Curves vs. Brightness Contrast

[aron]

I am sure by the title alone, you can realize that I have questions.

Working with digital, I find that I do a lot of brightness/contrast

adjustments; however, playing with the curves seems to brighten the

image in a cleaner fasion. I realize that these are completely

different functions, but can someone please tell me the main uses of

the curves function in Photoshop.

 

Thanks

[michael_darnton1]

Essentially, curves can do almost all color and contrast adjustments except hue/saturation/brightness. Want a little more contrast in a highlight area? Curves. More shadow detail without changing everything else? Curves. Something look a bit muddy in the midrange? Curves. Color correction to only the shadows, midrange, or highlights, or two or three? Curves.

 

The color and overall contrast and brightness stuff is pretty mundane, and easy with curves, but where it shines is in being able to tweak a small tonal area with a problem by adding some local contrast--making the skin in a face not look all one flat color, for instance, or opening up shadows, or giving highlights detail.

 

I recommended it a couple of posts down, and will say it again: Dan Margulis' "Professional Photoshop" is a great book for learning a lot of what curves can do.

[aron]

I can't wait until I can quit the day job so I can spend more time reading these type books. Not a far off goal at this point and I will take your advice.

[john_houghton]

It is usually much better to use curves rather than the brightness tool. When you adjust brightness, you add or subtract the same amount to all the pixel values. If you look at the histogram display, you will see the whole histogram shift left or right. Problems arise at the extreme ends of the histogram, which correspond to shadow and highlight detail. If you were to increase the brightness by +10, highlight detail represented by pixel values in the range 245 to 255 would be lost as all of these pixels would become the same value - 255. And this loss is irreversible. If you then reduce the brightness by -10, all those pixels will be darker at 245, but still all the same and therefore no highlight detail. With the curves tool, the adjustments will be tapered off at the ends of the range (unless you deliberately want to clip the highlights or shadows). So highlight and shadow detail is retained and the change is reversible, albeit not exactly so.

[beno_t_marchal]

<p>I went through a training session organized by Adobe recently. The instructor pointed

out that an "S" shaped curve is a more flexible alternative to the brightness/contrast

adjustment.

<p>The main reasons where (1) that you can shape the curve to bring the added contrast

exactly where you want it and (2) that, unless you explicitely clip at the end of the curve,

you will not loose any detail. The brightness/contrast clips details on both ends.

<p>He pointed out that all these controls (brightness/contrast, level, etc.) are

implemented as pre-defined curves... So curve may be less intuitive but it is the most

flexible tool.

<p>--ben<br><a href="http://www.marchal.com">marchal.com</a>

[almagnus]

Absolutely BAN Brightness/contrast... It literally clips off the edges of the histogram... in other words it is not reversible. Use levels and then curves insteas.

[bill_tuthill]

I frequently use Brightness/Contrast to adjust magic-wand-selected

areas, expecially distant forested hills that tend to wash out with

digicams more than with film. Curves seem to work better on the

entire image, but I find it's too fiddly for small areas. Watch out!

It's easy to clip colors with the Curves dialog, especially if you're

not looking at the 100% view. I saved an .ACV file that brightens

shadows and tones down highlights, which is 90% of my Curves use.