Can you help me clarify something

[rit_romey]

Hi

I am a beginner and have started playing around with different techniques in photoshop. I am mostly a

b/w enthusiast also. I have a question for you. For adjusting tonalities in an image we generally use

global and local enhancements like curves and unsharp mask (with high pixel radius and low amount). So

if these two can be considered as prototypes of global and local where do you think dodge and burn fits

in. Can it be thought of as mid-level enhancement..kind of like between local and global? I ask this

because this helps me to better remember stuff and explain it to someone else. I know there probably isnt

such mid level adjustment but by discussing with you guys I think my knowledge will be refined. Thanks

alot.

 

Rit

[bryantan]

It's global...except where it is not. To talk about burning and dodging, you must also talk about masks. If you don't, you are merely adjusting the exposure of the entire image.

[emre]

Unsharp mask is not local unless you use a mask. By local we generally mean manually masked.

[will_hammond]

The Dodge and Burn tools are clearly local as the brush size of each makes them selective to a specific part of the image

[rit_romey]

I remain muddled...though I take complete responsibility...hahhaha.

[jerryrock]

Adobe Press - Photoshop CS3 Classroom in a Book

[jimstrutz]

Curves and USM are global because they apply to the whole image. Dodge & burn and generally local because they usually apply only to local areas of the image.

[ethervizion]

There is a confusion/disagreement here as to what the terms local and global mean. Some people use it to literally mean whether all the image was affected or only part (e.g., through masking) -- this would make curves and USM global.

 

However, there is a more subtle definition which refers to whether the operation takes local context or neighbourhood into consideration. In this context, curves are still global -- it's a global mapping of values x->y. In other words, a certain mapping of one pixel value to another is the same, regardless of the location of that pixel in the image. However, here USM is local -- the mapping is different depending on the pixels location relative to structural elements in the image (e.g., edges). In other words, the mapping may be for values x->y in some part of the image and value x->z in another part of the image.

[jacopo_brembati]

Karl, I agree with you: <br>

Global and local <b>"enhancements"</b> depends on performed action: <br>

- an S-shaped curve performs a global contrast enhancement.<br>

- USM performs a local contrast enhancement. <br><br>

"Global and local <b>"editing"</b> is for all the image (global) or for a selected region (local).

[emre]

USM only performs "local" contrast enhancement if you use a small radius. I prefer the terms microcontrast and macrocontrast to distinguish it from local/global masking.

[rit_romey]

I think USM is still local if you use a large radius because it adjusts between adjacent pixels

while s-shaped curve doesn't care about nearby pixels...it sees pv as is not in comparison to

its neighbourhood....the pixel radius just tells you how localised are you...no matter how

much you increae the radius you cannot cover the entire picture(not even a microfraction of

it) in which case it could have been global....I completely agree with karl.

[emre]

What do you mean? Set the radius to the length of the picture and it covers it all right.

[jimstrutz]

And I still consider USM to be global because it effects areas all over the image. No wonder *you guys* are confused. We don't use the same definitions. :)

[will_hammond]

This USM is local is absolute nonsense, the fiter applies to the entire image, making it global, unless a selection is active. It applies to the entire image based on the values entered into the filter dialg box but the entire image is calculated across. Even if masked it still applied to the entire image, making it global, the mask simply hides the effect in a given layer, but the effect was global none the less.

[ethervizion]

Will, just because you don't understand a definition or use a different one, doesn't make it nonsense. Image processing is my area of research (as in algorithms, not dinking around with consumer software). In calculating an output pixel value, USM takes into account the values of neighbourhood of pixels, making it a localized operation.

[emre]

Except when you use a large radius and the neighborhood becomes the entire picture.

[rit_romey]

My version of CS3 is showing that the radius can be set to a maximum of 250....exactly which

version can take the entire picture as a neighbourhood?

[will_hammond]

Excuse me Karl, but I was on the development team of Photoshop v 1.x. I have been on the Alpha/beta team of every version since .087a I know very well what the definition is. The calculations are done across the entire image. The radius simply tells how far from a particular pixel that particular pixel will effect other pixels. It still looks at every pixel in the image to see if it will create an effect or not.

 

Will

 

Adobe CTI Photoshop

 

(in case you don't know what that is "Certified Training Instructor Photoshop")

[ethervizion]

Will, those are nice credentials, but it doesn't change the fact that we are operating under different definitions. The definition you are operating under may be standard "Adobe speak" but there is a whole other world out there... We can agree to disagree, but there is simply no need to use language that dismisses the world outside yours.

[will_hammond]

Whatever. Being that we were discussing USM which is part of Photoshop, an Adobe product, I guess I'm out of line using "Adobe speak" since this IS an Adobe program? I think not. Different definitions, absolutely. I didn't write Photoshop nor USM, I simply pointed out how it was defined by Adobe. What is "outside my world", in this instance Photoshop , is irrelevant. It's not intrupation, it's fact. Sorry if my use of the word "nonsense" ruffled some feathers. It wasn't intended to. Voice inflection doesn't come across in text :-)

 

BTW, I found your comment about how "image processing is my area of research (as in algorithms, not dinking around with consumer software)" equaly dismissive. I guess we're even. I included my credentials, which you equally dismissed, just to show that I was qualified to comment on the " Adobe Speak" nothing more :-)

 

Pax

[Tim_Lookingbill]

Heck, never mind about the use of the word "nonsense"-what the hell is "intrupation"? Is

that Adobe speak, too?

 

I realize Photo.net was founded by MIT alumni, but some of us here have only a high

school education, and may have been dropped on our heads as a child.

[will_hammond]

Let's call that a typo :-D My reply was done on a cell phone LOL

 

Pax

[rit_romey]

USM------------Local (image processing-wise) & Global( Image extent-wise)

 

 

Dodge & Burn----Global(image processing-wise) & Local(Image extent-wise)

 

 

Curves----------Global(image processing-wise) & Global( Image extent-wise)-

 

keeping in mind that all image extent-wise global tools can be thought of as local if

masking is used. Thanks for all your contributions.

[Tim_Lookingbill]

See, everybody can sound like an expert on the web with decent communication skills.

 

It can get you to think words like "intrupation" are legitimate when all it was was a typo.

 

Doh! Fooled again!

 

Thank God, Will has credentials. I was beginning to think I was an idiot for knowing what

intrupation meant.

[Tim_Lookingbill]

Correction...that's NOT knowing what intrupation meant.