How to Replicate Photohsop's Unsharp Mask

[Itto Avital]

I want to replicate Photoshop's Unsharp Mask.
I know the basics.

Yet if someone think we could create exactly the affect it would be great.

Both using Layers and the tools inside Photoshop and Mathematically.

Thanks.

 

[Asher Kelman]

I want to replicate Photoshop's Unsharp Mask.
I know the basics.

Yet if someone think we could create exactly the affect it would be great.

Both using Layers and the tools inside Photoshop and Mathematically.

Itto,

Is there some purpose to your quest or is it just for fun?

Asher

 

[Itto Avital]

Just playing with some effects in Matlab.
I just want to replicate Photoshop's exact formula.

I managed to do it for the high pass.
Yet USM is a bit more tricky.

Thanks...

 

[Doug Kerr]

Hi, Itto,

Just playing with some effects in Matlab.
I just want to replicate Photoshop's exact formula.

I suspect that the Photoshop Unsharp Mask algorithm, is not publicly known.

There are Web sites on which the operation of the algorithm is discussed, with example images, but I have never been able to get any of those stories to completely fit together.

Best regards,

Doug

 

[Itto Avital]

Could you point me to one of those sites?

Thank You.

 

[Doug Kerr]

Hi, Itto,

Could you point me to one of those sites?

This one is very interesting:

http://www.cambridgeincolour.com/tutorials/unsharp-mask.htm

I have looked at their examples (on a pixel-by-pixel basis) and I can't completely get the story to come together.

Here's my article on the concept, which also has a commentary on the article I cite above:

http://www.dougkerr.net/pumpkin/articles/Unsharp_Mask.pdf

Best regards,

Doug

 

[Itto Avital]

OK, I managed to write something and it seems to work well.
If someone knows better to get results like Photoshop, Please let me know.
Here it is:

Input and Parameters (Just Like in Photoshop): A - Original Image, Amout, Radius, Threshold.

B - Blur image A using Gaussian Blur with Radius.
C - abs(A - B)

Mask = 1 Where Pixels of C > Threshold, 0 otherwise.

Output = A + Mask * (Amount * C)

That's it.

I hope it would work for you.
For anything that would make it more Photoshop comparable, let me know.