Tài liệu Photoshop cs5 by Dayley part 12 docx

One is to simply rotate the image by a specific angle, another is to rotate the image while you are cropping it, and another is to use the Crop and Straightening utility to batch straigh

advantage is that you can do several different operations while a selection is highlighted that you cannot do while a crop is highlighted

You do not have the same cropping options available when cropping using a selection Also, even though the selection is not rectangular, the crop is Typically, the Crop tool is the best option when you are planning to crop an area of an image The ability to crop around a selection provides

an alternative option for times when you already have an area selected that fits the area that you would like to crop

Straightening an image

One of the most common editing tasks when working with images is straightening Photos taken when the camera was slightly angled, or even on its side, do not look quite right Photoshop pro-vides several different methods to straighten images that are slightly off

Photoshop provides three basic methods for straightening images One is to simply rotate the image by a specific angle, another is to rotate the image while you are cropping it, and another is to use the Crop and Straightening utility to batch straighten scanned photos

Rotating and flipping images

The easiest way to rotate an image in Photoshop is to select Image ➪ Image Rotation and then select one of the following options from the pop-up menu shown in Figure 3.14:

l 180 degrees: Rotates the image around the center axis 180 degrees.

l 90 degrees CW: Rotates the image around the center axis 90 degrees clockwise.

l 90 degrees CCW: Rotates the image around the center axis 90 degrees counter-clockwise.

l Arbitrary: Launches the Rotate Canvas dialog box that allows you to select an angle to

rotate the image as well as whether to rotate the image clockwise or counterclockwise The image size is increased to keep the full original pixels in the rotated version, and any new space that must be added is added as the background color

Note

When you rotate an image 180 degrees, the dimensions and pixels do not change When you rotate an image

90 degrees, the dimensions swap places but the pixels do not change However, when you rotate an image at

an arbitrary angle, the dimensions of the image increase to keep the corners of the rotated image More

impor-tantly, the actual pixels of the original photo are altered slightly because they are no longer aligned in the same

direction as they were Therefore, some data is lost and you may end up with some residual artifacts You

should avoid rotating images several times, because each time leads to more distortion n

l Flip Canvas Horizontal: This flips the entire canvas on its back in the horizontal

direc-tion It results in a mirrored image of the original This is similar to taking a transparent sheet and flipping it over from left to right

results in a mirrored image of the original This is similar to taking a transparent sheet and flipping it over from top to bottom

FIGURE 3.14

Using the Image Rotation menu to rotate images in Photoshop

Rotating while cropping

Another option is to rotate the image at the same time you are cropping it using the Crop tool

This has the advantage of not creating any additional background pixels to accommodate space that was not in the original image because the cropping will be rectangular

As discussed earlier, you can crop an image by selecting the Crop tool from the toolbox and then select an area in the image to crop In addition to the other options that were discussed, you can rotate the crop box by moving the mouse over the crop box until the rotation curser shown in Figure 3.15 is displayed Then click the left mouse button and drag to rotate and straighten the image

When you rotate the crop box, it rotates around the center point icon You can adjust the center point to get a better angle when rotating the crop

Tip

When using the Crop tool to straighten an image, you should turn on the grid lines in the Crop Guide Overlay

and use them to align the rotated crop box with an element of the image that should be either horizontal or

vertical, such as a water line or a building n

FIGURE 3.15

Selecting the rotation cursor around a crop box to rotate an image in Photoshop

Rotation cursor

Using the Crop and Straighten tool

One of the most common things that Photoshop is used for is retouching old photos Often these photos are scanned in batches on a flatbed scanner One of the biggest problems is that the photos move around a bit and so they are not aligned very well in the final scan Another problem is that each scanned image contains several photos when what you really want are individual photos

Photoshop provides the Crop and Straighten tool to solve both of these problems The Crop and Straighten tool analyzes the image and looks for whitespace around the images Then it copies the individual photos in the original image into new documents The results are a set of new files, each containing only a single photo that is correctly rotated

To use the Crop and Straighten tool, open the image that contains the scan of multiple photos, similar to the one in Figure 3.16 Then select File ➪ Automate ➪ Crop and Straighten Photos from the main menu in Photoshop You see a progress bar while Photoshop is analyzing the data in the image, and then some documents open containing the individual cropped and straightened photos from the original, as shown in Figure 3.16

Using the Crop and Straighten tool to automatically detect, crop, and straighten a series of photos

con-tained in a single scan

Tip

The Crop and Straighten tool can also be used even if there is only one photo in an image, as long as there is

enough of a border around the photo that Photoshop can detect the edges n

Using the Ruler tool

An excellent tool for straightening images is the Ruler tool Using the Ruler tool you can draw a line on the image and then click on the Straighten button in the options menu, shown in Figure 3.17, to straighten the image based on the angle of the ruler line The image will be straightened vertically or horizontally to match the angle of the line If the line drawn with the Ruler tool is exactly vertical or horizontal then no change is made

The Straighten option of the Ruler tool works best on images that have a reference plane such as the side of a building or a horizon that should be exactly vertical or horizontal Figure 3.17 shows

an example of using the ruler to straighten a seascape image Notice that the horizon in the original

is crooked, making the image look odd A line is drawn with the ruler tool and then when the Straighten button is clicked the horizon now matches the horizontal plane of the image

FIGURE 3.17

Using the straighten option in the Ruler tool options, you can quickly straighten an image based on the

line drawn with the Ruler tool

Straighten button Ruler line

On the Web Site

The image shown in Figure 3.17 can be found on this book’s Web site as Figure 3-17.jpg You can open it in

Photoshop and use the Ruler tool to straighten the horizon n

Trimming a border

The Trim utility provided with Photoshop allows you to quickly trim off the border around an image This can be useful tool when you are working with scans of older photos that contain bor-ders, a screen shot of an image that contains a border, or a document that has empty space around the outside

The Trim utility detects the border based on a specific color or blank pixels and then trims the edges of the document based on that color The Trim utility allows you to specify whether to use transparent pixels, the color of the pixel in the top-left corner, or the color of the pixel in the bottom-right corner of the image to trim the edges You also can specify which of the top, bottom, left, and right edges of the border are removed

To use the Trim utility to trim the border around an image, select Image ➪ Trim from the main menu to launch the Trim dialog box, shown in Figure 3.18 Then specify the options and click the

OK button to trim the image

FIGURE 3.18

Using the Trim utility to trim the border of an image

Summary

This chapter discussed the basics about image and view files Some file formats offer advantages over others depending on the purpose for which you are using them Although you likely will use the Photoshop format for most of your editing, you probably will gravitate to one of the main file types such as TIFF or JPEG for saving the edited images

Resolution and size have a relationship based on the desired output location of the images Using the Canvas Size tool, you can add additional area to an image without changing any of the existing pixels in the image

This chapter also discussed how to crop, straighten, rotate, and trim images You can use the Crop tool to crop and straighten images You also can straighten and rotate images using the options in the Rotate Image menu

In this chapter, you learned the following:

l The different file formats for images, video, and 3D objects that Photoshop is capable of supporting, what they are for, and when to use them

l Opening, resizing, and adjusting the resolution of images

l Using the Image Size tool to set the size and resolution of the image to match the destination

l Guidelines to use when cropping images

l Using the Crop and Straighten utility to detect borders, crop them, and straighten photos, all at the same time