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Extended frequency separation

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  #1  
Old 12-30-2010, 09:42 AM
fraiseap fraiseap is offline
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Extended frequency separation

I have been playing around with frequency separation using a couple of methods;

1. Using surface blur to create a low frequency layer and using high pass to create a high frequncy layer and blending the two with linear light

2. Using the Model Mayhem technique of creating a low frequency layer using Gaussian blur and using "apply image" to subtract this from the original to create a high frequency layer.

My concern is that 1. uses high pass which is not exactly the mathematical equivalent of <original minus low frequency> so I am losing data. In contrast 2 does not get rid of the grunge.

So that got me wondering if I should modify the Model mayhem technique to create a low, middle and high frequency layer which when combined is an accurate representation of the original. I can then tidy up the middle frequency layer using clone tool, healing brush and D&B. I can also reduce the opacity of the middle layer if required.

Has anyone tried this? Is it the same as the quick degrunge or not? Is it worth the effort?


I should add that I know D&B is superior but, as a working portrait photographer I cannot spend hours on an image so I need something quicker but effective.
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Old 12-30-2010, 10:06 AM
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Der_W Der_W is offline
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Re: Extended frequency separation

You can use Surface Blur for the low pass and the apply image to create the according high pass, that won't change anything with the accuracy :-).
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Old 12-30-2010, 10:14 AM
Flashtones Flashtones is offline
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Re: Extended frequency separation

You can use Apply Image on the Surface Blur same as if you used GB

If you want to split the image on multiple frequencies Sean has made a PS script that allows you to split the HF data across as many layers as you want. For instance, if your Blur radius is 10 px, you can ask for that to be split among as many HF layers as you like, so if you choose 5 layers each would span 2 px of HF data.

That's probably not clear, but check the links on the opening post of the HPS thread and you should see links to the action and Sean's description.
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Old 12-30-2010, 10:20 AM
fraiseap fraiseap is offline
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Re: Extended frequency separation

Thanks for that. It is good to know that surface blur can be used as I prefer that (it avoids bleed from lips, dark hair etc).

I think the actions to split the high frequency layer is exactly what I need. Where do I find the post you referred to?
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Old 12-30-2010, 11:04 AM
Flashtones Flashtones is offline
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Re: Extended frequency separation

Quote:
Originally Posted by fraiseap View Post
I think the actions to split the high frequency layer is exactly what I need. Where do I find the post you referred to?
The model mayhem high pass sucks thread, which I don't currently have a link for. Just google it. the opening post contains many links worth exploring.
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Old 12-30-2010, 11:11 AM
fraiseap fraiseap is offline
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Re: Extended frequency separation

Thanks,

for those reading this, here is the link

http://www.modelmayhem.com/po.php?thread_id=439098
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Old 12-30-2010, 11:24 AM
Flashtones Flashtones is offline
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Re: Extended frequency separation

Scanning that first post briefly, I don't see a link to Sean's script. Hopefully someone can direct you, but really, you should take the time and read the whole thing through. It's time well spent.
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Old 12-31-2010, 06:29 AM
fraiseap fraiseap is offline
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Re: Extended frequency separation

OK, I have now read most of the MM thread and it is very informative (especially if you ignore the "you are destroying art" type rants). I have also found Sean's blog which is extremely good

http://sean-blog.twicebakedphoto.com...equencies.html

Now I have a thought. You could create 3 layers - a low frequency layer by applying blur (Guassian, median or surface) a high frequency layer (either by using high pass or subtracting the blur layer from the original as described by Sean) and a middle layer by applying a bandpass filter between the frequencies of the other two layers. This would allow me to do what I wanted (edit the middle -or grunge- layer without affecting texture or shape)

I tried this and the combined image looked OK but had too much contrast. So my question is, should I reduce contrast of the top two layers to 50% and use linear light for both? Or have I missed something?
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Old 12-31-2010, 06:42 AM
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Cron Cron is offline
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Re: Extended frequency separation

You need to make the layers in order low -> middle -> high. The second blur should be made to the (to be-)middle frequency layer.

You'll need a "help-layer" of Low+Mid after the second blur to make the high freq layer.

1. Copy background 2 times, name them from bottom to top: Low, Mid, High
2. Blur Low and apply Mid normally and set to Linear Light
3. Blur Mid and Copy Merged (Low+Mid) the resulting image to a layer and name it Help
4. Apply High using Help (instead of Mid) and set to Linear Light
5. Hide/trash Help

Last edited by Cron; 12-31-2010 at 06:52 AM.
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Old 12-31-2010, 07:08 AM
fraiseap fraiseap is offline
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Re: Extended frequency separation

Brilliant - thanks. All working now.
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