Introduction: Reveal Hidden Photo Secrets With the Curves Tool

By Picture Like This
About: I'm a photographer in Austin, TX and I run a website that helps people get the most out of the photography equipment they have. Check it out at www.picturelikethis.com!

The tone curves tool is a basic photo manipulation tool that gives you complete control over how light and dark various parts of your image are. Today, I'll show you how to pull secrete images from the dark parts of pictures that you can't see. 

"Curves" as we'll call it from now on, is a very common tool, present in most photo manipulation programs. If you don't have Photoshop or Lightroom, it's ok - I actually prefer to use GIMP, a free Photoshop-like software that has TONS of capabilities. 

This Instructable is about using curves for a specific purpose - getting the details out of the shadows in a picture, but you can check out the full tutorial at my article, Curves Tool - Full Control over Tones and Contrast

Step 1: First, a Bit About Images and Sensors

Digital images are captured when a lens focuses light onto an image sensor in your camera. It's the same for all digital photography - the sensor is made up of pixels which record what color and intensity of light was hitting that sensor when you press the button to take the picture. 

Whether you're shooting with a DSLR, point & shoot, or a cell phone camera, it all happens the same. The light is recorded for a certain period of time, then the image is pushed to the memory of the camera.

If you have the capability to shoot in RAW, you have the best possible chance of getting good results because RAW files are huge files that record every bit of light without compression. But if you don't have the capability, it's ok - jpegs still capture 16.7 million colors, which is plenty to extract and image from. 

Step 2: Choose a Picture With Lots of Dark Shadows

Pick a picture you took at night, or where the subject is in front of a bright source of light, like a sunset. 

When I took this picture, it looked like 3 completely darkened silhouettes against the sky - cameras just do that sometimes, especially when you're not in full manual mode for complete control over the outcome. 

Again with the colors, JPEG images can record 16.7 million colors. This picture may look like it's just orange and black, but it's really light orange, lighter orange, even lighter orange, a bit lighter orange, and so forth. The black section is really probably about 10-100 different shades of really dark gray, red, blue, green - you name it - which is plenty. Your eyes just can't tell the difference as-is because the colors are all so close together. 

Step 3: Open the Image in Your Editor

Using photoshop, lightroom, GIMP, or another program with the curves capability, open up the image and the curves tool. 

The curves too is actually a graph of the lightness and darkness of your image. The horizontal axis (x-axis) represents all the possible colors of gray from pure black to pure white that could be in your image. If you look closely, you can even see a lightly colored histogram used as the background of the cart. I've tagged the image with the meaning of the histogram. 

The vertical axis (y-axis) represents how those parts of the image will show up when you're done. In other words, it's an input vs output graph. The black line going through the middle means the blacks look black, the grays look gray, and the whites look white. 

Step 4: Start Pulling on the Curve

Click points on the curve to add control points, and click and drag those points to manipulate the curve. Any part of the curve that you push upward will become lighter, and any part that you pull downward will become darker. 

Add one control point right in the center of the curve. This will anchor that part of the curve there so you can manipulate the left half (the shadows) without changing the right half (the highlights). 

Add another control point between the left and right halves and pull it upwards - this will cause the darker parts of the image to become lighter. 

This one took a few tries, and multiple applications of the same technique, but eventually I got it. For a full tutorial on using the tone curves tool, visit my photography tutorial website, Picture Like This, or just take this link directly to the article: 
Curves Tool - Full Control over Contrast and Tones

Step 5: Keep Learning!

For more tutorials on taking pictures, processing images, and getting the most out of the camera gear you already own, visit my  website, Picture Like This. 

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