3-2 : Correcting Image Exposure
In tutorial 3-1, I explained the basics of exposure as well as some theory. This tutorial will show you how to correct an image that is either too bright or too dark. There are a few ways of doing this in Photoshop, and the method you use will depend on a few things like how much correction is needed, how much time you want to spend and your ability. Try each method and see how you like it. You might find that initially you keep with the simpler methods, but as time goes on you will find a use for each.
Unlike the first level of tutorials when you learned about the toolbar, this level will use a drop menu. Find the menu shown below - you'll be using it a lot. I will use the notation of "Image > Adjustments > sample" to guide you to the tool. That means that you look for the Image menu at the top of the screen, click it, then look for Adjustments in that menu, and navigate to the required tool. There is a video at the bottom of the page to show more about these concepts.
Tip: When working your own photos or these samples images, you can make a duplicate for practicing on. Just navigate to Image > Duplicate and a copy will open up and your changes won't affect your original. In this tutorial you can also make a duplicate layer of the original image before each technique. This way, you can compare the different results. Also, you can create a duplicate layer to check your new version against the original.
Below is a photo of some Sandhill Cranes taken during their migration stop in Nebraska. I had very little light to work with in the morning, and this is a typical shot of what I ended up with.
Yes, you can see the birds, but I won't selling this one to National Geographic, it's way too dull.
Download the image here to use in the tutorial. Or right-click the image above and 'Copy and Paste it into Photoshop" by starting a new file after copying the image and then type CTRL+V. Or use one of your own images.
The first thing to consider is that if you can automate a process, it will be fast and easy - but not necessarily give you the best result. Auto Levels is a function in Photoshop that will determine what it thinks is the best exposure and correct the image with the press of a button. It will usually do a good job, but I find that it can sometimes produce a slight color shift as well and not give me the best result. Auto Levels is a good tool to use when you don't know what to do with an image. When you're starting out, you might think that your image is great, but if you use the Auto Levels method, you'll sometimes find that the image can be improved. Occasionally, you'll know that the image is off, but you don't know how to proceed. Auto Levels can sometimes get you on the right path.
Under exposed images like this can fixed quickly by using Auto Levels. Older versions of Photoshop will have "Auto Levels" in the main section of the Image menu. For CS4, you need to go to the Image > Adjustment > Levels and you will see this window appear.
Ignore the rest of the window for now (you'll look at it soon).You'll see that Photoshop will do it's best to correct it and give you an example like the right side of the image below.
That's really all there is to Auto Levels. If you have some digital images on your computer, open them up and see what effect the Auto Levels tool has on them. If you don't have any images, you can do a google search for badly exposed images and use some of them to practice on.
Brightness & Contrast
Brightness is the next simplest way of adjusting exposure in an image. It gives you control over how much brighter or darker you want the image to be, rather than just leaving it to Photoshop. With the badly exposed image open, navigate to this menu item: Image > Adjustments > Brightness/Contrast. You will see two sliders that allow you to individually control the Brightness (top) and Contrast (bottom). Move the Brightness slider to the right and left to see how it changes the photo. Move it to the position that you feel is the best result is. Then you can optionally adjust the contrast slider to make further changes.
Below is the crane image adjusted using Brightness and Contrast (I selected half to show the difference):
You'll notice that I have made mine a little darker than Photoshop did using Auto Levels. In this case, I thought that the water was a little washed out previously. I lightened the image as much as I could without making the water too bright. It's a fine line, but at least now the detail in the birds is still visible and the water isn't too bright.
Once again, open some poorly exposed images and try to correct them with Brightness and Contrast. You'll see that this method is also quick and easy while just requiring a steady hand to move the slider in small increments (or you can type in the value) and a good eye for what you like in a photo- "No experience necessary."
You have already tried Auto Levels, so now it's your turn to try setting Levels yourself. Adjusting an image's exposure levels gives you a lot of control of light, dark and midrange areas. This is probably the most common way of adjusting an image.
Have a look at the image below - it shows the corrected area, as well as the Levels dialog box.
What you'll first see is an outline of the Loch Ness Monster. That shape is actually called a Histogram and it graphically displays the exposure range in your image (or selected area). Below the Histogram are 3 sliders. The black one on the left is the shadows slider. The center one is for midtones, and the white slider is used to control highlights. How you adjust these is entirely up to the user, but here are some quick points.
Move the black (shadows) slider to where the bottom left of the histogram reaches the lowest point.
Move the white (highlights) slider to the left where the bottom right of the histogram reaches the lowest point.
Slide the gray (midtones) slider to the place where it most favorably adjusts the medium tones of the image.
This method will work on most photos. The black slider allows you to shorten the histogram to the point where the darkest area ( bottom left) will become black in the image. This is desirable, unless you know the darkest area is not actually black. Moving the highlight slider to the left allows you to make the lightest area white (depending upon color cast). The middle slider is needed to create a fine touch on the midtones. Slide it back and forth to see its effects.
If you compare the image adjusted with Levels against the others, you'll notice that it has more contrast and 'depth'. Adjusting Levels varies from image to image. Some will have more dark areas, some will have more light areas. Using the simple steps above will work on a vast majority of images.
Adjusting with Curves gives you the most control over an image. Curves allow you to create a smooth... well - curve that determines the adjustment. This gives you a cleaner tonal range (the range between white and black). Below is the image adjusted using Curves.
You'll notice that I have a high contrast image with stronger colors, I feel that it shows the birds off against the water. Once again, your results may vary.
To start the Curves dialog box, Navigate to the menu item by pressing Image > Adjustments > Curves or press CTRL+M and you will see the something like the image below.
Your image won't have the 3 small boxes in the histogram. I have added them to show you how I start when using Curves. These boxes allow me to control the curve with 3 different grips. I use one for the shadows, one for the highlights and one for the midtones. Many images will be improved by creating what is called an "S-Curve". Below is the S-Curve I used for the Crane image.
In this example, I took the darker areas (left side) and dropped them down - this gives me fuller dark tones. I took the light areas and raised them up - this lightens the highlights. I also moved the bottom highlight slider to left. Then the Midtones are adjusted to finish the correction (make sure to check the Preview box under options, to see what changes you are making to the image.).
A lot of images can be improved by using the Shadow/Highlight tool. With this tool, you can have control over the range of tone in an image. Specifically, you can control the highlights (bright areas) independently from the shadows (dark areas). To use this tool, navigate to Image > Adjustments > Shadow/Highlight and you will see this dialog box.
By default, the Shadows > Amount slider will move to 50 - in this example (since it's already dark), you can move it the left to make the shadows darker.. You want to adjust the Highlights > Amount slider to the right and darken the highlights. Then give the Adjustment > Midtone Contrast a little boost to the right if needed.
For each area you can select the Amount (how much effect), the Tonal Width (how much variance between light and dark) and Radius (area around each pixel that is used to determine if the pixel is in shadows or highlights). Color Correction and Midtone Contrast are self explanatory. Black Clip can be set higher to remove detail in the shadows and White Clip can be set higher to remove details in the highlights.
When you first apply this tool, Photoshop will set some default values. Use these as a starting point to get the image you want. You can set them in any order, but try different combinations before settling on a final image - you'll be surprised how much you can change your image. Below is the Crane image after being adjusted with this tool.
There is nothing wrong with adjusting using Curves, then fine tuning again with Levels - or vice versa. You can also use the Auto Levels then adjust the image with Curves. If you are new to exposure, try lots of variations. Use the Preview button - a lot. If you make a mistake, just undo the last change (Ctrl+Z).
Below is a final version. I have combined the methods above and used a couple of other corrections that will be shown in later tutorials.
Setting Exposure with Pickers
A final quick and easy way to correct photos is to use the color pickers in the Levels tool. This allows you select and area in the image that you want to have black, another area you want white, and other you want gray. Look at the image below - it's an underexposed photo of a flower. You'll see two targets that will guide you to areas to pick for white and black points.
This image works because there are distinct areas that I can consider black and white. Open the Levels dialog and look for the eyedroppers. You'll see three - black, gray and white.
Pick the white eyedropper and select the brightest area in the white part of the flower. Take the black eyedropper and select the darkest area in the background. The gray eyedropper won't be used here, but it is great for color correction (later tutorial). Below is the image that has been corrected just by selecting these two points.
I could have saved a lot time if I had just exposed the photo properly in the first place. In one case (the cranes), I was limited by light as the sun had just risen. Not every image you take will be perfectly exposed to your liking. That's where corrections in exposure come in. I highly recommend that you learn the various methods shown here as you'll be able save some mediocre images by making them great with a little effort. Start with the simpler methods and learn what makes a good exposure.
Search google for Overexposed images to correct.
Search google for Underexposed images to correct.