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Question to "High pass sucks" technique

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  #1  
Old 07-10-2010, 11:24 AM
santoro80 santoro80 is offline
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Question to "High pass sucks" technique

I'm just trying this technique (http://www.modelmayhem.com/po.php?thread_id=439098) and I have two questions to the step 2:

"2. Working on the bottom copy, run the gaussian blur filter at the intended pixel frequency (same as you would input into the HP filter)."

1) How do I know what pixel frequency (or radius?) should I choose? I have a 10 Mpx camera.
2) What do they mean by "high pass sucks" or "high pass filter"? This quick de-grunge technique? http://retouchpro.com/tutorials/?m=show&id=213
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Old 07-10-2010, 02:04 PM
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mistermonday mistermonday is offline
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Re: Question to "High pass sucks" technique

Santoro80,

Quote:
1) How do I know what pixel frequency (or radius?) should I choose? I have a 10 Mpx camera.
The radius you chooses has nothing to do with the size of your camera output but the content of each image and each image will be different. There are two ways to select the radius. One would be to perform a Gaussian Blur, adjusting the radius slider until all of the detail / fine edges that you want to protect or heal becomes blurred away. The other way is to perform a High Pass Filter adjusting the radius until the detail you want to preserve / heal is revealed. but then click cancel after you determine the radius. The 1st GB method is usually easier to accomplish visually.

Quote:
2) What do they mean by "high pass sucks" or "high pass filter"? This quick de-grunge technique? http://retouchpro.com/tutorials/?m=show&id=213
The Filter>Other>High Pass has been in PS for 20 years. It was never intended to be precise and because of the math algorithms and other reasons, it is not accurate. So when you create a split frequency set of layers using the conventional HP Filter, you loose quality, visually noticeable particularly in the highlights and shadows.
The method used in that ModelMayhem thread is an alternate way of creating a High Pass layer which is very precise. So if you were just interested in creating only an accurate HP layer, you could create the split layer set and just delete the GB layer. If you compare both methods on a image that has a wide tonal range you will be able to see the difference.

As for the DeGrunge technique, no it is not the same. However the two have some things in common. When you split a layer into spacial frequencies what you effectively have is a formula that says: GB+HP = Original. This will be true at any radius and indeed if you toggle on and off the background layer below the split layers you will see they are visually identical.
For the DeGrunge technique you are actually creating a third component and the following formula: GB + HP + Degrunge = Original. In this case you create a layer where you are protecting all of the fine edges smaller than some radius 1 (HP) and blurring all edges greater than radius 2 (GB) and everything in between represents the grunge. The point to take away from this is that when making a Degrunge layer, you can use the Frequency Split technique to create the HP layer that you would use in the DeGrunge technique. You just make the split then delete the GB layer. Its a few extra steps which you may or may not find worth the extra effort.
Regards, Murray
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Old 07-14-2010, 04:08 PM
santoro80 santoro80 is offline
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Re: Question to "High pass sucks" technique

Thanks for explanation. It was very helpful!

I just want to use this technique for skin retouching.
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Old 07-14-2010, 04:17 PM
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mistermonday mistermonday is offline
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Re: Question to "High pass sucks" technique

It works well if you choose the radii carefully and try not do overdo it. If used properly it will save you considerable time instaed of dodging and burning and will not look blurred.
Regards, Murray
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Old 07-15-2010, 08:26 AM
KTG KTG is offline
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Re: Question to "High pass sucks" technique

I have been experimenting using Inverted High Pass with Apply image. One workflow I am using is making three layers: One with the radius at 3, one with 6 or 9 and one with 18 and selectively applying them to areas of the skin. I read where Natalia uses much larger radii, but I cannot get any effect at a very high radius. Murray is right. If done properly one can reduce greatly the amount of d&b. Which I do after the high pass technique. Any thoughts?

k
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Old 07-15-2010, 08:57 AM
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Godmother Godmother is offline
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Re: Question to "High pass sucks" technique

Quote:
Originally Posted by KTG View Post
I have been experimenting using Inverted High Pass with Apply image. One workflow I am using is making three layers: One with the radius at 3, one with 6 or 9 and one with 18 and selectively applying them to areas of the skin. I read where Natalia uses much larger radii, but I cannot get any effect at a very high radius. Murray is right. If done properly one can reduce greatly the amount of d&b. Which I do after the high pass technique. Any thoughts?

k
Always depends on the quality of the original image. If you're working on a 2000 px wide image a larger than 30 won't work. Most of my image are 8000px wide tho so you can understand :P
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Old 07-15-2010, 09:02 AM
KTG KTG is offline
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Re: Question to "High pass sucks" technique

Ahhhhh, yes. Thank you GM.

k
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Old 09-25-2010, 10:54 AM
Setcamper Setcamper is offline
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Re: Question to "High pass sucks" technique

Trying to wrap my head around what the ModelMayhem thread is actually doing. After completing the 8-bit steps I'm left with 3 layers; my base background image, a layer that's blurred significantly and then a highpass-like layer created using the apply image steps. When all three are turned on I have my original image. What am I supposed to edit or mask to even tones but keep the detail.

I understand how the de-grunge tutorial works because I'm left with a single layer on top of my original that both even tones and holds detail in the areas I un-mask.
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Old 09-25-2010, 12:05 PM
ShadowLight ShadowLight is offline
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Re: Question to "High pass sucks" technique

depends where you have split the frequencies... but in short you can:

1) pain on the blurred layer to relax shadows/correct colours
2) use heal-brush with settings (current layer only) on the "highpass" layer
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Old 09-25-2010, 12:06 PM
jonjon925 jonjon925 is offline
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Re: Question to "High pass sucks" technique

The blurred layer is the one with the low frequencies of the image and there you can play with the smudge tool to even out things.
The highpass-like layer is the one with the high frequencies of the image and contains texture (facial hair, pores, pimples, hair texture etc) and this is where you use the stamp tool or the healing brush.
These layers are not supposed to be masked out or something like that. You choose the layer you want and you edit it.
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