Adobe Photoshop 7 Tutorials
Color Adjustments / Levels Effects
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Subtitles of the Movie (Adobe Photoshop 7 / Color Adjustments / Levels Effects)
Well what really happens when you run levels? I'm going to go ahead and run levels on this image, which as you can see has this bit of a color cast. So command + 'L' or control + 'L' will bring up our levels dialogue box. And I'm going to make very dramatic contrast adjustment. I'm also going to choose from the channel pull down menu and go in and adjust my channels individually. I'm going to choose to red channel, and increase the contrast specifically for the red channel, and do the same for the green channel. And go back to RGB, which will affect all of these. Make a very contrasty adjustment. And I'll say ok to that, and I'm going to run levels again. Image menu>adjustments>levels and notice what's happened to my histogram now. There are actually little slices in the image data because what Photoshop has done is it has compressed the contrast and stretched it back out of course over the 256 levels of brightness values. So in essence, what I have done is I have stretched the original brightness values, and when you do that you can see that it will actually leave these little holes. And if you do it too much, it will create a visual banding, which can be unfortunately noticeable, and probably not what you want. So I'm going to undo that, and undo that one again, and talk about some of the other options that we have for levels. One of my options is to choose auto levels, and you can see what it does is it immediately applies a level's changes and stretches out the brightness values. I'm going to go ahead and choose reset, and click on options. To talk about some of the options for the auto color enhancement. So there are basically three types of algorithms that the Photoshop levels uses. And these are also used in the other automatic color enhancements. The first one is enhance monochromatic contrast, and what this will do is it will simply affect all of the color channels in the same way. It will increase the contrast over all three of the color channels. So this will preserve any color tint or coloration your image might have. If you choose enhance per channel contrast, it will go into each individual channel and look for the bright values and dark values to increase the contrast accordingly. And when you do this, it may introduce a color hue, a color cast, or it may negate a color cast as it has done in this image which had this blue color cast. Find dark and light colors will find the average, lightest, and darkest pixels in the image and then use them to maximize the contrast. If you choose this snap neutral mid-tones, Photoshop will find the average nearly neutral color in the image and then adjust the gamma accordingly. And you can see it's a very subtle change if you enable that. And I generally prefer to enable that when I'm using an automatic type of color enhancement. The clipping values here refer to the brightest and darkest values that Photoshop will ignore before performing any kind of automatic color correction. So in this case, it won't look at the brightest white pixels, it will clip that color correction to about one half a % of the dark and light values. Sometimes this can create a too contrasting image. So if you want to, you can select the clipping values and reduce them a bit. And that looks pretty good, so I think I'm going to stick with that automatic color correction derived from my levels options.
Tutorial Information
| Course: | Adobe Photoshop 7 |
| Author: | Andrew J. Hathaway |
| SKU: | 33329 |
| ISBN: | 1889347272 |
| Release Date: | 2002-09-05 |
| Duration: | 11 hrs / 152 lessons |
| Work Files: |
Yes |
| Captions: | No |
| Compatibility: |
Vista/XP/2000, OS X, Linux QuickTime 7, Flash 8 |
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