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Lesson 6: Using Curves in Photoshop

January 13th, 2011 · No Comments

We have many conversations at Art Shows about some of the things we do in Photoshop that help turn some of our good images into great images.  While we don’t plan to give away all our secrets, I thought it’d be a good time to get away from lessons on shooting techniques and create a lesson on using curves in Photoshop.  As always, Photographers should strive for the best image possible in the field and use only small adjustments in post-processing.  Photoshop WON’T make award-winning images out of crappy photos. 

What are curves and why use them?  Curves are what we use to adjust the entire RGB (red, green, blue) spectrum of color as well as those colors individually.  Most of the time, simple mid-tone adjustments are all that’s needed and will quickly brighten or darken your overall image.  Why not use the adjustment sliders many are probably using now?  Curves are infinitely better than using the brightness/contrast sliders because the algorithms behind curves are much more in depth and provide much more natural corrections to images.  Curves also give you control over shadows, mid-tones, and highlights individually where sliders typically affect all or nothing.  While levels are better than brightness/contrast sliders, Curves offer many more opportunities for detailed adjustments.  Explore clicking the curve line in mulitple areas to keep those areas from being adjusted along the curve.  This can be another useful way of containing shadows and highlights as well as making multiple fine adjustments all at once.

One of the first things we always do in curves is adjust the mid-tones.  While we typically use an Adjustment Layer to do this, for this lesson we won’t create any Layers (future lesson??? =).  Open a new image you want to work with.  For this lesson, I’ll work on an American Pipit image and Snowy Owl image.  Once the file is open, do the following:

1) Go to Image     2) Adjustments     3) Curves

After clicking “Curves”, the curves window will open.  I like to drag that window to an area as far off your image as possible so you can preview the changes you are applying (make sure Preview is checked!).

To make a quick mid-tone brightness correction, click and hold the line on the graph as close to the center as possible.  Slowly drag it up and to the left and you will see your image slowly get brighter.  To darken the mid-tones, simply drag the line down and to the right.  What’s great about this is it only affects mostly mid-tones.  If your image is close to clipping the highlights, it leaves those areas alone and gives a nice natural brightness adjustment to your image.

Once you’re satisfied, click OK and the curves will be applied to your image.  Below is the before and after of that mid-tone curve correction on my Pipit image.  Many are surprised to hear how simple this is and while it’s simple, it’s a very natural way of adjusting the overall brightness of your image.

For our 2nd curve adjustment we’ll work on expanding the highlights and ensure you are sending an image with a full gamma of color to be printed.  The full RGB range is from 0-255.  0 being the shadows side and 255 being the highlights side.  Generally, if you mouse around an image and notice your info showing 255/255/255, this is the quickest way to see that you have blown out highlights which is very undesirable.  On the other side of the fence, if you notice your info is showing 0/0/0 that means your shadows have no detail and you have pure blacks.  Still undesirable, just in the opposite manner.  What I like to see is a good histogram of color from about 20-240.  It’s important, however, to realize that each image is different and this range may change based on the overall tonality of each image.  This is only meant to be a starting range to work with.  Don’t be afraid to experiment!  Done correctly, this type of image will yield an amazing print because the entire range is being utilized.  When the entire range is utilized, you have a huge amount of data being sent to the printer which yields a great print.

To contain the highlights and ensure your image is curve-corrected but only to a point you set, use the highlights dropper within the curves window to ensure your highlights are extended to around 235-240 and not over.  To do this, follow the instructions above to navigate to the curves window.  Once there, DOUBLE-click on the highlights dropper.  The “Select target highlight color” window opens.  Near the bottom, set the R, G, and B values to 235/235/235 and click OK.  After that window closes, click your still-selected dropper on the whitest part of your image.  For my Snowy Owl image, this was the leading edge of the left wing. 

After you click, your curves will auto adjust so your brightest parts of the image adjust to the 235 you set earlier.  For my image, I noticed a blueish hue was introduced so I isolated the Blue channel still in the curves window and re-adjusted to get rid of that color imbalance.  In many images, I don’t have to do this extra step but it’s nice to know this can also be fixed using simple curve corrections.

Below is the before and after of the Snowy Owl image using the simple curve corrections used above.  The third image is after the fix to the blueish hue.  The final image printed extremely well.  All highlights were bright, yet contained.

 

The point of this lesson is to introduce you to the power of Curves.  While I have only touched upon the tip of the ice berg, I hope this gets you thinking and gives you a reason NOT to use brightness/contrast sliders for simple color corrections.

Let’s go over the “TOP 5″ summary points to take away from this lesson:
    
1) Strive for high quality images BEFORE post-processing
     2) Get away from sliders, use subtle curve corrections
     3) Keep your highlights contained to no more than 240/240/240
     4) R, G, and B Channels can be adjusted separately using Curves
     5) As always, have fun and share your work with us and others!

Stay close to the blog for new imagery as well as more lessons coming soon!!!

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