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RGB Curves or, "Something Happened On The Way To Purple"

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This tutorial is available as a PDF. Click here to view or download the PDF


Curves – RGB or, Look What Happened On The Way To Purple!

RGB Curves is like mixing colors on a palette.

I will be discussing mainly "Primary Colors" and varying shades of them. With "Curves RGB" virtually any color known is achievable, all it takes is understanding the basics and playing around with the settings while you watch and learn how each change effects the original.

Open a new file of any size you prefer. We will only need a small area for a single circle or rectangle.

(I have drawn a red circle on the base layer and selected outside of it with the wand and inverted the selection with "Contl +I")

If you start with a red circle let's say, then red is the "controlling color" as I call it The color you will be changing or effecting in other words. Had you drawn a green circle, green would be the "controlling color". This is important because what you start with in your selection is what will be effected colorwise, the jumping off point as it were. And, black let's say, is very different from red with the same changes applied as we shall see later.

Now, go to "Adjustments – Curves" and then go to the tab and select "RGB" and have only the blue box checked.

1 2

Slide the right side all the way down to the bottom and you will see that nothing happens. Because red, being a primary color has no blue in it to be removed. (nor green either)


Now, put the right side of blue back to the top and go to the left side at the bottom and slide it up a little bit at a time. You will notice the red circle getting more pink (lighter red), why? Because you have added blue to your red which depending on amounts will make red varying shades of pink.


Do the same with the green, what do you get when you mix green with red? Depending on amounts you get colors from orange to tan, to yellow at full green (full green = left side slid all the way to top).


Now, have only the red box checked and slide the right down in incriments and see what happens. Yes, the red gets gradually darker until it's black, why? Because we are removing the control color of red, and the absense of color is black, or color #000000.


Slide the right red down and the left blue up, what are you doing? You're taking away red and adding blue which of course gives you shades of purple because now you have more blue than red. More red than blue = pinks (magenta I think it's called) more blue than red = purples and lavenders


Remember, the left side of the bar adds color to the original, the right side takes it away if it is there to take. To see this, draw a black circle and make it your selection. Now, open Curves and go to RGB and leaving all boxes checked, slide the right side to the bottom. Nothing happens because there is no color to remove.


Now, go to the left side and slide the bar up in steps and you will see the circle getting lighter until it's finally white, why? Because you are adding all colors to it and white is an equal blend of all colors.


Play around with it and get familiar. There is so much more that "Curves" can do for shading and blending or "tempering" colors. Just get a good grasp of the basics first:

The beginning selected objects color is the "control color" that you effect with your adjustments.

Right side down - takes away color if it's there to take away.

Left side adds color of selected box

(NOTE – In general, the left side of the bar will only add in colors other than the "control color". If your circle is red it will add blue or green if you check those boxes, but not red because red is already at full intensity "255" on the right side. If you have lowered the right side, you cannot "add" it back by raising the left side.)

I have been asked to expand on this so I will give it a shot. I am not an engineer nor a programmer so I am likely to be off on terminology, all I can do is explain it the way I understand it.

Now, tired of circles, me too so let's have a rectangle.

And, let's talk some more about black because it's unique for it's "absence" of color. If you draw a black rectangle (on it's own layer this time so we don't have to keep selecting and inverting) and open the Curves command and go to RGB you will see (as usual) that all the bars on the right are at the top.


This is a bit misleading because you would think that you could slide the right down and make a change to the color, but you can't. There is no color to effect in black. You can only go to the left side and ADD color, be it red, green, blue, or combinations.


Think of the "Curves RGB" as a painters color palette and all the colors in their full spectrum are there to pick from.

NOTE: Remember, you are mixing colors and the same settings will not give you the same results. It is all dependent on what you start with, as well as what you do.

Try this; draw a black rectangle if you don't already have one and open "Curves - RGB". Now uncheck the red box and leave both green and blue checked. Slide the left side of the bar up mid-way and you will see that adding green and blue to anything that begins as black will give you teal or varying shades of teal.


Now, please humor me and close the Curves window and click the rectangle command in the history window twice so you are back to a blank canvas and then draw a red rectangle, open "Curves RGB", uncheck red, leave green and blue checked and slide the left side of the bar up mid-way. Oh look, you get pinks, why? Because your starting from a completely different "control" or base color this time, red. And adding colors to red is completely different from adding colors to black, or blue or anything.


Also, if you continue to slide those green and blue colors to the top, you will see that the rectangle turns white, why? Because you have just added the full value of all the primary colors red, green and blue, and an equal blending of all colors is white. (remember, we stsarted with a red rectangle and red was at full value already.)

And, at any place along the way you can uncheck one of the boxes and which ever one you leave will shade your selection with more of that color as you slide to the top. Want more blue than green, leave blue checked, or vise/versa.

Okay, one final exersize and example. On the "Background Layer", make sure it's white and set your line weight to 25, select red from the color wheel and draw a short, vertical line in red. Now select green from the color wheel and draw a short vertical line next to the red one. Now, do the same with blue. Place a rectangle selection around the lines, we want a bit of white but not necessarily the whole page. Your drawing should look like this:


Now, go "Adjustments – Curves" and select the RGB tab as before. Leave only the red box checked. Slide the right side down to near the bottom and you will see this:


Can you see and explain what is happening to the colors now?

Lowering the red on the right causes something very strange here. It effects the white background as it should, it removes the red and leaves us with a blue and green combo that gives us the light aqua color we see. BUT, notice that both the blue and the green are unaffected. They look a little different but that is from the change in the surrounding background, the colors themselves are still just blue and green.

To prove this, cancel out of "Curves" and then reopen it. Hit reset to make sure all is back to normal, then uncheck the red and green boxes leaving just blue. Slide the right side of blue down. What do you see? Go ahead, we'll wait. Hey! You in the back there, pay attention!

Have you got it yet? That's right! The blue is being taken from the white and the blue, making the white more yellow because why? That's right, we're leaving the red and green in the white and red and green make yellow. And of course the blue is turning black because we're removing the blue from it. But the green and red are unaffected. Now why is that? Because blue is the chosen color, white is a blend of all colors, and red and green are basic, primary colors unaffected by the removal of blue. You can see this in the picture below:



Luminosity is exactly what it's name implies – light. If you have a red selection and throw some light on it it's going to lighten up and look pink, just as if you took a flashlight and shone it against red construction paper. the area with the main focus of the beam of light will look anywhere from shades of pink to absolutely white depending on the intensity of the light.


You can see that this was done by sliding the left side up. Conversely, if you slide the right side down, you take light away and put your red "in the shadows". The difference here from RGB? Your not removing or adding color, only light. Below, you can see that the red does not disappear, like it did in RGB mode. It only gets darker from the "shadow" being placed on top of it, the red is still clearly there:


This is how the "Curves Luminosity" is able to produce chrome. It takes the gray and black and maybe white blend you make with your text as in barkbark00's tutorial, and throws lights and shadows on the different areas of the span of colors, brining out the black here, making the gray more white there, etc. And usually, from the blurs and other effects you apply, the happenstance of more black here with the gray, or more white here with the black, gives you the circular or odd shapes in the chrome rather than just straight lines. In effect, the light applied by "Curves Luminosity" is "bent" or appears to as it highlights the more black area in amongst the gray or white or vise/versa.


And, playing with the position of the bar points will bring out more blacks, or more whites or grays. It's something to play around with until you achieve what you want. The key to making it chrome, or gold for that matter, is to give "Curves Luminosity" something to manipulate with your "blend" of Gaussian blurring, base color, and white and black drop shadows. Or you could even play around with the drop shadow colors as well.

This was done with a base color of yellow, and drop shadows of black and a very dark yellow, and a few tweaks in the curves settings, otherwise, following barkbark00's tutorial as written.


That is all I know about Curves for now. There is a ton more I'm sure. I learn more everyday, this is a very basic understanding of what happens when you make an adjustment. I hope it will help some of the new users to understand how "Curves" works.

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Long read, but very good information. Hopefully this will reduce the number of people who have been scared away from using the uber-power curves by its not-making-any-sense-ness. :D

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excellent read. I'm going to have to re read this several times. and refer back often until I get the basics ingrained in my noggen.

echo above comments more tuts /articles like this please.


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Wow that was a long 10 min. read....!! :D Really really good explained.... Now I understand that with RGB but still I will just draw curves and hope I'll get something good.... lol But u really wrote all nice and explained very well... Great job!!!!! Like someone said!!! We need more tutorials like this!!!! xD

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This is a great tutorial! One VERY minor thing though:



It effects the white background as it should, it removes the red and leaves us with a blue and green combo that gives us the light aqua color we see. BUT, notice that both the blue and the green are uneffected.

Those bold words should be "affects" and "unaffected," receptively. Sorry, but that just really annoys me :P

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