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February 2003

Digging Through The Levels

One of the things that many people want to do with their photos is to adjust the tonality, the relative lightness or darkness of an image. You often get a great shot that is too dark or has a distracting ‘hot spot.’ There are several ways to adjust the tonality of your images in the full version of Adobe Photoshop: Curves, Brightness/Contrast, Hue/Saturation, and Levels. Some of these are very useful for the experienced Photoshop user, but Adobe wisely removed the more advanced ones from Photoshop Elements since it is targeted at the home/amateur Photoshopper. This month, I’m taking a look at Levels. It is a great tool, and while not as flexible as Curves, it is easier to use and understand and it is included in Photoshop Elements.

Fig. 1

The Levels dialog box shows a Histogram of your image (Fig 1). A Histogram (from the Greek word histos meaning web, beam or mast) is a graphical representation that shows the frequency distribution of tones in the image using a series of contiguous vertical bars. The higher the bar, the more pixels of that tone there are in the image. In the full version of Photoshop you can even call up the Histogram by itself (select Histogram from the Image menu) to see a bunch of statistics for your image). Gaps in the Histogram don’t necessarily indicate a problem with the image unless there are large gaps with low pixel counts.

Basically, the Levels dialog is divided into two sections: Input Levels and Output Levels. The Input Levels is where you see the Histogram with three triangles beneath it, one black, one gray and one white. These are sliders that you can use to adjust your image. By moving the white slider to the left you will make the image lighter, move the black triangle to the right to make the image darker. What this does is tell Photoshop to make any value right of the white slider to be white and any value left of the black slider to be black. By holding down a modifier key (Alt on Windows, Option on MacOS) while you are moving these sliders you will see the parts of the image that will be most affected.

When you do this, you will essentially be throwing away the highlight or shadow detail past the slider. If your image has little or no data there, then you haven’t lost anything. It is a good practice to adjust the sliders to the first group of Histogram bars that you can see. This sets the darkest and lightest values to black and white correspondingly and increases the tonality of the image proportionately and can dramatically alter you highlights and shadows.

Fig. 2

Figure 2 shows a typical digital camera image. Notice how the only white in the image is where the flash flared off of the reflective material of the jacket on the right. This part of the image reflected more of the light of the flash to the camera causing the rest of the image to be underexposed. This is represented on the Histogram by the slight amount of bars on the far right and a large gap before the next set of values. By moving the white-point triangle to the next area on the Histogram we get more realistic tonal balance, although the image is still a little dark overall (Fig 3).

Fig. 3

This of course assumes that you have an image that should have a White and Black Point. A photo of a sunset may not have any black in it, but that is the exception. Most images will benefit from this. Using the corresponding eyedroppers below the buttons, you can manually select a Black Point and White Point. With the grey eyedropper you can select an area in your image that should be neutral to remove a color cast and color correct your photograph.

The gray Input Level slider adjusts the midtones of an image. This middle slider will make an image overall darker when moved to the right and lighter when positioned to the left. This is a great way to adjust an image without changing the black and white values. In the sample image, I can lighten it up by moving the gray slider to the left (Fig 4).

Fig. 4

The bottom part of the Levels dialog, the Output Levels, works in a similar manner as the top, but gives you a different result and is a great way to stylize and image. By moving the black output slider you change the shadow value, making the image lighter the farther you move it to the right. Moving the white triangle has the opposite effect. This is a very easy way to get a ghosted image effect (Fig 5).

Fig. 5

Since the Levels adjusts the black and white level of an image, and color images are usually made up of three grayscale Channels (Red-Green-Blue or RGB), you can use Levels to adjust the color of an image. Using the pop-up menu at the top, you can select one of the individual Channels to view and manipulate its Histogram.

Clicking the Auto button (or selecting Auto Levels from the menu) will set the darkest value in your image to black and the lightest value to white. This will often do a decent job on your image, but don’t rely on it exclusively.

Levels is a very powerful tool in the quest to make your images the best they can be. Fortunately, the gurus at Adobe had the good sense to leave it in Photoshop Elements. It is an excellent, convenient place where you can correct tone, color and contrast as well as create a cool effect.

Paul Vaughn is a freelance graphic artist, writer and web designer. If you would like to see the Graphics Guy address a specific topic email Paul Vaughn at Mr. Vaughn digs the Levels, but is a Curves snob.


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