what frequencies are?

[Isedo]

Hi all, i'm starting to hear a lor about frequencies but I really can't understand practically what we are talking about.

I saw in the Chris Tarantino webinar he has some curves present regarding high and low freq.

Please can someone explain in a practical way how to use them and what they are? Thanks

[Godmother]

Originally Posted by Isedo

Hi all, i'm starting to hear a lor about frequencies but I really can't understand practically what we are talking about.

I saw in the Chris Tarantino webinar he has some curves present regarding high and low freq.

Please can someone explain in a practical way how to use them and what they are? Thanks

Very long explanatory thread in Model Mayhem
http://www.modelmayhem.com/po.php?thread_id=439098

Debate and some easier explanation here
http://www.modelmayhem.com/po.php?thread_id=527633

[Isedo]

Yes, i red that thread but really did not understood it...
Can u please show some practical exemple?

[Godmother]

Originally Posted by Isedo

Yes, i red that thread but really did not understood it...
Can u please show some practical exemple?

There's a lot of practical samples on that same thread. I'm against spoon feeding.

Read it all.

x

[Isedo]

I have red it. All that regarding the sharpening is ok, no problem for me. But that thread does not explains what frequencies are....not for me...I mean in practical way...high pass is high frequency and blur is the low one?

[gamedonechanged]

There are plenty of examples in that thread but you only really need to read the 1st page and then from page 12 onwards.

All you need to take from that thread is that you can separate your image into 2 frequencies, 1 high which is the texture and 1 low which holds the tone. From that you can do a better job of cleaning up the imagine before you do some d&b.

[gene_spark]

Ist very easy, fine details like Hair are hight ferquencies, big things may be like Clouds in the sky are low fequencies.
In Cameras a low Pass Filter is used,....ist a better name for a blur....:-))


lg.

[Quantum3]

You have to have the experience, then you will understand the meaning. It's like in music and equalizators. You can increase/decrease the frecuencies. I'm personally wondering how to handle the other frecuencies of the spectre, the same than in music you have several frecuencies and you can edit all of them, in image is the same but wondering how to do that. If anybody can answer this, go ahead

[Isedo]

THanks so much for replies. The answer of gamedonechanged and gene_spark, in particular way, are exactly what I was looking for. Thanks so much.

Reading the Quantum3 answer I agree that is very interesting to understand that point.
In my post processing workflow I'm always using frequencies but I never knew they are called like that. I don't want to do a duplicate of the modelMayhem thread here but...this is another forum, with another people, so if you agree, we can continue this argument also here. What do you think about?

[gene_spark]

@ Quamtum3
years ago Nik had a tool an they called it ...Equalizer.
With unmask sharpening and blurring you can handel the freqencies with the radius setting..and the strenghts with the amount...if thats not enough you can Mask or use the Blend-if Slider, or you you use The Curve. All Image adjustments in Photoshop are to manipulate Frequencies from different perspectives.
@ Isedo
but i think that this topik is too technikal for me. I´m looking at a Picture and then i changed what distracts me. In Beauty retouching i think oh, these Pores are to heavy so i damped ist with D/B and thats all. Im not thinking in frequencies im not in signalprocessing with Mathematica or Math-Lab, i do retouching with Photoshop.
May be the Dan Margulis " Applied Color Theory Group" is a Yahoo Group you are interested in. There, the topic of Image manipulation was discussed on a very high and also praktical Level.
lg.

[gamedonechanged]

I think sean has even made a video to explain what is in that thread. Doesn't get more spoonfed than that guys.

[Godmother]

Originally Posted by gene_spark

i think that this topik is too technikal for me. I´m looking at a Picture and then i changed what distracts me. I do retouching with Photoshop.

Funny I also retouch with photoshop.

I disagree with you. In my first class I teach the importance of looking and understanding a picture, mentally separating the elements of the image.

Literally I say: You're not looking at an image anymore but a summary of details, such as tone and luminosity information, pixels, shadows and highlights, tone and texture. Bone structure and symmetry. Crop and composition. etc, etc, etc.

That thread was very valuable to me once I shuck the prejudice and read it because I stooped used the split all together because it was not accurate (When I used the regular high pass) and Sean actually thought me something! Now my workflow is faster and better.

x

[Jerryb]

hi ,
now i am just a laymen but this my understanding....

first.. keep in mind the word frequency is used in many ways but i believe were talking about light frequencies....

and that the thing were talking about light frequencies.... and how they can be maniulated weather to enhance colors, effect contrast, effect bluring, etc... by either blocking certain frequencies or changing frequencies or filtering frequencies (not much different than how you select radios stations on your radio!! ....

many photographers there really using frequencies quite a bit.... for example those attached lenses, your uv filter is filter/blocking those light frequencies that associated with haze, the end result the blues are bluer or your warming filters which blockes the blue frequencies and allows more of the reddish orange frequencies...

now with photoshop ... and remember were only interesteds in the display and not how they simulate (in simulating they use a lot of math...lol) !! your various tools will use frequencies...
your curves adjustment.. to me were really changing the intensity of a a range of frequencies, so that to lighten or brighten or enhance ...
your contrast type tools (sharpening or high pass filters, contrast, etc) were enhancing certain high freq's.. or your blurring tools where were effecting the low freq's ....

now have noticed the same thing over the years... nothing has really changed other than for some reason more and more the word is used to discribed things... for example... doing a hue shift... i see more and more the word frequencie is used instead of the phrase hue shift...!! oh all your doing with a hue shifting is changing the the base color frequency ....

i tried to look around for a good article on frequencies and how there used in photoshop... but extremely diffucult to find something in laymens terms...
did find this one for you and i hope it helps alittle bit , it could have been done better and more info added, but it is better than lot i looked at...
http://tech-slop.serveit.org/wiki/in...um_Frequencies

I am not sure how much help my post is ... probably there some misunderstanding on my part but that how i understand... bottom line i end up.. just experimenting a lot...lol.. to get the result i want....

Originally Posted by Isedo

Hi all, i'm starting to hear a lor about frequencies but I really can't understand practically what we are talking about.

I saw in the Chris Tarantino webinar he has some curves present regarding high and low freq.

Please can someone explain in a practical way how to use them and what they are? Thanks

[ShadowLight]

here is a visual example...

First image is 3 frequencies drawn by hand and put together, and how it looks when one of the frequency is removed.
(this is just to get basic idea of what the frequency is)


The second image is example of the actual frequency split of the composite.

Of course when someone talks about a frequency they mean frequency band. so here the frequencies are split, half of the frequencies are in one of the image, the other half in the other. When you put the images together again you get back the original image. However this way you can edit a specific frequency band leaving the other intact.

hope that makes more sense to you

[mistermonday]

OK, looks like some folks seem to think frequencies in digital images have to do with frequencies of light waves (color) and others think they are all about sharpening and blurring - neither are the case. Spatial frequencies in digital images are related to textural characteristics of an image. Fine / small radius edges represent rapid variations of lightness levels sometimes called "roughness". These are called High Frequencies and they are the fine features in an image and in the case of noise they represent the small particles of noise which are often referred to a High Frequency Noise.
Smooth areas of an image are characterized by little variation in brightness and tone and are referred to as Low Frequencies. Another way to relate to these spatial frequencies is to say that fine / small radius edges or areas can be very numerous in an image and therefore their frequency of occurrence can be high. Large smooth areas take up lots of space and therefore the relative frequency of recurrence in an image is low.
In retouching and many other forms of image editing, it becomes very advantageous to isolate the fine detail and edges from the smoother larger areas. There are a couple of tools in Photoshop that assist in isolating these "frequencies".
The High Pass Filter is one such tool. It starts at the highest frequency by looking at edges that have a radius of 0.1 pixel. The filter increases the contrast of the pixels along that edge up to the radius specified. Pixels of all edges whose radii are higher than that specified are turned to 50% gray. As you raise the radius in the High Pass filter dialog box, you reveal more and more of the image because you are allowing the lower frequencies to be contrasted and more visible. Gaussian Blurr has the inverse effect of HP. It blurs or reduces the contrast of pixels along an edge and leaves all other pixels unchanged. When you mathematically add an image that has been High Pass filtered to an image which has been Gaussian Blur Filtered (at the same radius), the result will be the exact original image.
There are a lot of threads and tutorials at RP and elsewhere, including that ModelMayhem thread, which explain some of the uses of separating images into spatial frequencies and how they can be useful in retouching and other image editing.
Regards, Murray

[ShadowLight]

Originally Posted by mistermonday

OK, looks like some folks seem to think frequencies in digital images have to do with frequencies of light waves (color) and others think they are all about sharpening and blurring - neither are the case. Spatial frequencies in digital images are related to textural characteristics of an image. Fine / small radius edges represent rapid variations of lightness levels sometimes called "roughness". These are called High Frequencies and they are the fine features in an image and in the case of noise they represent the small particles of noise which are often referred to a High Frequency Noise.
Smooth areas of an image are characterized by little variation in brightness and tone and are referred to as Low Frequencies. Another way to relate to these spatial frequencies is to say that fine / small radius edges or areas can be very numerous in an image and therefore their frequency of occurrence can be high. Large smooth areas take up lots of space and therefore the relative frequency of recurrence in an image is low.
In retouching and many other forms of image editing, it becomes very advantageous to isolate the fine detail and edges from the smoother larger areas. There are a couple of tools in Photoshop that assist in isolating these "frequencies".
The High Pass Filter is one such tool. It starts at the highest frequency by looking at edges that have a radius of 0.1 pixel. The filter increases the contrast of the pixels along that edge up to the radius specified. Pixels of all edges whose radii are higher than that specified are turned to 50% gray. As you raise the radius in the High Pass filter dialog box, you reveal more and more of the image because you are allowing the lower frequencies to be contrasted and more visible. Gaussian Blurr has the inverse effect of HP. It blurs or reduces the contrast of pixels along an edge and leaves all other pixels unchanged. When you mathematically add an image that has been High Pass filtered to an image which has been Gaussian Blur Filtered (at the same radius), the result will be the exact original image.
There are a lot of threads and tutorials at RP and elsewhere, including that ModelMayhem thread, which explain some of the uses of separating images into spatial frequencies and how they can be useful in retouching and other image editing.
Regards, Murray

I'm trying to simplify it as much as possible and show some visual example...
I guess some people have a hard time understanding the idea of frequencies and how to visualize it. Do you think in this case saying "mathematically adding HP to blur" will be much different than reading the threads on MM?

If someone can come up with simple visual example that breaches the "math" gap I would like to see it.

[markc78]

I fully recommend this technique especially for image clean up however I recently had an test run with a high-end retouching studio/agency & applied this technique thinking it would impress but in fact it had quite the opposite effect with the owner concluding that I was far too technically minded & not in touch with the natural image enough which he felt was the purer approach.... needless to say I didn't get the position ...but I couldn't have worked in that kind of enviroment anyway....
Still don't understand people like that , Ps is a technical tool & retouching is not some precious art ... & I've since encountered various hi-enders who practice all sorts of tech'y tricks such as applying solar curves etc to expose the image in different ways, & for me this forms a natural part of the retouching process... but some people are too precious too accept such things... anyway thought I'd share that experience...

[ShadowLight]

Originally Posted by markc78

I fully recommend this technique especially for image clean up however I recently had an test run with a high-end retouching studio/agency & applied this technique thinking it would impress but in fact it had quite the opposite effect with the owner concluding that I was far too technically minded & not in touch with the natural image enough which he felt was the purer approach.... needless to say I didn't get the position ...but I couldn't have worked in that kind of enviroment anyway....
Still don't understand people like that , Ps is a technical tool & retouching is not some precious art ... & I've since encountered various hi-enders who practice all sorts of tech'y tricks such as applying solar curves etc to expose the image in different ways, & for me this forms a natural part of the retouching process... but some people are too precious too accept such things... anyway thought I'd share that experience...

I guess it's best is to deliver the final result without saying how it was made.

[TommyO]

Murray,
Well stated, and appreciated. Thanks to Isedo for making you write it.

Shadowlight,
Good example images, which will be helpful to many.

Natalia,
"looking and understanding a picture, mentally separating the elements of the image." I agree with this also, but it seems to come easily to some and hard to others.... left brain vs right brain thing. I have a deep appreciation for the more artsy individuals, since I am lacking in that area. (You seem to have a nice blend of both by the way.) There seem to be many excellent retouchers, photographers and artists out there that simply are not concerned about the technical aspects as much.

[Godmother]

Originally Posted by TommyO

There seem to be many excellent retouchers, photographers and artists out there that simply are not concerned about the technical aspects as much.

Cool, just don't say something technical can't be part of an artistic process

Or I'll let you have it

Thanks for the compliment.

x

[TommyO]

Originally Posted by Godmother

Cool, just don't say something technical can't be part of an artistic process

Wouldn't hear that from me... I come from a primarily technical background.

Whereas, one member of my family is very artistic, yet really shy's away from the technical. Her photographic and painting skills are excellent without it. As many of us in my/her generation that span that time from non-digital to digital, there were times when things such as spatial/frequency separation were done by feel, not by the numbers. And today, trying to get her to do it by the numbers is not practical. Yet, I prefer to always be learning and blending technology with the arts.... which is why I said what I did about your philosophy.... I like it....

[MariusX]

Originally Posted by Godmother

Very long explanatory thread in Model Mayhem
http://www.modelmayhem.com/po.php?thread_id=439098

Debate and some easier explanation here
http://www.modelmayhem.com/po.php?thread_id=527633

These threads are fascinating, Thanks Godmother!

[Isedo]

Originally Posted by gene_spark

@ Isedo
but i think that this topik is too technikal for me. I´m looking at a Picture and then i changed what distracts me. In Beauty retouching i think oh, these Pores are to heavy so i damped ist with D/B and thats all. Im not thinking in frequencies im not in signalprocessing with Mathematica or Math-Lab, i do retouching with Photoshop.

I agree with you, i thought that knowing all this math stuff is important but as you, i work with photoshop for years and never used math...I have the same workflow as yoursbut i think knowing these think can improve our method

Thanks for replies

[Isedo]

Originally Posted by Godmother

Funny I also retouch with photoshop.

I disagree with you. In my first class I teach the importance of looking and understanding a picture, mentally separating the elements of the image.

That thread was very valuable to me once I shuck the prejudice and read it because I stooped used the split all together because it was not accurate (When I used the regular high pass) and Sean actually thought me something! Now my workflow is faster and better.

x

Sorry can u say which class u did and who is Sean u are refering to please?
Thanks

[Isedo]

Originally Posted by Jerryb

I am not sure how much help my post is ... probably there some misunderstanding on my part but that how i understand... bottom line i end up.. just experimenting a lot...lol.. to get the result i want....

Thanks for your kind answer, I'm going to read the link.
Thanks to all now is more clear for me what frequencies are...we use them all the time, I just never called them in this way.

[Isedo]

Originally Posted by mistermonday

... Spatial frequencies in digital images are related to textural characteristics of an image. ...

Many thanks Murray and ShadowLight for your time, great explanation. Now is really all cristal clear!

Martin