Color gamuts in Photoshop

A gamut is the range of colors that a color system can display or print. The spectrum of colors seen by the human eye is wider than the gamut available in any color model.

Among the color models used in Photoshop, L*a*b has the largest gamut, encompassing all colors in the RGB and CMYK gamuts. Typically, RGB gamuts contain the subset of these colors that can be viewed on a computer or television monitor (which emits red, green, and blue light). Therefore, some colors, such as pure cyan or pure yellow, can't be displayed accurately on a monitor.

CMYK gamuts are smaller, consisting only of colors that can be printed using process-color inks. When colors that cannot be printed are displayed on-screen, they are referred to as out-of-gamut colors--that is, outside a CMYK gamut.

Important: The gamut for an RGB or CMYK image depends on its document profile.

Color gamuts: A. A Lab color gamut B. An RGB color gamut C. A CMYK color gamut.

About color modes and models in Photoshop

A color mode determines the color model used to display and print images. Photoshop bases its color modes on established models for describing and reproducing color. Common models include HSB (hue, saturation, brightness); RGB (red, green, blue); CMYK (cyan, magenta, yellow, black); and CIE L*a*b*. Photoshop also includes modes for specialized color output such as Indexed Color and Duotone. ImageReady uses RGB mode to work with images.

In addition to determining the number of colors that can be displayed in an image, color modes affect the number of channels and the file size of an image.

 You can set up the Info palette so that you can select any tool, position the pointer over any part of an image, and determine the color value under the pointer. You can customize the Info palette and color samplers to express color values using HSB, RGB, CMYK, Lab, or Grayscale modes without changing the mode of the image itself.and the procedure to change Info palette options in Using the Info palette (Photoshop).

Transforming perspective while cropping in Photoshop

The crop tool in Photoshop has an additional option that allows you to transform the perspective in an image. This is very useful when working with images that contain keystone distortion. Keystone distortion occurs when an object is photographed from an angle rather than from a straight-on view. For example, if you take a picture of a a tall building from ground level, the edges of the building appear closer at the top than they do at the bottom.

Note: You cannot transform the perspective of 16-bit-per-channel images.

 Steps to transform perspective: A. Draw initial cropping marquee B. Adjust cropping marquee to match the object's edges C. Extend the cropping bounds D. Final image

To transform the perspective in an image:

1. Select the crop tool and set the crop mode.
2. Drag the cropping marquee around an object that was rectangular in the original scene (although it doesn't appear rectangular in the image). You'll use the edges of this object to define the perspective in the image. The marquee doesn't have to be precise--you'll adjust it later.
Important: You must select an object that was rectangular in the original scene or Photoshop will not be able to transform the perspective in the image.
3. Select Perspective in the options bar, and set the other options as desired.
   
4. Move the corner handles of the cropping marquee to match the object's edges. This defines the perspective in the image, so it is important to precisely match the object's edges.
5. Drag the side handles to extend the cropping bounds while preserving the perspective.
Important: Do not move the center point of the cropping marquee. Photoshop needs to know the original center point of the image in order to perform perspective correction.
6. Do one of the following:
• Press Enter (Windows) or Return (Mac OS); click the Commit button in the options bar; or double-click inside the cropping marquee.
• To cancel the cropping operation, press Esc or click the Cancel button in the options bar.

If Photoshop displays an error, it is probably due to improper placement of the corner handles or center point. Click Cancel to go back and adjust the cropping marquee; click Don't Crop to cancel the cropping operation. An error may also occur if you're working with a previously cropped image.

How To Changing the size of the work canvas

The Canvas Size command lets you add or remove work space around an existing image. You can crop an image by decreasing the canvas area. Added canvas appears in the same color or transparency as the background.

To use the Canvas Size command:

1. Choose Image > Canvas Size.
2. (Photoshop) Choose the units of measurement you want.
3. The Columns option measures width in terms of the columns specified in the Rulers & Units preferences.

4. Do one of the following:
• Enter the dimensions you want the canvas to be in the Width and Height boxes.
• Select Relative, and enter the amount by which you want to increase or decrease the size of the canvas. (Enter a negative number to decrease the size of the canvas.)
5. For Anchor, click a square to indicate where to position the existing image on the new canvas.
6. Click OK.

Original canvas, and canvas added to top of image

How To Making Color Adjustments In Photoshop

There are two ways to adjust the colors in an image. The first method is to choose a command from the Image > Adjustments submenu. This method permanently alters the pixels in the active layer.

The second method is to use an adjustment layer. Adjustment layers let you experiment with color and tonal adjustments without permanently modifying the pixels in the image. The color and tonal changes reside within the adjustment layer, which acts as a veil through which the underlying image layers appear. You must use Photoshop to create and edit adjustment layers; however, you can view existing adjustment layers in ImageReady. 

To open a color adjustment dialog box:

1. If you want to make adjustments to just a portion of your image, select that portion. If you make no selection, the adjustment will be applied to the entire image.

2. Do one of the following:

·         Choose Image > Adjustments, and choose a command from the submenu.

·         (Photoshop) Create an adjustment layer.

·         (Photoshop) Double-click the thumbnail of an existing adjustment layer in the Layers palette.

To see your adjustments in the image before accepting them, select Preview in the color adjustment dialog box. 

### To cancel changes without closing a color adjustment dialog box, hold down Alt (Windows) or Option (Mac OS) to change the Cancel button to Reset; then click Reset. This resets the dialog box to the values it had prior to your changes.

How to Using the art history brush tool in Photoshop

The art history brush tool lets you paint with stylized strokes, using the source data from a specified history state or snapshot. By experimenting with different paint style, size, and tolerance options, you can simulate the texture of painting with different colors and artistic styles.

Like the history brush, the art history brush uses a specified history state or snapshot as the source data. The history brush, however, paints by recreating the specified source data, while the art history brush uses that data along with the options you set to create different colors and artistic styles.

For a variety of visual effects, experiment with applying filters or filling an image with a solid color before painting with the art history brush tool. Also try increasing the size of the image by a factor of 4 to soften the details.

Example of using the art history brush tool: A. Original B. White fill C. Large brush D. Small brush To use the art history brush tool:

1. In the History palette, click the left column of the state or snapshot to use as the source for the art history brush tool. A brush icon appears next to the source history state.

2. Select the art history brush tool .

3. Do the following in the options bar:

·         Choose a brush and set brush options. (See Working with brushes.)

·         Specify a blending mode and opacity for the paint. (See Setting options for painting and editing tools.)

·         Choose an option from the Style menu to control the shape of the paint stroke.

·         For Area, enter a value to specify the area covered by the paint strokes. The greater the size, the larger the covered area and more numerous the strokes.

·         For Tolerance, enter a value or drag the slider to limit the regions where paint strokes can be applied. A low tolerance lets you paint unlimited strokes anywhere in the image. A high tolerance limits paint strokes to areas that differ considerably from the color in the source state or snapshot.

Drag in the image to paint.