Adobe Photoshop CS4 for Photographers Tutorials
Adjustments / Levels
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Subtitles of the Movie (Adobe Photoshop CS4 for Photographers / Adjustments / Levels)
Levels Adjustments have long been the most basic and fundamental of Photoshop Exposure Adjustments. Using Levels we can set the White Point, which means how bright the brightest pixel in the image will be, and the Black Point, which determines how dark the darkest pixel will be. Together the White and Black Points control the overall contrast of the image. To set the White Point hold down the Alt or Option key and drag the right triangle to the left until you begin to see colored or white pixels appear, then back off just slightly until you don't see them. Those colored pixels represent pixels that will start to be clipped, which means they won't have detail in one or more channels. If those pixels appear white, all three channels are clipped and the pixels will appear pure white without detail. If your image has highlights that are completely blown out you won't be able to move the Slider to the left at all, and similarly you may not be able to get rid of any clipping. To set the Black Point, hold down the Alt or Option key and drag the left Slider to the right until colored or black pixels appear. Those are pixels that will have clipping in one or more channels in the shadows, which means they'll be lacking detail. Back off just slightly from that point. You can have Photoshop automatically reveal Clipping whenever you adjust the triangles by going to the fly-out menu and toggling on the Show Clipping for Black-White Points. In some images, such as this image, I can't move the right triangle at all, as you can see there's already clipping showing, which is in the cloud area, and similarly I can't mov the black triangle at all to set the Black Point because there's clipping in the shadow areas in the trees. This image is more contrasty to begin with and so I don't need to move the White and Black Points to increase the contrast. Let's go back to the other image. After setting the White Points you want to check the image visually because not every image should use the entire Tonal Range. Some images, such as moody, faulty images will only use a portion of them. Similarly you may want some clipping in some images such as when there are specular highlights, bright, white areas that we expect to be pure white, such as sun reflecting off water or metal, and sometimes some small shadow areas that you might want to be pure black to add depth and dimension. To do this you'll need to show clipping for Black and White Points off and then just visually adjust the White and Black Point Sliders. The middle triangle is used to control the overall brightness of the image. Moving it left makes it brighter and to the right makes the image a little darker. Down here in the box we can see the values and any changes that we've made on these three Sliders. The Output Slider determines the range of tonalities to use when you output your image. If you find that your prints tend to have shadow areas that are too dark you may want to move the Black Point over slightly to be within about 10 to 15. I'm going to leave it at 11. Similarly, if you want to make sure that even the brightest pixels in the image have some ink laid down on the paper you may want to reduce the right end of the Slider to about 248, or 249. Pixels with values of 255 in all three channels usually show as just the paper so if the paper isn't pure white they can look off. And if you look at the print from an angle, seeing a lack of ink may also look odd. However, setting the Output Levels is not as necessary with today's printers as it used to be. You can click on this Icon to update the histogram that's used in the Levels dialog. When you see that warning it means that it hasn't been updated following your last changes. You can use the Eyedroppers to remove color casts, which we'll look at in the movie on removing color casts. You could also work individually with the red, green, or blue channels to alter the color cast within the image, but in most cases it's easier to use one of the Color Adjustments, such as Color Balance or Selective Color, so we leave this on the RGB Channel. In the Levels drop-down there are a series of Preset values that you could try, but generally it's better to set the Sliders individually for your image, and it's very easy and fast to do. Since the arrival of Camera Raw many people use it to determine the White and Black Points for the image as well as the image Brightness. Nonetheless, knowing how to use Levels enables you to perform those adjustments within Photoshop if you decide that the image Contrast or Brightness needs to be modified after you've left the Camera Raw interface, or if you want to perform those adjustments on a Layer Mask. There are also some advanced techniques making selections from a channel where you need to make a Levels adjustment on a channel before turning it into a selection.
Tutorial Information
| Course: | Adobe Photoshop CS4 for Photographers |
| Author: | Ellen Anon |
| SKU: | 34036 |
| ISBN: | 1-935320-74-2 |
| Release Date: | 2009-09-23 |
| Duration: | 8.5 hrs / 112 lessons |
| Work Files: |
Yes |
| Captions: | No |
| Compatibility: |
Vista/XP/2000, OS X, Linux QuickTime 7, Flash 8 |
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