How to Set Black and White Points Manually in Photoshop CS6
Photoshop CS6 has the kind of tools needed to make sophisticated color corrections for higher-end color printing. You can manually set black and white points if you have a problematic image. You can use the Eyedropper tools in the Levels dialog box to set the black and white points. Just follow these steps:
Open an image and choose Image→Adjustments→Levels.
Make sure you have the Info panel open (Window→Info), and display the HSB and RGB color modes. (To do this, select Panel Options from the Info panel pop-up menu and select HSB and RGB from the Color Readout pop-up menus.)
Remember that you can also apply certain adjustments, such as Levels, via an adjustment layer rather than directly to the image itself. Adjustment layers provide more editing flexibility if you later decide you need to tweak the adjustment.
Select the White Eyedropper tool and move it around the image while watching the Info panel.
Look for the lightest white in the image, which may be anywhere from 90% to 100% in brightness (the B under HSB). Select that point by clicking.
Using the Black Eyedropper tool, repeat the process outlined in Steps 2 and 3 to select the darkest black in the image, which may be anywhere from 0% to 10% in brightness (B).
The combination of these two choices redistributes the pixels from pure white to pure black.
You can also set the white and black points by moving the position of the white and black triangles on the input sliders. Or you can enter numbers in the Input Levels boxes. The three boxes represent the black, gray, and white triangles, respectively. Use the numbers 0 to 255 in the white and black boxes.
Use the Gray Eyedropper tool to remove any colorcasts. Select an area of your image that should be neutral gray, one in which the Info panel shows equal values of red, green, and blue.
The Gray Eyedropper tool isn’t available when you’re working on grayscale images.
Although you generally make changes to the entire document by using the RGB channel, you can apply changes to any one of an image’s component color channels by selecting the specific channel in the Channel pop-up menu at the top of the Levels dialog box. You can also make adjustments to selected areas only.
Adjust the output sliders at the very bottom of the Levels dialog box.
Moving the black triangle to the right reduces the contrast in the shadows and lightens the image. Moving the white triangle to the left reduces the contrast in the highlights and darkens the image.
Adjust the midtones with the gray triangle slider. (It appears between the black and white input sliders, just under the histogram.)
The values you’re adjusting are called the gamma values.
Dragging this triangle to the left lightens the midtones. Dragging it to the right darkens the midtones while leaving the highlights and shadows alone. You can also move the gray triangle by entering numbers from 9.99 to 0.1 in the center option box. The default value (1.0) lies exactly in the middle of the range.
If you’re working with a series of similar images (such as a bunch of video captures), you can save the settings to reuse them later.
You can also select a preset Levels setting, such as Increase Contrast or Lighten Shadows, from the Preset pop-up menu in the Levels dialog box. Use a preset as your starting point and then fine-tune the adjustment manually by adjusting the input sliders.
Click the Save button to store your settings.
This step saves the settings, but it doesn’t apply them. Just click the Load button to retrieve them.
Click OK to apply your settings and exit the dialog box.