah, I'm pretty much forced to having to deal with noisy images.

[Photon Hacker]

The sharpening with synthesis filter is very difficult to set up.
To set it up you have to
1. Install python 2.6
2. Install or re-install GIMP with python support
3. Install the resynthesis plugin
4. Get the sharpen with synthesis plugin from github

Hehe, you should be kidding about the "very difficult" qualification. How would you use to describe the difficulty of writing and debugging -say, this very program- the GIMP? .

P.S: Thanks for the article and for using free software! .

@Colin
I wish I could avoid noise, but I will sometimes get noise when I'm using a ISO as low as 100. So yeah, I'm pretty much forced to having to deal with noisy images.

We could help you with that if you provide more details. Search for dark frame subtraction for a relevant method to reduce the noise associated with long exposures if that's the case.

[mrme]

Hehe, you should be kidding about the "very difficult" qualification. How would you use to describe the difficulty of writing and debugging -say, this very program- the GIMP? .

Yeah No kidding. I'm glad there are so many people willing to put in time to continually improve GIMP. I wish them all the best of luck. Have you tried to build GIMP before?

I've heard of dark frame subtraction before, but I've never tried it. I'll doubt it'll help that much, but it's still worth a try. I'll report back the results of me using dark frame subtraction once I try it out.

The reason I have such a big problem with noise, is because I use a cheap $350 non-SLR camera. Yeah...

[Colin Southern]

I wish I could avoid noise, but I will sometimes get noise when I'm using a ISO as low as 100. So yeah, I'm pretty much forced to having to deal with noisy images.

Hmmm - that begs the question "why are you getting noisy images?" - ususally the culprit is under-exposure. Do you have a RAW file you can send me to illustrate the problem?

[mrme]

Hmmm - that begs the question "why are you getting noisy images?" - ususally the culprit is under-exposure. Do you have a RAW file you can send me to illustrate the problem?

Here's a picture I took of my Dad on his Birthday. The ISO is at 200, and there is a ton of noise.
Original picture:

crop:

The Raw file can be found at
https://docs.google.com/open?id=0B0_...FhQZGxfWk5GTHM

[thatguyfromvienna]

Colin appears to be right regarding underexposure.
The windows and blinds are bright, thus making the faces way too dark to avoid the bright spots from blowing out.
A fill flash would have helped a long way, I guess.

But then again, you mentioned earlier that you're using a P&S camera with a small sensor.
In that case you're in bad luck unfortunately since many P&S still these days become very noisy from ISO 200 on.

[Colin Southern]

Here's a quick copy/paste from another post I wrote on noise / dynamic range / ISO that might serve as a good primer here ...

When you think about it, the light "gathering" characteristics of the camera's sensor are set in silicon - so all of the magic of high ISO can only happen electronically. So if you're shooting at - say - ISO 800, all that's really happening is you're (as far as the sensor is concerned) (need to word this carefully!) only feeding it 1/8th the amount of light that it would have got at ISO 100 if the light was 8 times stronger. So to put that another way, if you have a 12 foot well with fresh water at the top - mud at the bottom - shooting at ISO 800 is like taking water 3 feet down from the top - which is also 3 feet closer to the mud. But if that pipe was ALREADY 2 feet in the water (meaning a 2 stop under-exposure) and you lowered it an additional 3 feet then the water isn't as clean and as clear as it would have been 2 feet further up. In a digital context this means you're getting closer and closer to the noise floor.

In a camera sense, it's not the under-exposure that causes the noise per se (if you want to test it, set your camera to it;s highest ISO setting - under-expose a shot by 10 stops - and you still won't see any noise - BUT - it's when you try to adjust that under-exposure out in post processing you find that the signal & the noise floor are basically one and the same, and you can't display one without revealing the other ... so the "trick" is to stay as far away from the noise floor as possible - and that means not under-exposing. Even over-exposed looking on the review screen in fine so long as important areas aren't blown. It's one of the few occasions where ETTR (Expose to the Right) is actually beneficial.

Basically the problem above - it it's shot with a point & shoot is that it's shot with a point & shoot! They CAN take a nice photo, but because of their small sensor sizes - and lots of pixels - their dynamic range is "bottom of the barrel". If you have a purely reflective scene (bride in white dress standing in the sun next to a groom in a dark suit who is also in the sun) you only need a 4 stop dynamic range - and they'll cover it easily. But when you shoot someone silhouetted against a window - expose for the window - and try to show foreground detail (that's in shadow) then the dynamic range of the scene increases dramatically - and p&s cameras just can't come close to coping.

There are 4 choices that I can think of ...

1. Use noise reduction software. Unfortunately, this is probably the worst option ... trying to repair low-quality data is ALWAYS going to be a compromise. Far easier to just get higher quality data in the first place. So how does one do that? ...

2. Use a fill-flash to reduce the dynamic range requirement (ie "balance the scene)

3. Use a reflector to accomplish the same thing ("poor man's fill flash") (but amazingly effective)

4. Use a camera with a far greater dynamic range capability (eg SLR) (but even they can struggle with shots like this).

Hope this helps.