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Author Topic: Posterization appears when using topaz denoise  (Read 1729 times)

Heterodim

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Posterization appears when using topaz denoise
« on: October 31, 2015, 03:45:46 AM »

I have been using topaz denoise for some time and found today that poterization appears after denoise a picture. It appears in the clear sky and dark montains in the image.
I uploaded the pictures before and after denoise with a small strength (0.03). They are in luminance mode so that you can easily see the banding.

Is this problem always happenning when you denoise a clear sky, or can you recommend me a better denoise software? Thanks.
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Guillermo Luijk

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Learn the reason of banding first
« Reply #1 on: October 31, 2015, 06:06:08 AM »

Is this problem always happenning when you denoise a clear sky, or can you recommend me a better denoise software?

Banding in uniform colour areas with soft gradations (typ. skies) is caused by the absence of noise that usually helps to dither the gradation. Your gradations are the softest possible (I checked 1 RGB value steps in the 8-bit range), so the only thing you can do to make them less visible is add some noise, or in this case not denoise so strongly.

Topaz is doing very well, the problem is just with 8-bit displays in this kind of images. You only have 256 gray tones to play with and our eyes often manage to distinguish the gaps.



Regards!
« Last Edit: October 31, 2015, 07:02:35 AM by Guillermo Luijk »
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BartvanderWolf

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Re: Posterization appears when using topaz denoise
« Reply #2 on: October 31, 2015, 08:15:26 AM »

I have been using topaz denoise for some time and found today that poterization appears after denoise a picture. It appears in the clear sky and dark montains in the image.
I uploaded the pictures before and after denoise with a small strength (0.03). They are in luminance mode so that you can easily see the banding.

Is this problem always happenning when you denoise a clear sky, or can you recommend me a better denoise software?

Hi,

When you're denoising very smooth gradients, then the type of banding you see is unavoidable, unless you allow, in this case, Topaz Denoise to also add a bit of grain. The uniform/monochrome grain is much less noticeable than the sensor noise you remove, and you can regulate the amount so it is not really visible at normal viewing distances.

For printed output, there are applications (e.g. Qimage Ultimate) that can add a bit of dithering to the output which works really well.

Cheers,
Bart
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Mark D Segal

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Re: Posterization appears when using topaz denoise
« Reply #3 on: October 31, 2015, 08:51:23 AM »

I've applied noise mitigation, both global and selective to quite a large number photos with ample sky in Lightroom and haven't encountered this problem. But I am careful about the strength of application bearing in mind that viewing the effect at 100% on display exaggerates what the appearance of residual noise would be on say a 13*19 inch print. As well, I am working only from raw files (APSC 24 MP) in a 16-bit raw workflow. I mention all these factors because I think they can contribute to the ease or difficulty of satisfactory noise management, depending.
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Mark D Segal (formerly MarkDS)
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Paul2660

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Re: Posterization appears when using topaz denoise
« Reply #4 on: October 31, 2015, 12:56:13 PM »

A software tool I often use is "Neatimage", for noise removal.  I have had good results with it. 

Paul C

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Paul Caldwell
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Mark D Segal

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Re: Posterization appears when using topaz denoise
« Reply #5 on: October 31, 2015, 01:07:59 PM »

A software tool I often use is "Neatimage", for noise removal.  I have had good results with it. 

Paul C

I agree - it is very good - as are Noiseware and Noise Ninja
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Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....."

DaveKennard

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Re: Posterization appears when using topaz denoise
« Reply #6 on: December 02, 2017, 08:02:39 AM »

Sorry to dig up this old thread, but I just noticed the same when processing an image today. But I'm using a 10 bit display with '30bit' output checked in PS, and working on a 16 bit image. I'm wondering if Topaz Denoise actually works in 8 bit only.
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BartvanderWolf

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Re: Posterization appears when using topaz denoise
« Reply #7 on: December 02, 2017, 10:53:49 AM »

I'm wondering if Topaz Denoise actually works in 8 bit only.

Hi Dave,

No, it returns results in maximum precision (depending on the source image, and Photoshop not being fully 16-bit).

I just tried it in Photoshop with a 16-bit/channel image (with all noise reduction settings maxed out) and there were adjacent pixels that differed 1 or 2 in a given channel with the info readout set to 16-bit (so actually 15-bit +1).

It could, of course, be that the OP's source image was already compromised to less than 15 or 16-b/ch, but then I still assume that when Topaz Detail starts denoising that the resulting pixels can be '16'-b/ch. Similar with NeatImage, single digit differences.

Which is also why I hardly ever Denoise, or I even add graininess, to avoid posterization. When printing with Qimage, dithering is taken care of automatically.

Cheers,
Bart
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Doug Gray

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Re: Posterization appears when using topaz denoise
« Reply #8 on: December 02, 2017, 11:06:13 AM »

I agree with the others here who noted adding a bit of noise is sometimes necessary to mitigate banding when working with 8 bit images. You can, for images you want to print, reduce further the impact of additional noise by first upsampling the DPI. Noise is often your friend and done right, not visible.
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