The same question about control points

[mikemeister_admin]

As I've mentioned before, it seems to me that placing a control point on a curve is just a guess....an educated guess maybe, but it's still a guess. 

If it's not a guess, then see the attached image that I posted before.  If I gave you this image printed out as a photograph.....meaning that you have no access to a computer and CM.....holding the photograph in your hand,  tell me the exact location where you'd place a control point (the x and y axis) on each RGB curve to correct anything wrong that the hue clocks are indicating.

When you have CM to use to do this, it seems as if you just place a control point somewhere, then move it along the curve to see what it does when you pull it or push it.  If it doesn't quite give you what you want, then you place other control points along the curve and move them till you get what you want.  There is no exact placement of control points....they are just guesses, right?  If not, it comes across to me that they are, because when I adjust a curve, I just grab it anywhere and move it till I get the hue clocks to read what I want them to.  I don't know an exact spot where I should grab them, I just grab them.  I know that to adjust the shadow hue clock, I need to grab the curve at the darker end of the curve.  I know that to adjust the highlight hue clock I need to adjust the light end of the curve.  And last, I know that to adjust the neutral hue clock I need to adjust the middle of the curve.  The thing is, I don't know the exact spot to place a control point, I just grab the curve in the general area and move it.

It gets really bad when I see a solution that shows curves that have numerous control points that make the curve zig-zag all over the place.  There is no way anyone can know the exact places to locate a control point on a curve like that, it's just a matter of hit or miss guessing, right?

Anyway, back to the picture I attached....can anyone name the exact location of each control point on each curve?

[ggroess]

Actually Art,
I can and hopefully you will to.  The places we choose to adjust are usually found by doing a few simple things...

For me the process is as follows:
1) Find  the shadow Point via threshold or setting a point in CM.  That is one place I want to know I have no color casts. 
2) Set a hue clock on that area or point.
3) Look to make sure the colors are all the same number "by the numbers"  if they are not I have to adjust the shadow ends of the curves to make them neutral.

4) Find the highlight point as above with threshold or point setting in CM.
5) Set another hue clock on the highlight area or point.
6) Look to make sure the colors are all the same number "by the numbers"  if they are not I have to adjust the highlight ends of the curves to make them neutral.

The next part is where it gets sort of subjective...  I look for a natural neutral something that makes sense to be neutral gray.  Sidewalks, shadows on a white shirt, anything reasonable.

I set a hue clock there and again I look for color casts.  Many times I do not correct the color cast completely out of the mid tone because I see "visually see" that the color is wrong.  That sends me looking for another place to work.  If I cannot find one I do have the option to make the best guess.....I know that defeats by the numbers correction but only for the mid tone neutral... I still fixed the shadows and highlights...

The screen shots attached show how to locate the points in question.  If you click on the grid square but not the curve line and you hover your mouse on the line without clicking you will see a set of numbers like the ones in the top left of the curve grid.  These show me the value of the curve under the mouse.  I just move up and down the curve line until I hit the number I want to adjust and click there...

Greg

[mikemeister_admin]

Okay, so once you have the hue clock set on a point....let's say the highlight, and you see that your RGB values are R=235....G=240 and B=245, then do you set all three values to the highest value of the three, that being blue since it's 245, or do you try to get them all to 255 which is pure white?

[ggroess]

Highest value being 245 so I keep the highlight details that might exist above 245 up to 255. 
I might not see them on my monitor... but they might be there and I want them if I can get them.

Greg

[mikemeister_admin]

Great post, Art!  I've had the same questions.  I know I can slide my mouse around on the image and see where the "worms" are on the curve channels, but then I guess when it comes to remembering the exact spot and go from there.  For me, the input/output numbers are confusing--I can see what they mean in terms of the place on the grid, but when I'm using my up/down arrows (which doesn't always work) to modify a point, it doesn't seem like the input/out points are related to the color number on the hue clock.  The hue clock has one number for each color--say 83 for Blue, but I can't get the i/o numbers on my curve to actually become active until I click on a point--hovering doesn't work.  Anyway, does that 83 stand for input or output on a curve?  Great help from your reply, Greg!

[ggroess]

The notation is : "Input / Output"  You cannot have an output until you make a selection. 

If you have a point selected then you will get a "number / number"  notation when you make a change.

Setting a hue clock does not select the point. 

You can set a hue clock and then right click and select "mark" to add a mark to the curve line.

Greg

[mikemeister_admin]

Rhonda, to explain what Greg just said........if you want to find the value of a color on the curve that the hue clock displays, here are some pictures that explain it.