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07/18/2008 03:41:09 AM · #1
Hi everyone, could someone kindly explain to me how the Curves dialog works? I've been using levels for all my exposure needs, but can't seem to wrap my head around the concept. I feel like every time I use Curves, the image does something funny like invert itself, or turn gray in places, and it generally just pisses me off that I can't get the hang of it :(. So, If someone would kindly explain these things to me, I would like it very much. Thanks!
2678699127_2e097f4482.jpg
You can use this image to use as an example if you'd like :)

Message edited by author 2008-07-18 03:42:06.
07/18/2008 03:49:29 AM · #2
this image doesn't need any curves adjustment, seems perfect to me.
If you use the curves dialog, try the "samples" from the pulldown menu, maybe you'll understand better what it does.
07/18/2008 03:50:36 AM · #3
Being technically inept still I can't really help...I can say I like your photo though!

Also curious as to the response as I have had the same prob whenever I've attempted curves...
07/18/2008 04:00:20 AM · #4
I'm not sure what you mean about looking at the samples, I'm using CS2- should I be looking somewhere in particular for these "samples"?
07/18/2008 04:01:04 AM · #5
Originally posted by Iraklis:

Being technically inept still I can't really help...I can say I like your photo though!

Also curious as to the response as I have had the same prob whenever I've attempted curves...


Thanks!
07/18/2008 04:02:36 AM · #6
There are people on this site that are much more apt at explaining curves but I will try.
What you have in the dialog i a histogram. To understand curves you need to understand the histogram.
Each point on the diagonal line will represent a lightnes level in the picture. By manipulating the straight line and creating "curves" you increase or decrease the lightness level of that specific point and its corresponding pixels in the image.
This way you get much more control over the lightness changes you can make to an image compared to levels.
There is a good tutorial here on DPC.

EDIT: btw the image you supplied does not need any curves adjustment. It is perfect as is. Very nice.

Message edited by author 2008-07-18 04:03:30.
07/18/2008 04:10:18 AM · #7
Ok, so heres a better image to use:

2679573164_d45224be91.jpg
07/18/2008 04:22:04 AM · #8
This is as close as I could get it to what I wanted... I still wish that I could bring it out of "the fog" just a little more. And another point that I wanted to talk about is how this seems to be affecting color, you can see in the foreground rocks it turning slightly blue - a little bit more pushing on the low end and it would have turned super saturated... whats the deal?

2679585358_a15ba61500.jpg
07/18/2008 04:25:10 AM · #9
700216.jpg
Fast contrast increase with curves.
When it comes to color shifts you will have to ask someone else since I don't know enough about it to help.

Oops it got too dark while converting to web, but you get the idea.


Message edited by author 2008-07-18 04:55:33.
07/18/2008 04:49:12 AM · #10
Originally posted by Refwhett:

700216.jpg
Fast contrast increase with curves.
When it comes to color shifts you will have to ask someone else since I don't know enough about it to help.


There's actually a tutorial on removing a color cast using curves here
07/18/2008 05:13:13 AM · #11
Originally posted by scrybz:

Originally posted by Refwhett:

700216.jpg
Fast contrast increase with curves.
When it comes to color shifts you will have to ask someone else since I don't know enough about it to help.


There's actually a tutorial on removing a color cast using curves here


Ahh... well I understand it a little better, I'll still be messing around for a little while but I appreciate all your input!
07/18/2008 05:51:52 AM · #12
Originally posted by Cidpilot:

I'm not sure what you mean about looking at the samples, I'm using CS2- should I be looking somewhere in particular for these "samples"?


what I meant are the presets (pull-down menu above the graphic in the dialog box), don't remember if they have already been there with CS2 :)
07/18/2008 06:50:30 AM · #13
Color Correction

Method 1:
- New adjustment layer, Curves – view the Info palette, RGB numbers should be the same for an area that is or should be gray when it is sampled.
- CTRL+click on image places a point on the curve; Shift+CTRL+click places point on all curves (RGB)
- Info Palette – click on a gray area or area that should be gray. Write down the RGB numbers. Only want to change the color, not the brightness. These numbers need to be the same for gray but also not more than original total to retain same brightness level. Add the RGB numbers up to get the total amount of light. Divide this number by 3 to get what each output channel needs to be to achieve gray without changing brightness.
- Using the Channel pop-up, select the RGB channels individually and change the output number of each to the figure arrived at in above calculation [ (R+B+G)/3 ]
- Check image – if area is not gray that should be and steps followed correctly, check monitor calibration.

Method 2:
- New adjustment layer, curves
- Click the middle eyedropper (gamma)
- Click area that should be gray
- Area should now be gray

Method 3:
- New adjustment layer, curves
- Double click right eyedropper (white) to bring up color picker
- Set saturation (S) to 0
- Set brightness (B) to 100 then click on this number
- Use down arrow key to change number until magenta (M) and yellow (Y) readouts indicate at least 3%. Cyan will be higher, don’t worry
- Double click left eyedropper (black) and set RGB = 0. Click OK.

NOTE: Clicking OK in curves dialog box will cause PS to ask you if you would like to “save new target colors as the defaults?” If yes, PS remembers the settings and uses them every time you use the eyedroppers to color correct.

- New adjustment layer, curves
- Click black eyedropper and click on a shadow area. NOTE: Shadow area means the darkest area of the image that should contain detail.
- Click white eyedropper and click on the brightest part of the image. NOTE: Brightest area means the brightest area of the image that should contain detail.
- Click on the middle eyedropper and click on any area that should be gray in the final image. NOTE: NOT bluish or pinkish gray but pure or neutral gray. The closer to middle gray the better the correction will be.

To locate Highlight and Shadow areas:
-Image> Adjustments> Threshold
-Move slider all the way to the right then slowly move it toward the middle
-The brightest area of the image will be the first area to show up white. Area should be at least 5 or 6 pixels in size
-Once area is found, Shift+click on that area to add a color sampler to that area
NOTE: A color sampler is simply a reminder of where a specific area is in an image
-Move slider all the way to the left and then slowly back towards the center
-The darkest area of the image will be the first to show up black. Area should be at least 5 or 6 pixels in size.
-Once area is found, Shift+click on that area to add a color sampler to that area.
-Click CANCEL to get out of the Threshold dialog

NOTES:
-Clicking OK in Threshold instead of Cancel will leave the image in black and white
-Pressing cap lock while using Curves turns the cursor into a crosshair
-Choose Color Sampler tool, clear to get rid of the samplers

Tonal Adjustments, whole image

-Image> New Adjustment Layer> Curves
-Underexposed image make dark part of the curve steeper to bring out the detail
-Overexposed image make light part of the curve steeper to bring out the detail
-The steepness of the curve in any area determines how much contrast is added
-Clicking and dragging across the image will show a point on the curve relating to position of cursor in image. Place control points above and below this point and adjust that section to improve contrast/detail
-After all adjustments, check curve and image and finalize curve by adding another control point and moving so majority of curve looks normal – diagonal

-Decreasing contrast and detail – any part of the curve that is more horizontal (flatter) than the original diagonal line indicates an area where contrast has been reduced
-To make two areas the same in brightness, CTRL+click when cursor is over the area of desired brightness, note the output number then release mouse. CTRL+click on area to change and change output number to match first one
-To limit effect of curves to only brightness and not color:
Image> New Adjustment Layer> Curves…adjust
Edit> Fade Curves – luminosity mode
OR
Image> New Adjustment Layer> Curves…adjust
Mode> luminosity

If adjustments adversely change image colors, convert image to Lab Mode (Image> Mode> Lab Color) make adjustments, switch back to RGB mode.

Optimal Contrast
Window> Histogram
If used in expanded view, the histogram is 256 pixels wide – the number of shades of gray – most accurate display of image data.

If the histogram doesn’t extend the full width of the window, limited brightness. Move the upper and lower corners of the curve so the curve extends across the histogram curve. This is the same as moving the sliders underneath the gray scale to the ends of the curve.
07/18/2008 06:51:24 AM · #14
Any of the above help?
07/18/2008 08:36:02 AM · #15
Yes, all of these are helpful - especially CEJ's reply. Thanks everyone!
07/18/2008 08:55:58 AM · #16
I've noticed that (usually) as long as my curve remains a smooth curve, the tones stay normal looking. If one point of the curve is pulled abruptly too far up or down in relation to the rest of it, that's when things become unnatural looking.

BTW, I agree on your beach shot. It's wonderful and needs no more tweaking. Apparently hosted somewhere else, or I would have put it in my faves.
07/18/2008 10:19:32 AM · #17
Curves takes a while to learn. It is extremely touchy and small adjustments can make big differences. Starting with the slight s-curve will give you a general contrast boost. (to get this click three points along the line at equal intervals--slightly raise the rightmost point and slightly lower the left most)

The more practice you do you'll get more comfortable with using it to just adjust midtones, or bring down highlights, etc. I'm finally more comfortable with it after about a year of practice, however, i still don't use it on the separate color channels. good luck!
07/18/2008 10:45:33 AM · #18
I found this video tutorial to be pretty good:
//www.picturesocial.com/video/video/show?id=1483478:Video:6503

I believe I originally found it here so thanks to whoever originally posted it.
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