iPhoto 5 or later Frequently Asked Questions (FAQ): Using the Adjust palette

Using the Adjust palette

1. What are Levels?

   There are normally 256 possible levels of brightness in a digital image (see Note), numbered from 0 to 255. The Levels graph, called a "histogram" (it looks like a mountain) is a visual representation of how the image data in your photo is distributed between pure black (0) and pure white (255). The left edge of the histogram represents black, while the right represents white. All other colors fall in between these two points. To simplify your experience, iPhoto uses a 0- to 100-percent scheme instead of displaying the standard 0 to 255 range.

   

   If an image's histogram doesn't touch the left point (the mountain looks like it starts a bit to the right of the left point), the image doesn't contain any pure black. You may see this with photos that are overexposed (too bright) or have poor contrast (photographers call this a "flat" image). If the histogram doesn't touch the right point, the image doesn't contain any pure white. You may see this with photos that are underexposed (too dark) or have poor contrast.

   Thankfully, you can fix less-than-stellar exposures using the Levels controls. In iPhoto, you can view an image's levels in the Adjust palette. The colors in the histogram represent the individual color channels of red, green, and blue (RGB) that make up a digital image. You can see how the colors change relative to each other when you adjust the color temperature by moving the Temperature slider, for example.

   Note: The 0 to 255 range is the mathematical limit of what's possible in an 8-bit image, like a JPEG. Eight-bit is most commonly used for actual output (like printing or web publishing). Though a much greater range is possible when working in a higher quality image (like 16-bit TIFF or RAW), the 0 to 255 point scale is generally applied as a reference in applications such as Adobe Photoshop.

    

2. How do I use Levels?

   By moving the Levels sliders in the Adjust palette, you can improve the appearance of your image. If your photo is overexposed, just move the black slider (the left one under the histogram) to the edge of where the image data starts to add black tones to your image (adjust the setting to your liking). To fix an underexposed photo, move the white (right) slider to the point where the histogram ends and adjust it to your liking. If you have an image with poor contrast, move the black and white sliders in from the opposite edges of the histogram. Do keep in mind that as you move the sliders into the image data, you sacrifice detail to gain contrast.

   As you use the other sliders (Exposure, Contrast, Brightness, and so on), watch the histogram to learn how each control affects it. Some of the adjustments can have overlapping effects, so you'll sometimes undo something you just did. There is no "wrong" way to use the adjustment tools -- just watch, learn, and stick with whatever's efficient for you.

    

3. Why isn't there a middle Levels slider?

   While other image editors have what's known as a gray (middle) slider, iPhoto only uses black and white ones in the Levels control. However, iPhoto's Exposure slider is equivalent to a middle slider (it controls the gamma, or mid-point brightness, in an image) in other applications.

   However, when you edit a RAW file, the Exposure slider acts as a true exposure adjustment. Because you can't make a retroactive change to the exposure of a non-RAW file, the Exposure slider will only adjust such an image's gamma, which is the next closest thing.

    

4. What is the difference between Brightness, Contrast, and Exposure?

   Contrast is the easiest to understand. It's the difference between the lightest and darkest tones in your image. Increasing it will give you both darker blacks and brighter whites. If the histogram (see What are Levels?) for your image does not cover the entire 0 to 100 range of levels, then you can increase the Contrast slider to "stretch" the information over a larger range. On the other hand, if the histogram of your photo is spilling off both sides (past 0 and 100), you might be able to control the image better by decreasing the Contrast slider, to bring the tones back into the visible range.

   Brightness allows you to shift the entire image toward the black or white side of the levels range without changing the contrast or any other qualities. If you watch the histogram while moving the Brightness slider, you should see it move from side to side but otherwise look unchanged in its shape. This is very useful when you already have the Contrast exactly where you want it -- just shift the image as far toward the black or white slider as you want it, then (if desired) adjust the opposite slider to finish the image.

   Exposure refers to how much light struck your camera's sensor (CCD or CMOS) when you took the photo. You obviously can't change how much light your camera captured, but you can change the way it's interpreted. RAW images have a significant advantage in adjusting Exposure, because they retain much more information. Changing the exposure on a RAW image is equivalent to retroactively changing the ISO at which the image was shot. In this sense, it is a true "exposure" adjustment. When your image is not RAW, "exposure" is a bit of a misnomer. In this case, it really just adjusts the image gamma, which is equivalent to the "gray" slider in other photo editing applications, such as Adobe Photoshop.

   Proper exposure dramatically improves an image and can eliminate the need for major brightness and contrast adjustments. If you are working with RAW images, it's a good idea to set the exposure first, then finish the image with other adjustments.

    

5. What is Saturation?

   Ever wonder why some photos have overly vibrant colors that don't seem to exist in the real world? Skies are deep blue, roses appear to bleed red, and the grass is truly greener on the other side of the pearly white fence. This color vibrancy is known as color saturation.

   iPhoto features a Saturation slider in the Adjust palette that lets you crank up the color to make your subject matter look richer and brighter. Don't like that candy-colored look? Conversely, you can use the same slider to decrease an image's saturation to get that dulled-over, ultra-urban fashion ad look.

    

6. How do I use Tint and Temperature effectively?

   The Tint and Temperature controls go hand-in-hand with the fundamental concepts for light and photography. And luckily, they're not hard to learn. To use these controls effectively, all you need to know is what impact each has on the classic lighting issues each was built to address.

   In a nutshell, the Tint slider lets you control the amount of red or green tones in your image (just like the Tint control on your TV). Move the slider to the left to add more red and lessen the amount of green. Move it toward the right to add more green and lessen the amount of red. This slider comes in handy when you're trying to make skin tones look good, want to balance out scenery that contains a lot of plants, or forgot to use your camera's fluorescent white balance setting.

   The Temperature slider is kind of like a "white balance" corrector in that it allows you to introduce more warmth (more orange tones) or coldness (more blue tones) to an image. For example, if you shot an image using the camera's Auto white balance and your prized polar bear picture is looking mighty blue, move the Temperature slider to the right to warm up the image, or you can move it left to give the image even more of an Arctic chill.

   For a longer version of this answer that contains more advanced color concepts, click here.