Sharpening a noisy, high-ISO image

[futureal33]

Afternoon all,

Something I have been wondering for a while, and I may soon have a situation where I will need to do this, so thought I might as well ask.

I like nice sharp images, as do most of us, and I also like nice shallow DOF images, which means shooting a lens often wide open. That means I must apply more sharpening than if I was shooting at f8 (in general).

If I am shooting at around ISO 6400 on a 5Dmk2, the images generally look OK, with a bit of noise at pixel level, but at full size viewed on my monitor, you CAN see the noise, but not massively so. However, I still feel like the image needs sharpening. As soon as I try to apply any kind of sharpen, that "not so bad" noise, becomes very grainy obtrusive noise - which is now visible at full size view.

So, my question, is how do you sharpen an already quite noisy image, without increasing the noise too much?

Im definitely in the camp of preferring a bit of noise to a "smoothed out" photo, so I tend not to use NR software, other than maybe a bit of it applied during import through ACR (generally no more than 25pts luminance @ detail 50%), so Im hoping not to have to resort to getting plasticy smooth images here!

Thanks
Nick

 

[Denyerec]

Your problem (Guessing without seeing the pic) is likely that your noise is smaller than your key details, and you're trying to sharpen at too fine a radius. If the image has regular high frequency noise throughout you could separate that out & try a standard unsharp on the underlying lower frequency image data, but without seeing the image in question I'm just farting in the wind

 

[futureal33]

Ok, this isnt the image, but its a fairly good example.
First is large size, then next is a much larger size, showing the level of noise


Sheepskin Seller Manchester Christmas Market by futureal33, on Flickr

Link to Full size image

http://farm8.staticflickr.com/7007/6553301057_6eba4e8423_o.jpg
Sheepskin Seller Manchester Christmas Market by futureal33, on Flickr

Staff Edit : Sorry Nick. Had to break the large version to a link, but people can still click through to view it. If it helps, you can post a 100% crop of a section of the image to illustrate the issue

 

[PsiFox]

Just tried the large image in Lightroom which did a pretty good job of removing the noise.

You can download a trial.

 

[Denyerec]

Might be in with a shot separating by frequency, got an original-res version online anywhere?

 

[Denyerec]

Ignore the above... got it

 

[Denyerec]

Yeah, even working with the above it was possible to strip the noise off and sharpen the underlying image and that's after whatever you've done to it.
Split @ 0.9 - 1 pixel & work on the lower frequency information, any method will do, I apply the original image into a 1px gaussian blurred copy in subtract mode, with a 128 offset(Scale 2). That'll strip the noise onto the top layer allowing you to work underneath it.

 

[futureal33]

Denyer,
How do I split the frequencies of the image, never done that before!

Thanks

 

[arad85]

If you're using ACR, try applying masking. That's a frequency separation of sorts and if you have lightroom, if you hold the alt key down the mask is revealed to see what you are sharpening and what you aren't.

 

[futureal33]

Andy,
What sort of level masking should I be applying? I have never touched the masking slider before..

Thanks

 

[arad85]

Tr it and see... It is image dependant, but if you hold the alt key down as you slide the slider, the mask is shown. The white bits get sharpening applied, the black bits don't. Have a look here: http://www.image-space.com/Lightroo...l_Sharpening_Mask/Visual_Sharpening_Mask.html (first webpage I hit with google) and see what you need to know

 

[Denyerec]

Apply the original image into a 1px gaussian blurred copy in subtract mode, with a 128 offset(Scale 2). That'll strip the noise onto the top layer allowing you to work underneath it.

Duplicate the background into a layer, then gaussian blur @ 1px. Then use the "Apply Image" command to apply the original Background layer to the blurred layer as above.

 

[Porsupah]

You might also give Neat Image a shot - in trial mode, it's very reasonably limited to non-commercial use, and will only export as JPEG, with EXIF stripped out. Once you've selected a region of the image to build the image's noise profile from, you can then apply different levels of noise reduction per channel (Y/Cr/Cb) and frequency (low, medium, high), with optional sharpening of its own, which tends to be rather smarter than Aperture 3's.

I've had good results with it managing to remove high ISO noise, whilst still retaining fur detail - quite a challenge for such software, given their general fondness for smoothing out such fine detail.