Week 2: Exercise 4 - Wreath

[leeharper_admin]

I'm not totally sold on this correction - but it is the best one I managed. I think that I'll have another go at it in a few weeks, when I'm more on top of things...

The aspects of my correction that I don't really like are the flowers in the centre of the wreath (inside the yellow ring), the brick wall on the left of the picture seems too magenta, and the red leaves of the tree behind the wall. I'm quite happy with the detail I've pulled out of the shadows though  :).

I only worked on this in CMYK, but I tried Light, Medium, Heavy, and Maximum GCR (just for the practice - I know that the instructions only mentioned Medium and Maximum). I am only going to post the Maximum GCR version, as I think it's much better than the other three.

I followed the instructions, but adjusted each channel - and tried to boost saturation by pulling the shadow endpoints of the CMY curves to the left, as Greg G did in his CMYK merry-go-round correction. Maximum GCR gave me more control. I found in the other attempts that I couldn't lighten the shadow by lightening the Cyan quartertone very much without the colour of the treebark looking bad. I found that Maximum GCR gave me more leverage.

One problem I faced was that when I'm in CMYK the Hue clocks were not working. I've just noticed that if I create the Hue clocks in another colour mode and then switch into CMYK I can sidestep this bug - but when I worked on this I used the standalone Hue Clock application.

Lee.

[ggroess]

Lee,
Are you also using the Color Worm?

It can help you zero in on the parts of the curve to adjust. 

In CMYK the shadows generally live in the K channel.  Even if there is color in the shadow the primary place to start for me has always been the K channel.  The logic goes like this....If you were printing the image on a press you would have to use 100 "units" of the ink to get the density you could have with 25 "color" and the rest as K until you match the desired color.

That's the whole reason for the K Shadow density without ink density...
Greg

[leeharper_admin]

The logic goes like this....If you were printing the image on a press you would have to use 100 "units" of the ink to get the density you could have with 25 "color" and the rest as K until you match the desired color.

I'm probably being really dense, but I find that explanation a bit vague. Would you mind breaking that down a bit more for me (my brain feels a little scrambled this morning  ;)).

Oh - and I'm not using the color worms. I've yet to figure them out...

Thanks - as always - for your patience and guidance,
Lee.

[ggroess]

Ok...let's try this....

Let's start with the GCR...GCR is Grey Component Replacement.  This is the amount of gray in any given color. Think of it this way;  If a color has an RGB value of say 120,100,90;  you could say that it really has a value of 35,15,5 with a GRC of 85;  we don't do this because RGB is not suited for this but I hope you get the analogy.  Essentially if you take out equal amounts of each color you are removing "gray" since a neutral color in RGB is equal amounts of R,G,and B.

We have different GCR values based on the paper, printing press and ink chemistry values; some inks have more transparency on different papers so you have to use more K to make the tones you want.  This is what makes CMYK so intricate.  At the end of the day it is all about getting the most ink onto the page as possible without making a total mess of things...Dot gain is a big part of this process...as are many more variables.

Now...

In CMYK we are really using ink on paper.  This has tight limits; People write books about this so bear with me...
If I have a piece of paper that I want to print on a press and my printer tells me that the ink limit is say 100 units....I have to keep the CMYK values under that 100 or risk having the paper and ink combination mess up the final print. 

So, I manipulate the CMYK values so that the combination of CMY Plus the K is 100 or less.  I also know that the colored inks are expensive....so I want to use only the maximum amount of color needed to produce the image correctly.  The rest I fill in with cheaper K. 

Ok...so what is the price of china tea then....

CMYK is a great tool for color correction because it is the subtle feather brush in comparison to the hammer that is RGB and the sledge hammer that can be LAB.  It is also your best friend in Masking because it gives you a very nice channel to find luminosity type masks.  Most people do not really get CMYK until they think of it this way...

RGB is like theater lighting you mix the lights together and if you have all of the right values and they are bright enough you get white light.  255,255,255
CMYK is like painting...you mix the colors together and you get black  100,100,100 but...because ink has transparency you need K to complete the "blackness"

The color worms are really handy tools for you...open an image in CM and set the color space to RGB.  Choose a nice green or red area and place the mouse there.  Let go of the mouse...movement makes it hard to see what we have going on.  On the RGB channels in CM you will see a segment of the curve highlighted in the color represented.  This is the area of the curve that would have to be adjusted to effect the point under your mouse.  It will become more important later in the course when we get into adjusting color contrast. 

There is also a curve highlight command. 
I'll go into that more later but is shows you a mask of the areas effected by any point you have set on the curves.  If you click on a curve like you wanted to make an adjustment, with the highlight command "on" you can see what other areas of the image are effected by that point on the curve.

Keep asking questions...I will hopefully keep giving answers...
Greg

[ggroess]

Lee,

Remember that you have to think in inverse color in CMYK.  If the red bricks are a problem you have to remember that Red is really M and Y so you have to adjust both.  The Yellow channel is where your issues lie.  See Screen shot and ACV file.  If you apply my ACV to your posted image you will see what I mean. 

1) Highlights...The area near the top of the wreath has a tiny bit of green in it...C + Y..so on the highlight ends of the curves I have removed some of it..see the hue clocks on the screen shot.

2) Bricks, and red leaves, you worried about the color a bit.  again the redness is found in the yellow channel.  Counter intuitive but real...I'm not so worried about the leaves as I am the bricks...the leaves are sort of believable as a red orange... if it really bother you take a second pass at the leaves after applying the changes.  When I tried to adjust them it messed up the bricks and I liked the bricks too much to lose the adjustment.

3) Overall, I think a little K channel work helps the image as well...

Greg

[leeharper_admin]

Thanks so much for that explanation Greg, it really hit home. Your comment about needing to add K to CMY to create proper blacks because the CMY inks are slightly transparent sheds light onto something that I've never understood before - and makes perfect sense - another lightbulb  ;D

I've read that to create a neutral in CMYK you need to use equal M and Y, but higher C. Is this because Cyan is more transparent?

There is also a curve highlight command. 
[It] shows you a mask of the areas effected by any point you have set on the curves.  If you click on a curve like you wanted to make an adjustment, with the highlight command "on" you can see what other areas of the image are effected by that point on the curve.

This sounds great! I'm logged into my Mac at the moment, so I've not played with this yet, but for me this could well be CMs killer feature. Everything else it does is cool, but this is fantastic!

Thank you again for posting those curves (and the Red=M+Y explanation). Super helpful  :) I will load up the curves when I'm logged into Vista.

Best regards,
Lee.

[ggroess]

I've read that to create a neutral in CMYK you need to use equal M and Y, but higher C. Is this because Cyan is more transparent?

Yes that is the generally accepted explanation.  It is also why there are so many different CMYK color models out there the inks and press and paper surface variables make the combination really interesting...

Greg