Removing Color Noise Without a Third-Party Utility: i.e. Noise Ninja, Neat Image

[cyclohexane]

*in this thead I've used "grain" in the place of "luminance noise" and "color noise" in the place of "chroma noise"*

For those of you who don't read the sports forum, here's an edited version of the noise reduction technique I posted.

Here, we have an image (not brilliant, but it works for the demo):



This is an image from my D2H; there's actually a funny story behind it, but I'll save it for later. Expsoure data is 1/125 second, f/2.8, ISO 1600. Underexposed 1 stop. Here, I've already bumped it up one stop (virtual 3200, I guess) in ACR, but have not used ACR's sharpening, luminance smoothing, or color noise reduction tools. Admitedly, it looks fine at web size. Below is a crop from the full-size image:



We're being attacked at color noise here, and it doesn't look pretty. This is well into "It'll show up even when printing" range. So, how do we get rid of it? Personally, I don't really like ACR's color noise reduction tool, as I feel I can do a better job. The ACR tool is actually pretty decent, but I find myself having to clean up after it anyhow, so I prefer just to do it myself. Here's what I do:

1. Convert the open file to LAB Color.

2. Select the A channel. Select the B channel. Observe. This is where the color noise resides.

3. Apply a light gaussian blur to both the A and B channels. The size is image-specific, but with my D2H I can get away with a radius of 3 to 8 pixels, depending on how much color noise there is, and how much saturation I'm willing to trade for the removal. Of course, if you get color smearing, you should use a smaller radius.

Here's the same image, two gaussian blurs later:



...and a full-size:



This took care of the color noise. While there's still a good amount of grain, I'm personally not bothered by it- and I bet it'll make a decent print. With the luminance smoothing tool, I can remove the grain, but as soon as I apply unsharp mask to the L channel, it'll come right back; might as well keep whatever detail is already there.

[jfrancho]

I too think that NR in ACR is somewhat a blunt instrument, but have found that setting smoothing to 10 and color NR to 3 can get rid of a bunch of noise without adding the "fuzz" that more aggressive settings will. Lab colorspace is really amazing stuff. Once you understand what is in each channel and realize that luminance data is seperated from the color data, all the filters in Photoshop take on a whole new value and purpose. Thanks for posting this, Michael.

[Paul Shields]

Good tips Michael. I particularly like that you've held the detail. I've found the 3rd party noise filters can get very smeary if not used carefully. I've read about this LAB technique in the past but never applied it. I should read up on it a bit more, what with having the world's noisiest DSLR in my posession .

[Blinky]

Cool! I rarely use noise reduction in ACR and don't really know how to get consistent results with it. I've used a vaguley similar technique with the RGB channels but never with LAB. I'm gonna go back and re-process some losers with this.

Thanks!

[Mr. Pickles]

Originally Posted by B

I'm gonna go back and re-process some losers with this.

Doesn't include me does it?

And that is a good tip, so Karma to you for the post.

[Blinky]

Originally Posted by Mr. Pickles

Doesn't include me does it?

Nah, even LAB mode won't help you! :

[Mr. Pickles]

You sure? I'm a Gemini. A and B channel? And I got a little Lightness channel too.

Maybe my internal histogram leans too far to the right?

[macmaam]

Thanks for posting this great tip. Now, where am i going to find an imperfect image to practice on

[jfrancho]

Originally Posted by macmaam

Thanks for posting this great tip. Now, where am i going to find an imperfect image to practice on

I think I have a 500 GB drive full of junk -- where should I send it?

[cyclohexane]

Glad you guys found this useful.

Originally Posted by macmaam

Now, where am i going to find an imperfect image to practice on

If that 500 GB drive doesn't pan out, shoot basketball or volleyball in a gym, and underexpose. Bring up some images, and enjoy.

[dc2]

ER
You mean the 5D or the Oly?

[cyclohexane]

I'm sure he means his Oly E-1, though admitedly I think my D2H gives it a run for it's money.

[Rense]

There* is a whole book about things you can do with the LAB colorspace.

Read it and you'll be surprised!

[Paul Shields]

Originally Posted by cyclohexane

I'm sure he means his Oly E-1, though admitedly I think my D2H gives it a run for it's money.

Yes I do. However, my current motto is 'How I learned to stop worrying and love the noise'.

[cyclohexane]

Thanks for the link Rense. Here's a karma for that.

Paul: Heheheh, great motto. I decided that since we're still outperforming color negative film, it's all good.

[cyclohexane]

I edited the first post in this thread to remove the stinking asteriks that appeared after every sentence which were, apparently, the result of moving the forum to vBulletin. Hopefully, it's a little easier to read now. =)