Filters > Distort> Equations Noise()

[John Rostron]

WARNING: for the technically-minded only!

The Noise functions in the Filters > Distort> Equations facility are supposed to add (unspecified) noise to an image. The only description I can find of this is in the video by James Ritson. He first duplcates the layer and then uses either noise(x*y)*a or noise4(x*y)*a in his equation. This produces a grain-like effect over his image.

The documentation for equations is limited. There is the Expressions for field input in the Help system which gives, under : Noise(seed/x,y), an explanation:  

Generate 1D noise either from a seed or based on X/Y input

 with similar definitions for noise2, noise3 and noise4.

James uses both the noise and the noise4 functions. In his video he is using the single seed parameter x*y, with the magnitude controlled by the a parameter. 

I have been experimenting with these noise functions and present here my findings

• Although the Expressions for field input names the functions Noise ... Noise4, with a capital letter, these will not work. You need to use a lower case n for noise.
• The function noise2 has no effect.
• The functions noise, noise3 and noise4 seem to produce identical visible results. The histograms are also identical.
• Using a single parameter, either a simple number, or an expression such as x*y, has no visible effect unless the Full option is selected in the Extend Mode at the bottom.
• When using two parameters, they need to be different in the x and y axes to produce any visible result.
• Multiplying the parameters by a number, such as noise(10x,10y), has no visible effect.

I show here the effect of varying these parameters on a simple gradient field:

Here is the effect of x=noise(x,y) and y=noise(y,x):

The results for noise3 and noise4 are identical, as are noise(3x,3y) etc as are the histograms.

If the parameters are the same, say x=noise(x,x) and y=noise(y,y) You get a very different effect: 

Almost like a tartan effect.

If the noise functions are the same in both x and y such as x=noise(x,y) and y=noise(x,y), it works OK, but if you use x=noise(y,x) and y=noise(y,x) there is no visible effect unless you select Full:

The difference between using Zero and Full in the Extend Mode at the bottom is subtle. Using Full seems to convert the image into a monochrome effect with the background invisible. However, the noise is based on the luminance of the background.

Just for comparison, I append here the effect of the effect of the Add Noise filter (Filter > Noise > Add Noise...):

You can control the intensity of the noise here, which is more than you can in any of the noise functions I have described.

In conclusion, I would recommend that if you want noise, then use the Filter > Noise > Add Noise... option above until such time as the devs at Serif come up with a more understandable noise function in Equations. Having said that I am not holding my breath on this. Using noise in equations is probably a minority pursuit amongst users and the Add Noise filter is much easier.

John

 

 

 

[Uwe367]

That's very interesting. Thank you.

[Pariah73]

thank you for this post!

[Uwe367]

This is really a very interesting Filter. Is there a listing available where are all possibilities listed?
I think there are much more possibilties than only noise and twirl or not?

[John Rostron]

4 minutes ago, Uwe367 said:

This is really a very interesting Filter. Is there a listing available where are all possibilities listed?
I think there are much more possibilties than only noise and twirl or not?

I take it you are referring to Filters > Distort > Equations. You need to look in the Help system for ''Field Expressions'. It includes all the standard arithmetic, algebraic  and trigonometric expressions. You can use these in any context where you might input a number, such as Document > Resize, where you could put 50% or *0.5 or even sqrt(w). (w is the width.)

John

[Alfred]

8 minutes ago, John Rostron said:

You need to look in the Help system for ''Field Expressions'.

Expressions for field input

The online Help has yet to be corrected. It currently says

/2	Divide by a half.

when it should explain ‘/2’ as either ‘Divide by two’ or, less obviously, ‘Multiply by a half’.

[Uwe367]

1 minute ago, John Rostron said:

I take it you are referring to Filters > Distort > Equations. You need to look in the Help system for ''Field Expressions'. It includes all the standard arithmetic, algebraic  and trigonometric expressions. You can use these in any context where you might input a number, such as Document > Resize, where you could put 50% or *0.5 or even sqrt(w). (w is the width.)

John

Thanks John and Alfred.
Yes, i mean this Filter.

[dmstraker]

Helpful. Thanks John. Nice presentation of findings, too.

Further playing:

• Polar, r blank, t=noise(a,b) gives circles using image colours
  • Could be good as a background frame for actual image (use non-zero Extend Mode)
• Polar, r blank, t=noise(r,r) gives interesting dotty spacey circly thing (umm)
• Cartesian, x=a*max(x,y), y=b*min(x,y) gives diagonal flip.

Oh dear. I see hours of pointless fun ahead...

[John Rostron]

16 hours ago, dmstraker said:

Oh dear. I see hours of pointless fun ahead

Don't tempt me!

John