Tự học Photoshop

Image correction made easy with the Levels command


Does your photo look dull, lacking contrast? Or, does it have a color cast? Is it reddish or greenish? Adobe Photoshop`s Levels command lets you correct the tonal range and color balance of an image by adjusting intensity levels of the image`s shadows, midtones, and highlights. In this tutorial, you`ll learn how to adjust the tonality and color in your images using the Levels command.


1. Open an Image in Photoshop.
Choose File > Open or double-click a thumbnail in the File Browser. Before you start making adjustments, evaluate the image tonality. Is it too light or dark? Does it have too much or too little contrast? Is there a color cast?


2. Create a new Levels adjustment layer.
Choose Layer > New Adjustment Layer > Levels, and then click OK in the New Layer dialog box. You can also open the Levels command by choosing Image > Adjustments > Levels. However, with an adjustment layer, you are applying the tonal correction on a separate layer. The original image is untouched. If you decide you don`t like your changes, you can change them at any time or simply discard the adjustment layer and return to your original image.
A useful tool for evaluating an image`s tonality is the histogram displayed in the Levels dialog box. A histogram illustrates how pixels in an image are distributed by graphing the number of pixels at each color intensity level. This can show you whether the image contains enough detail in the shadows (shown in the left part of the histogram), midtones (shown in the middle), and highlights (shown in the right part) to create good overall contrast in the image.


3. Set the shadows and highlights.
Move the Black Point Input slider and the White Point Input slider (located directly beneath the histogram) inward from the edges of the histogram. Moving the Black Point Input slider maps all image values at its position or below to the Output Levels black point (set by default to 0, or pure black). Moving the White Point Input slider maps image values at its position or above to the Output Levels white point (set by default to 255, or pure white).
For example, if your image is too dark, try moving the Input White Point slider to the left. This maps more values in the image to 255 (the Output Levels white point), making them lighter.


4. Adjust the midtones.
Move the middle Input slider to the left to lighten the image or to the right to darken the image.
The middle Input slider adjusts the gamma in the image. It moves the midtone (level 128) and changes the intensity values of the middle range of gray tones without dramatically altering the highlights and shadows.


5. Remove the color cast.
Select the Set Gray Point Eyedropper tool in the Levels dialog box. Click an area in the image that contains only a gray tone, or an area containing as few colors as possible. It`s easier to color balance an image by first identifying an area that should be neutral and then removing the color cast from that area. With such a correction, all other colors in the image should be color balanced, too. The eyedropper tools work best on an image with easily identified neutrals.
Advanced users often use the Levels command to adjust individual channels and remove a color cast. Choose a channel from the Channel menu of the Levels dialog box and then adjust the Input sliders.


Remove red-eye in images


There`s nothing more frustrating than having a great picture ruined when a person`s eyes come out bright red. Adobe Photoshop gives you a simple way to fix red-eye using the Color Replacement tool. In this tutorial, you`ll learn how to use the tool to fix red-eye in just a few steps.


1. Open your image.
Open the image that you want to repair. Try zooming in so you can easily see the red eyes that need to be fixed. Then, select the Color Replacement tool (located in the toolbox with the Healing Brush and Patch tool).


2. Choose a brush tip.
Choose a brush tip from the options bar. The brush tip should be smaller than the red area of the eye to make correcting the red-eye easier.


3. Set options for the Color Replacement tool.
In the options bar, you can choose settings that help you fix red-eye. For Mode, make sure that Color is selected. For the Sampling option, choose Once to erase only areas containing the color that you target. For the Limits option, select Discontiguous to replace the sampled color wherever it occurs under the brush. Drag the Tolerance slider to a low value (around 30 percent) to replace only the few colors very similar to the pixels you click.
4. Choose a color to replace the red.
Typically, black is a good choice, but you could try other colors to more closely resemble a person`s eye