Re: Adding a little noise

On Tue, 2 Dec 2014, Paul Schmidt wrote:

> I am using Magick++
>
> I would like to add some noise to an image, but the addNoise function adds
> far too much noise.
>
> Using convert you can use -attenuate to cut it back, so how do we do this
> with Magick++ which has no -attenuate option.
>
> I'm an old film guy and the addNoise makes it look like you took 35mm Tri-X,
> pushed it about 4 stops then blew it up to about 16x20...
>
>
> I'm more interested in grain that is barely noticeable.
>
> Any one have any ideas?

Yes, you can use the quantumOperator() method.  Specify the desired 
ChannelType argument (e.g. AllChannels) as well as the QuantumOperator 
argument (e.g. NoiseGaussianQuantumOp) with a relatively small rvalue 
such as 0.25 or 0.5 (I think 1.0 is full-range).

The math looks like

   new_value = old_value + rvalue*noise

where noise is a floating point value which flops around greater and 
less than zero.

This can be tested from the GraphicsMagick command line like

   gm convert infile.ppm -operator All Noise-Gaussian '50%' outfile.ppm

Probably we should add more versions of addNoise() and 
addNoiseChannel() which take a parameter for the degree of noise to 
add.

Bob
-- 
Bob Friesenhahn
[email protected], http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

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