O.K. the curve tool is not included in psElements so for those of you that use Elements; but want to add the functionality of a curves dialog you can down load this plug in for FREE!!!

http://free.pages.at/easyfilter/smartcurve.html

(if that link does not, delete the "/smartcurve.html" and try again and select "smart curve" and the English version if you dont read German)

PhotoShop's curve tool is similar in function to the levels dialog.

it adjusts the light/dark points and the image brightness.

BUT (a big but) it is also more accurate in how it applies those light/dark/contrast adjustments.

It can also control how fast the shift from light to dark tones occurs(the image contrast)

In Levels if you move the any of the sliders, the adjustment is applied to ALL of the tones in the image.

In the Curves Dialog you can apply the adjustment to relatively specific tone areas.

let's look at the curve tool dialog.

you see the image represented as a graph.

the horizontal line controls the image input.

and the vertical line controls the image output.

the bottom left is the image dark tones and the upper right is the image light tones

when you open the dialog your image will be represented by a straight line from lower left to upper right.

this represents the how fast the image changes from light to dark. In this case it is one to one.

there is also a representation of the image's histogram, this is to help you set the white and black points.

the black and white points work exactly the same as in levels.

the gamma (gray pointer in levels) is on the line in the middle of the graph.

you can click on the line and drag it up or down(or left or right) to change the brightness of the image as a whole.

the other controls in the dialog are fairly self explanitory except the buttons that select the graph lines as 10% or 25 % increments.

If you have a group of images that you want to apply the same curve to, you can make the adustments to one and save it then apply it in a click or two

 

Here is a basic sort of group image that is nice as is but can be adjusted a bit to bring up the tones.

for a cloudy day on the beach, it is sort of contrasty. (sort of what you might get if you camera is set for a contrast boost or you use a pocket camera.)

[Note: this is a stock image that came with psCS3]

The dialog below is what you see on opening the curves tool by selecting any of image> adjustments> curves; or typing control+m or adding a curves adjustment layer from the layers pallet.

 

The image below is sort of like what you would get with a levels adjustment, but the light and dark areas are less changed.

I dragged the white and black points to the histogram then clicked the middle of the graph and pulled it left to lighten the image

When you click on the line, it installs a point for each click. each point is adjustable. Just click and drag.

what this means is, you can anchor the line at a tone you want to keep; or isolate a point you want to move without effecting the rest of the tones in the image.(very much)

For instance, say you are happy with the whites or lighter tones in an image. you can click a point at or above the center of the graph.

Then click another point along the lower third of the graph and drag it up to lighten just the shadow areas.

(the line above the first anchor point will drift down a bit in response.(it's a balance thing)

the line now looks like a shallow inverted "s"

you have now flattened the contrast curve to bring up details in the shadows. And you kept the whites from losing detail.

(I also locked in a shadow point on this)

if you went the other way, dragging the lighter point up it would steepen the contrast curve.

(and create a shallow normal "s")

These adjustments also affect the color intensity(saturation) of the image

To control this, you can use the "edit> fade" dialog and switch the merge mode to luminosity.

(or use the adjustment layer for curves in the layers pallete)

Below is an example of how the curves dialog can help with controlling a color cast though application on a per-channel basis.

(although in this case I used the gray point eyedropper on the clouds over the city, the idea is the same, optimize the curve for each color channel)

I also applied a contrast boosting "s" curve to the RGB composite(the main curve)

Below I used an "s" curve to refine the edges in a custom brush.

(I will go through some pages and put some links for further study.)

a long PDF at Luminous Landscape:

http://www.luminous-landscape.com/essays/Curves.shtml

from wikipedia:

http://en.wikipedia.org/wiki/Curve_%28tonality%29

from the Adobe Mothership:

http://www.adobe.com/designcenter/photoshop/articles/phscs2at_learncurves.html

and one that is heavier on text:

http://www.naturephotographers.net/mh0702-1.html

 

Thanks for postiing this!

Dave

I'm such a newbie that I don't actually have a good PS program yet, but I've printed this out to study for later!  Thanks!

 Thank you for this tutorial. It is a big help!

I must be a total idiot.  I've read several tutorials about curves.  I just, don't, get, it.  I need someone to come sit down with me and walk me through it.  It feels like I am reading a foreign language.

OK....

what are you missing?

the curves dialog, the levels dialog and the brightness/contrast dialog all do about the same thing.

the difference is in the fineness of control. keeping with the above sequence, that would be very fine, fine, and basic.(rough)

each of these can also be applied through the "adjustment layers" dialog under the layers pallet.

curves works on a curve graph, levels works on a bar graph,

and brightness contrast is just sliders that you push around  'til the image looks good to you.

on the curve graph, up is brighter, down is darker.

The left side is the darks, and the right side is the lights.

 you can pick any point on the curve and move it up or down.

you can set more than one point on the curve.

if you want to lighen the dark tones in the image, pick a point on the graph to the left of center and pull up.

to darken the light tones, pick a point to the right of center and pull down.

to increase the overall contrast of an image, pull up in the light tones, and down in the dark tones.

 

 

I don't know what I am missing.

Although that kindergarten-level explanation did help, a bit.

I will just have to try to work with it until I get it to do something right and I go "aha!"

ok...

how about this;

open a picture.

open the curves dialog. (control+m)

click on the diagonal line, drag it up and down.

see how the picture gets lighter and darker?

revert to the original setting (hold the alt key and click the "reset" button)

now click a point in the middle and let go, that anchors the middle tones.

now click and drag down on the lower part of the line.

let that go, and click on the upper part of the line, and drag up.

let that go and look at the line. it should look like a "lazy s" and the picture should be more contrasty.

revert again

now drag the lower part of the line up and the upper part of the line down.

the "lazy s" is now backward and the picture should have less contrast.

Wah! My mommy won't buy me cs4, blech!

Manati:

Wah! My mommy won't buy me cs4, blech!

if you have a current psCS version you can get a good discount on CS4 at the Adobe Store

if you have current version of psElements you can get a discounted upgrade to CS4 there too.

I bought CS3 for 300$ as an upgrade frome Elements 5 and I ordered CS4 extended for 300$ as a preorder upgrade.

for those that have psElements and are not going to add any version of CS, you can down load a plug-in that will add a curves dialog to Elements.

http://photoshop.pluginsworld.com/plugins/adobe/990/easy-filter/smartcurve.html

or:

http://free.pages.at/easyfilter/curves.html

 Thanx, butt I have the unedumacated version. No downloads/upgrades for me.