RGB CMYK LAB and Dan Margulis !

[Quantum3]

Originally Posted by Markzebra

Yeah you have to be very careful with LAB, its very destructive if you use it on 8 bit images and convert those straight back and forth. This process compresses the color information into a very small area of the A and B channels. One way to minimise this damage is to convert your image to 16 bit then convert to LAB, do your edits and convert back. Another point that Margulis for some reason took many years acknowledge, is that a lot of the edits achievable in LAB can be done on the original RGB or CMYK document using Blend modes and luminosity/colour calculations. Its not always necessary to damage your file by converting to a different mode.

Margulis is a great teacher, but he has never been great a technician and the folks at Abode have had a few problems over the years with this

Hey Mark, I was missing your comments. What are you doing lately?

[katheo]

Thanks mistermonday for your help. I will do the conversion back to RGB before each print. And, I will resample down to 240 and see whether I notice any difference in the printout.

[jeno]

Hi,

I am new here, after reading all your comment. I am wondering if this is what I should be looking at if i am doing color correction for print/press?

I am doing color correction and a little bit of retouching for various printing process such as flexo, offset, gravure...etc. I am working with CMYK images most of the time. Since I am new to this industrial (print & color correction), can somebody please point me to the correct direction where/how to began and go beyond that.

I have a stack of images on my desk waited for me to be color corrected (some with color target, some without color target), since I have no idea what am I doing and what I am looking at. I doubt that I won't get it done in time!

Thanks

[Crapaud]

Hi, Jeno, and welcome to the forum.

Dan's book "The Classic Guide to Color Correction" is mostly aimed at correction for print and almost exclusively for litho. It's a great, but in-depth book and much of it will be beyond a newbie to PS. Generally, I'd recommend getting to know the tools and how and when to use them first, but I reckon that you'll get a lot out of the first few chapters. I'd forget what's discussed above and just work with the book from the start.

Good luck with your work.

[jeno]

Thanks Crapaud.

Is this the book you mention? "Professional Photoshop: The Classic Guide to Color Correction (5th Edition)" ?

Thanks

[Ice Imaging]

The one struggle I've had with Dan Margulis is staying with him long enough to sort out whatever technique he is explaining. You get three pages of Dan for every one page of technique if you know what I mean. Entertaining for sure, and the techniques are usually worth it, but man do his books ever require a box of highlighters, a note pad, and a gracious attention span. :-)

[Crapaud]

Originally Posted by jeno

Thanks Crapaud.

Is this the book you mention? "Professional Photoshop: The Classic Guide to Color Correction (5th Edition)" ?

Thanks

Yes, that's the one, Jeno.

Ice Image, I know what you mean, it could be tough going a lot of the time, but well worth it IMO. I've just read the blurb for the latest edition and it seems that he's addressed it along with new techniques and problems. I'm almost tempted to buy it myself as I've got the Prof Photoshop 7 edition.

[andrewrodney]

Originally Posted by Ice Imaging

The one struggle I've had with Dan Margulis is staying with him long enough to sort out whatever technique he is explaining. You get three pages of Dan for every one page of technique if you know what I mean.

Boy, do I ever!

[jeno]

I was watching a presentation by GretagMacbeth and come across a term called "L*C*H*. I would assume L*A*B* that they mentioned would be the same as what have been discussed here. Does anyone know LCH is or does it covered in Dan Margulis book?

Thanks.

[mistermonday]

Originally Posted by jeno

I was watching a presentation by GretagMacbeth and come across a term called "L*C*H*. I would assume L*A*B* that they mentioned would be the same as what have been discussed here. Does anyone know LCH is or does it covered in Dan Margulis book?

Thanks.

L*C*H* stands for Luminance, Chrominance, and Hue which is quite different from the L*A*B* model.
Regards, Murray

[andrewrodney]

LCH= Luminance, Chroma and Hue. Is from the old LinoColor scanner days, a variant but not a direct numeric scale as Lab. Similarly we see HLS (Hue Luminance Saturation) in Lightroom and other applications. Actually LCH and HLS are a bit more intuitive systems to teach and learn (aStar and bStar isn’t)

[jeno]

I guess learning LAB would be enough than?

[John Wheeler]

Hi Jeno
I personally would concentrate on learning the color modes that are supported by the software you use. IMHO

[andrewrodney]

Originally Posted by jeno

I guess learning LAB would be enough than?

Learn to do what?

Since Lab is a direct mode you can convert to (I find the use questionable) and Lab output values are available in RGB/CMYK color mode, while LCH and others are not, yes. It would be useful to be comfortable with the scale depending on what you hope to accomplish. But the same is true for say RGB.

These are just numeric values. Much depends on what you need to do with your images, where they came from (their color space and condition) and ultimately what you hope to accomplish. IMOH, Lab has been over sold as some kind of color model of the month. I use it a LOT for what I think its really good for (color analysis when linked to what is known as deltaE). For image editing, not so much. Its useful no question as are other color models. I guess I’m saying, don’t buy into it as some magical system, its good for some tasks, not for others.

The first thing to learn about Lab is its not an acronym (nor is raw) <g>.

[jeno]

Thanks andrewrodney & John Wheeler,

Retouching images to suit various printing process (flexo, gravure, offset, letterpress, silkscreen...etc) is what i am looking at currently. I guess it is Important to know how to "see" / "read" color before retouching it.

The more i read through the forum the more i doubt that i am looking at the wrong place. I need images to be printable and "print nice" instead of "look nice".



Thanks.
J

[andrewrodney]

Originally Posted by jeno

Retouching images to suit various printing process (flexo, gravure, offset, letterpress, silkscreen...etc) is what i am looking at currently.
J

Those images are in an RGB working space or already in some kind of output colors space (CMYK for those processes)?

[jeno]

CMYK most of the time.

[andrewrodney]

Originally Posted by jeno

CMYK most of the time.

Then you are working in the output color space. The conversions have been made. Lab is questionably useful at this point.

[jeno]

Any suggestion what should i be looking for?

[andrewrodney]

Originally Posted by jeno

Any suggestion what should i be looking for?

A well calibrated and profiled display for one. If the images are converted to an output color space (and by who and how well), one would certainly hope nearly all color and tone correction was done long before the conversion. You’ll have to describe more about your workflow to go much father.