LAb color space

Hi !

This is to those of you comfortable working in lab color space as elaborated by Dan Margulis in his Canyon con....!

i actually need guidence in the step wise executing the --one channel replacement [b channel for example] by a copy of another [a channel for example] of the same image file as shown in chapter 10 of the above mentioned book!

I am unable to do it --Either I have understood something wrong or not at all!

Thanks for any responses that may come!

Are you talkin Photoshop?

I manage to do that as follows:

• switch to LAB (I suppose you can do that)
• go to the channels pallette
• switch off all channels exept the one you want to copy (say B)
• select all (Ctrl-A) and copy (Ctrl-C)
• switch on the channel you want to copy TO (say A)
• switch off the other channel
• click on the thumbnail of the channel you want to copy TO (say A)
• paste (Ctrl-V)
• switch on all channels.

By 'switch on/off' i mean the visibility (eye)

Also funny:

• switch off all channels exept the one you want to (say A)
• click on the thumbnail of that channel
• press Ctrl-I to invert it.
• switch on all channels.

Now I will think of a way to actually USE this knowledge...

Works for me.
--
All in my humble opionion of course!

If I seem to talk nonsense or you can't understand me, it's probably my English

for the change of the blue car to the yellow/orange color.

1. make a copy of the RGB file

2. convert one copy to L*a*b

3. make a layer copy

3. open channels and click on the letter "b" this selects the a channel and deselects
the others. you can then click on the selection square next to Lab channel
name. This returns the display to full color.

4. go to the menu bar and choose image, on the pull down menu choose apply
image.

5. the Channel designator should read "b", change this to "a"

6. For this technique the blending mode should read normal ( other techniques
will require different modes ).

7. Opacity should read 100% ( Other techniques may require different
amoounts ).

8. Click the OK button. You have now substituted the "b" channel with the "a".

got the book did not see what you are talking about
email me with page and infor and will try and help
may be tomorrow

thanks Adriaan and tom60634 for responding !

Yes suggestions from both of you were very useful and they helped me!

Adrian! this step helps in changing colors as u know already !

however this effect of color change is not something that one may seek frequently

But I was finding frequent reference to this step [ change one channel for another]in the succeeding chapters where the author refers to this step in achieving other effects that one may be keen to achieve rather than a color change !

Another similar reference is channel blending [i.e. seeking to blend channel a to L channel in order to emphasize contrast and color in the green foliage ]
How does one achieve this ?

So far I have been using the apply image window for the channel blending --but the effects do not come !probably I am in error !

But if as tom60634 suggests usage of the apply image ...window for the channel replace ment how does one do the channel blending ?

To Tom Bennet----My query was with reference to last 2 pages of chapter 10!The author ende the chapter with the technique of replacing one color for another accross the channels ! Later the author makes frequent references to the steps of channel replacements and channel blends as quick moves to enhance certain colors of intrest like greenery of foliage or color of the sky etc!

I'm not good in them LAB-adjustments (perhaps I should read (and practice) the book you mention )

But there's always another road to Rome...
What I would do to lighten (or darken) foliage (greens) is this:
In non-lab mode (doesn't work in LAB).

Make a new adjustment layer, 'B&W', adjust the greens differently than other colors, set blending mode to 'luminocity'.
--
All in my humble opionion of course!

If I seem to talk nonsense or you can't understand me, it's probably my English

In case you might be interested in this, but may not know about it, Dan Margulis teaches several online classes at kelbytraining(dot)com. They all deal with working in LAB.

I have watched all of them and although they are still quite advanced, I found it easier to learn by watching him work and talk, then by reading. He works thru many images so that you get to see how he handles different problems. In the videos, he also mentions several things that he has learned since writing those books.

--
Chandra

OK in these pages he is first using curves adjustment layer to flip the colors by making major changes in the sliders moving top to bottom on one side, doing the reverse on the otherside, page 213. create as many unaltered dubbed layers plus one more as you are going to need. add a curves adjustment layer to each one of these layers. do this by clicking the black and white circle at the bottom of the layers palette.

turn off (click eye) on all the but one adjustment layer. Start at the first one above the first layer without an adjustment mask added. make curves slider changes to the area you want such as trailer. turn this layer off turn next layer on.next layer change car turn it off last layer on , last layer change grass. Here is where he does it different than I do he uses the blend if palette. that is the first icon bottom layer to make slider changes. This never works good for me and I still have to do touch ups. I am a layer painter so I just go to the layer I want and paint with a black or white brush on each layer to let the lower layers show through. Tip on this the layer mask can be inverted to black by holding ctrl and letter I then all changes disappear and return when painted with a white brush. Saves time when you are change a small area like the trailer. The picture of the blend if box palette is not completely showing in the book. He as cut out only the channel and slider portion of that palette

re: But I was finding frequent reference to this step [ change one channel for another]in the succeeding chapters where the author refers to this step in achieving other effects that one may be keen to achieve rather than a color change !

Another similar reference is channel blending [i.e. seeking to blend channel a to L channel in order to emphasize contrast and color in the green foliage ]
How does one achieve this ?

So far I have been using the apply image window for the channel blending --but the effects do not come !probably I am in error !

But if as tom60634 suggests usage of the apply image ...window for the channel replace ment how does one do the channel blending ?

One also should remember that there are blend modes in the layer panel.

When you accomplish your channel blend ( it should be done on an additional layer of course ) you then move to the layer panel and and choose your layer blend there.

It seems Mr. Margulis is fond of Mutlply, Overlay, and Hard Light for extremely increasing color and contrast effects and then dialing down the effect with the panel's opacity slider.

To Adriaan--The first suggestion that you made showed how to copy one channel [like channel a ]on to the other channel [like b or L]! Thanks very much!

In your second post I was wondering how u will adjust the green in a B&W adjustment layer!

Thanks to C Willis for the information on the classes that Dan Margulis gives --I truely was not aware of it!

Thanks to Tom Bunnett for sharing his variation on achieving color emphasis in the different objects by using a seperate layer for each section/portion of the original image ! Yes sir I do agree with you that your method [TO MY MIND]is easier to apply !

To tom60634 --the apply image window is very precise and I did use it as you suggested !

However there is a check box saying mask !If I tick it a second half of the same [apply image ] window opens up with more options [...I am with CS3]--A title to it says destination document --Does this lower half of the, apply image window , cater to working with the MASK of the adjustment layer ?I mean this lower half opens up even if I am working with a single layer [background layer]

The mask is used to help control the blending.

If you look at the channel selection device, you'll see that you are able to mask out the lightness, "a" or "b" channel from your apply image blend.

You'll also be able to invert any of these choices. I hardly use it, but it's there if you find a need for it.

Using the layer mode provides you with the ability to provide your "apply image" layer with a mask that is more powerful and easier to control.

It wasn't until I subscribed to Kelby Online for a couple months and watched all 6 hours of Dan's videos that I finally got what he was saying. I recommend subscribing to it more highly than any other online tutorial site, including Lynda (dot) com.

I also loved the videos by Ziser and Joe McNally, which you get access to.

Honestly, go watch them and then practice. A workshop tutorial with Dan used to cost $3000 Cdn, so the $30/month is well worth it.

cheers,
Chris

drpankajshukla said:

To Adriaan (...)

In your second post I was wondering how u will adjust the green in a B&W adjustment layer!

Click to expand...

The B&W adjustment layers gives SIX sliders to control which color contributes in what amount to the luminocity of the result.

Therefor you can choose to set the GREEN slider to the right and the other to the left (or something).

Try it.
--
All in my humble opionion of course!

If I seem to talk nonsense or you can't understand me, it's probably my English

Thanks to all of you for responding in order to help me out with my query!

Yes I am clearer now than before !