High-Pass & Gaussian – Choosing the radius

[byRo]

If you take a look at the threads concerning sharpening / blurring / high-pass filter you will quickly discover two things:
1) The radius is very important;
2) Nobody tells you just how to get it right.

Hope this will help out.
[details]

They say the best way to learn is to teach - had to rewrite this three times because I kept on finding better ways to do it.

Have fun,

byRo

[Ed_L]

Please don't add another tutorial for a few days. Although I'm sure this is explained very well, it's going to take a couple of days to sink in. When it does, I'll be looking for another one from you. These are great! Thank you for putting in the work so we can all understand it better.

Ed

[DannyRaphael]

Ditto, "Thank you for putting in the work so we can all understand it better."

An awesome package of knowledge.

[byRo]

As Danny pointed out to me - the "How to use the Graphics Eq." part could use some (a lot) more detail.
Tonight I'll edit the tutorial, but in the meanwhile.....

The green band-pass layers are all initially turned off with blending set to "Normal".
Starting from the bottom:
- turn the layer on;
- take a look at the information and decide:

1) This is something that will help;
2) This is something that is working against you;
3) Neither one or the other.

In the first case change the blending from Normal to Overlay. If the effect is too much change to Soft Light, or if you want more change to Hard or Linear Light.
In the second case invert the layer <ctrl><I> and proceed as above.
In the third case just turn it off and go to the next above.

Note: the initial "Normal" blending is only to help visualize the content of each band, if you are going to use it change the mode to Overlay etc..
If anything else isn't clear - PLEASE ASK.

byRo

[SWEngineer]

Rô, excellent work here! Sadly (for me), I only have Elements, so I can't play with your action file. (If you can coax Richard Lynch into helping make this compatible with his HPA3 work, I'd be deeply indebted to you both.)

Am I correctly understanding that these are true band pass filters? e.g. the 10 - 20 layer (filter) would be (using the invert / linear light subtraction trick) Highpass(20) - Highpass(10) or equivalently GaussBlur(10) - GaussBlur(20)?

This opens up an entire new dimension for selectively modifying images. In addition to tone & color, its obvious now that one can work with "frequency" with near equal ease. The example you posted and your suggestions for using your graphic equalizer barely scratch the surface of what can be done with this tool / idea. At least from my perspective as an artistically challenged, but mathematically inclined person, this may be the most valuable tutorial I've ever read. Thanks so much for sharing this. You are awesome Rô.

-Mark

[byRo]

Hi there, Mark,

Originally Posted by SWEngineer

Am I correctly understanding that these are true band pass filters? e.g. the 10 - 20 layer (filter) would be (using the invert / linear light subtraction trick) Highpass(20) - Highpass(10) or equivalently GaussBlur(10) - GaussBlur(20)?

Well, as true as PS will get you*. A more practical way to generate the band is to do the high-pass filter at the higher radius limit (e.g. 20) and then G.Blur the layer at the lower limit (e.g. 10)

Originally Posted by SWEngineer

Sadly (for me), I only have Elements, so I can't play with your action file.

The action file is just a quick way of making up a whole load of bands. With a bit of practice you can estimate a good band and do the High-pass / GBlur trick above.

Originally Posted by SWEngineer

This opens up an entire new dimension for selectively modifying images. In addition to tone & color, its obvious now that one can work with "frequency" with near equal ease.

Exactly

Originally Posted by SWEngineer

...but mathematically inclined person...

*Then you're going to just love the FFT (Fast Fourier Transform) stuff!

Rô

[JustChecking]

thanks for an extremely interesting article

reminds me a bit of my first lectures in image processing, when i've been trying to figure out how to do USM in image domain w/o having to convert to spectral domain (FFT)... how trivial it is! and yet it took me few hours

[delic]

This has a lot of applications.. Awesome stuff especially masking related..

[venivedi]

Wow, cool. I'm so impressed by a layer named 'clipping'

[byRo]

Originally Posted by venivedi

Wow, cool. I'm so impressed by a layer named 'clipping'

Glad you liked it.
As I remember there is an action for setting up the layer in the ten-minute tool box - then you can use it anywhere.

Rô

[palms1]

Thank you
yet again another must read tutorial, I have just had a go with unclipping and need to practice that before i have a go with something else, but there again my fingers are starting to itch ! ! ! ! ! !

[venivedi]

Thank you again, byRo. Sometimes I don't see any clipped area because of lighting circumstance, monitor setting and etc. So I really appreciated your effort.

[hpycmpr]

Thanks, byRo. Great tutorial. You mentioned "Next up: Sharpening: The true story". Is there an accompanying sharpening tutorial?

[byRo]

Originally Posted by hpycmpr

...Sharpening: The true story". Is there an accompanying sharpening tutorial?

Thanks for the nudge, hpycmpr. I knew I had written it, but I couldn't find it posted either!

Then I remembered that it was on my "to do" list when my computer got nicked. Luckily I have found an e-mail with a draft prevew that I sent to a highly-respected fellow member, so I should have it up soon.

Rô

[hpycmpr]

There are plenty of sharpening tutorials floating around, but I look forward to yours. Judging from your other tutorials, I'm sure you will something fresh and insightful.

[byRo]

OK, here you go .

Rô

[sergo]

ByRo, please tell me what kind of the file "byRo Graphics Eq.zip" and how installing it?

[byRo]

The .zip means that this is a compacted file to be opened with WinZip (or WinRar).
If you are using a Mac, sorry, bit I don't know the options there.

Inside the compacted file is the .atn file.
This is a file with a Photoshop action. You should save this, best somewhere inside your Photoshop>Presets folder.

In PS, goto the actions palette, find the little menu button and choose "Load Actions..." and load the .atn file.
After that - run the action.

Rô

[RonS]

Hi,

Just joined the forum, looking forward to learning a lot. I've tried to download byRo's Graphic EQ file, but I keep getting a screen that tells me that there is an error and asks me to log in. But I am logged in!

Can anyone help?

Cheers,
Ron

[ashphotoart]

Nice tutorial.

[ckporkchop23]

Nice tutorial and great work putting the action together. It truly helped me understand the use of the High Pass filter.

Thanks again Ro

[Stroker]

Few quick notes.

One thing that I am aware of is clipping. There is something going on under the hood and can clip in certain extremes. This only happens in very specific circumstances. I've also seen this clipping in a few other places in Photoshop (geeky tech places). I got an e-mail some time ago from someone that noticed this as well. He gets around it by doing things one way, doing them the other way, and then using ChOps to average the two. Because his fix works, I believe that Photoshop actually uses XYZ (or Lab as I originally thought, but XYZ makes more sense) as the internal colour space and converts as needed. But I could be wrong about that. At the very least, be wary of clipping when doing these things.

Another thing is that you do not have to use Gauss and High Pass. Once you understand the acrobatics, you can certainly use Median or whatever to get the bands. Median is one of my favorites because it largely respects edge transitions. You can even mix-n-match. For example, Gauss for lows, Median for mediums, and High Pass for highs.

[tepic]

This action & tutorial is one of the most useful thing I've come across. Thanks byRo!

[mistermonday]

Yes, the technique has a number of valuable applications. Further it becomes even more valuable if you use the new Apply Image High Pass technique that surfaced recently to make an accurate High Pass.
Regards, Murray

[tepic]

Murray, can you post a link to said technique? Thanks.

[Der_W]

@tepic: Here you go: http://www.modelmayhem.com/po.php?thread_id=439098

[tepic]

Danke viel!

[mistermonday]

Der W, thanks for posting the link. I did not have access to my PC for while. Tepic, you don't need to wade through the large number of posts in that thread as the most important page is the first one.
Regards, Murray

[neumero4te]

Hey works nice

[gamedonechanged]

You should get Natalias DVD as her workflow incorporates this technique.