This chapter contains these sections:
To open Image Works, double-click the imgworks icon on the MediaTools page of the Icon Catalog.
Image Works lets you manipulate images — blur, sharpen, stretch, scale, and flip images — and save them to a file. Image Works also lets you convert color images to black and white or make photographic negatives.
The Image Works window appears in Figure 2-1.
The Image Works window contains six menus and a help menu:
| File | Lets you open, save, and print images. You can also set sampling preferences using the “Preference” menu. | |
| Edit | Contains the undo and redo commands. | |
| View | Contains commands that let you increase and decrease the size of the image. | |
| Transform | Contains commands that crop, scale, stretch, flip, or rotate an image. | |
| Enhance | Contains commands that let you use effects such as blur and sharpen, change the contrast and brightness, and change the color balance. | |
| Effects | Allows you to turn an image into black and white, apply special effects like posterize and edges, and turn an image into a photographic negative. |
The balance of the Image Works window is the image area. When you open an image, this is where it appears.
To open Image Works, choose “Media Tools” from the Find toolchest and double-click the imgworks icon.
You can open a number of different types of images in Image Works. These include:
SGI
TIFF
FIT
GIF
JFIF (JPEG compressed images)
Photo CD
To open an image in ImageWorks:
Choose “Open...” from the File menu.
Click on the name of the file you want to open.
If you're opening a Photo CD file, choose an image size by clicking one of the sizes in the “Open Photo CD As” list.
Click the Accept button.
The image appears in the Image Works window.
Some files, such as PhotoCD files, can contain multiple images in one file. You can open one of these images by using the filename:n option, where filename is the name of the file, and n is the number of the image you want to open. Use imginfo to get a list images in a file. See “Getting Information About an Image” and the imginfo man pages for more information on using imginfo
Use the “Save” command in the File menu to save your current work as is. Use “Save As...” to copy your image to a new file using a new name. The “Save As” command lets you save your image in SGI, TIFF, FIT, GIF, or JFIF format. Select the format by choosing one from the pop-up menu below “File Format.”
SGI format is used by applications on Silicon Graphics systems, including IRIS Showcase.
TIFF format is the most common and useful file format.The FIT format is not a standard, but is supported by the ImageVision Library (IL).
JFIF (JPEG compressed) format uses very little disk space at the expense of some picture detail.
GIF format is useful for online graphics presentation, such as World Wide Web documents and multimedia authoring. It does not have the color capability necessary for publishing or technical uses.
TIFF, GIF, and JFIF formats have additional options you can set. For information, see:
If you are saving an image in TIFF format, you can choose to turn compression on or off. Turning compression on significantly reduces the amount of disk space needed to store the image without reducing the quality of the image; however, if you plan to use these images in PC or Macintosh files, you will encounter fewer compatibility problems if you turn compression off.
When saving an image in GIF format, the button labeled “Set GIF Options...” below the label “GIF Options” is activated. If you click on this button, the Image Works GIF Options dialog appears. This window lets you change certain options before saving the image.
By default, Image Works uses a maximum of 64 colors when saving a file in GIF format. Dithering and interlacing are turned on. You can change these settings. You can also choose a transparency color. For more information, see:
By default, Image Works uses a maximum of 64 colors when saving a file in GIF format. You can increase or decrease the number of colors.
More colors give you a better quality image.
You may want to choose many colors to accurately represent photographs or other highly realistic images. Files containing a large number of colors take up more disk space.
Fewer colors help save disk space and network transmission time.
You may want to choose fewer colors for diagrams, line drawings, or other simple graphics.
Also, if you are creating images for the World Wide Web, remember that your content is viewable by a worldwide audience. Internet users view images using a wide range of computer systems and software, with varying color graphics capabilities. To place fewer demands on the viewer's Web browsing hardware and software, choose the fewest colors to provide acceptable quality for your images. If you place several images on one page, use fewer colors in each image to help Web browsers faithfully show all the images.
To increase or decrease the number of colors when saving to GIF format:
Click the Set GIF Options... button in the Save As... window to open the GIF Options dialog.
You can also choose “Set GIF Options...” from the File menu in Image Works to open the same dialog.
Press down on the button next to “Number of Colors to Save” and select a number from the pop-up menu.
You can choose 16, 64, 128, or 256.
Click the Accept button to make the change and close the dialog.
When using fewer colors in an image, dithering may help improve the appearance of an image. Dithering changes the pixels in an image to simulate “lost” colors. By default, Image Works uses dithering when saving to GIF format. If you are saving a simple image, like a line drawing or diagram that uses fewer colors, you may have better results if you turn dithering off.
To turn dithering off when saving to GIF format:
Click the Set GIF Options... button in the Save As... window to open the GIF Options dialog.
You can also choose “Set GIF Options...” from the File menu in Image Works to open the same dialog.
Click the box next to “Use Dithering.”
The checkmark disappears. To turn it back on, click the box. The checkmark reappears.
Click the Accept button to close the dialog.
An interlaced image displays gradually. It starts out very rough, then progresses and adds detail as it displays. If an image isn't interlaced, the image doesn't appear until the complete image is ready to display. Both processes take the same amount of time. Authors of World Wide Web pages use interlaced images to give you visual feedback instead of a blank screen while you wait for an image to display.
By default, interlacing is turned on when saving to GIF format. To turn interlacing off:
Click the Set GIF Options... button in the Save As... window to open the GIF Options dialog.
You can also choose “Set GIF Options...” from the File menu in Image Works to open the same dialog.
Click the box next to “Use Interlacing.”
The checkmark disappears. To turn it back on, click the box. The checkmark reappears.
Click the Accept button to close the dialog.
When saving images to GIF format, you can select a solid color in the image and make it transparent. This is useful when you want to eliminate the rectangular background of an image and give the impression that the image is floating on the page.
To choose a transparency color when saving images in GIF format:
Click the Set GIF Options... button in the Save As... window to open the GIF Options dialog.
You can also choose “Set GIF Options...” from the File menu in Image Works to open the same dialog.
Click the Choose Transparency Color... button.
The GIF Transparency window appears.
Select a color you want to make transparent
Move your mouse cursor across the image.
The image appears magnified in the Pixel View in the GIF Transparency window.
As the color you want to make transparent crosses behind the small square in the center of the Pixel View, click the left mouse button.
The color disappears from the image.
Click the Accept button to close the GIF Transparency window.
Click the Accept button to close the GIF Options dialog.
When saving images in JFIF format, you can adjust the compression quality of the image. By default the compression is set to high (100). At this quality, all detail is saved. Lowering the quality decreases the amount of detail and decreases the size of the file. To adjust the compression quality:
Select “JFIF” from the File Format pop-up window in the Save As... dialog box.
The slider below “JFIF Options” is activated.
Move the slider to the left to lower the quality. Move it to the right to heighten the quality.
Click the Accept button to save the file.
Choose “Set Preferences...” from the File menu to choose the resampling method for your images.
“Resampling” determines the procedure Images Works uses to stretch the image. “Nearest Neighbor” works quickly, but produces lower quality results. “Bilinear” and “Bicubic” use more complex, time-consuming methods, but produce higher quality results.
These sections tell you how to use Image Works to do many different things:
To blur an image:
Choose “Blur” from the Enhance menu.
Drag the slider to change the degree of blur, or type a percentage in the field.
Change the kernel size, if you want.
Generally, a high blur factor and large kernel size produce a very blurry image.
Click the Apply button to make your changes take effect. To return to the original image, choose “Undo” from the Edit menu.
Click Reset to reset the blur scale.
Click Close to close the blur window.
Sharpening an image makes the colors more crisp. To sharpen an image:
Choose “Sharpen” from the Enhance menu.
Drag the slider to the right to sharpen the colors in the image, or type a percentage in the field.
Change the kernel size, if you want.
Generally, a high sharpen factor and large kernel size produce a very sharp image.
Click Apply to make your changes take effect. To return to the original image, choose “Undo” from the Edit menu.
Click Reset to reset the sharpen scale.
Click Close to close the Sharpen window.
To change a color image to black and white, choose “ Color to Grayscale” from the Effects menu. To return to the original image, choose “Undo” from the Edit menu.
To turn an image into a photographic negative, choose “Negate” from the Effects menu. To return to the original image, choose “Undo” from the Edit menu.
The “Crop” command lets you cut an image, just as you would cut a picture using scissors. To crop an image:
Choose “Crop/Add Margin” from the Transform menu.
Pull down Add from the Crop button to add a margin to your image.
A selection rectangle appears in the image. Size the image using the rectangle. You can also fill in the fields with the amount you would like to crop the image, in pixels.
For example, if you enter 15 in the “pixels left” field, you snip 15 pixels off the left side of the image.
Click the Choose Color button to change the color of the crop area or margin.
Click Apply to initiate the changes. Choose “Undo” from the Edit menu to return to the original image.
Click Close to close the window.
The “Scale” command lets you resize an image and maintain the correct proportions (aspect ratio). To scale an image:
Choose “Scale” from the Transform menu.
Type the percentage by which you want to scale the image in the “Scale Factor” field or type the size (in pixels) that you want it to be.
The program figures out the percentage for you.
You can also resize by moving the handles on the corners of the image.
Click Apply to implement the changes. Choose “Undo” from the Edit menu to return to the original image.
Click Reset to reset the scale.
Click Close to close the window.
The “Stretch” command lets you resize an image without maintaining the aspect ratio. To stretch an image:
Choose “Stretch” from the Transform menu.
Type the percentage by which you want to stretch the image horizontally and vertically in the appropriate fields, or type the size (in pixels) that you want it to be.
The program figures out the percentage for you.
You can also stretch the handles on the corners of the image.
Click Apply to implement the changes. Choose “Undo” from the Edit menu to return to the original image.
Click Reset to reset the scale.
Click Close to close the window.
You can flip an image upside down or sideways using the “Flop Horizontal” and “Flip Vertical” commands in the Transform menu.
The “Rotate” command lets you rotate an image counter-clockwise at any angle. To rotate an image:
Choose “Rotate” from the Transform menu.
Type in the “Rotate Image” field the degree by which you want to rotate the image.
Click the Choose Color button to change the color of the crop area or margin.
Click Apply to initiate the changes.
Choose “Undo” from the Edit menu to return to the original image and remove any new color.
Click Close to close the window.
The Threshold feature allows you to selectively lighten and darken pixels in your image. For grayscale images, it forces all of the pixels to be either white or black. For color images, it forces all of the pixels into primary colors (black, white, red, green, blue, yellow, cyan, and magenta).
For example, in a black and white image, this means that you pick a gray level as a threshold. Everything lighter than the threshold gray becomes white. Everything darker than the threshold gray becomes black. Color images are handled just like black and white. The difference is that the threshold operation is done three times, once each for red, green, and blue.
Use Threshold on scanned line art to make edges crisper and remove background noise, or on color images for special effects.
To “threshold” an image, follow these steps:
Choose “Threshold” from the Effects menu. A dialog box appears.
To change the threshold level, drag the Threshold Level slider.
The threshold level determines how pixels are darkened and lightened in the image. Generally, pixels darker than the threshold level become black. Pixels lighter than the threshold level become white.
Click Apply to implement the changes.
Choose “Undo” from the Edit menu to return to the original image.
Click Reset to reset the scale.
Click Close to close the window.
To brighten or darken an image, follow these steps:
Choose “Brightness” from the Enhance menu. A dialog box appears.
Drag the slider bar to the left to darken the image and to the right to lighten the image.
Click Apply to implement the changes.
Choose “Undo” from the Edit menu to return to the original image.
Click Reset to reset the scale.
Click Close to close the window.
To adjust the amount of contrast in an image:
Choose “Contrast” from the Enhance menu. A dialog box appears.
To change the contrast of the dark areas:
Drag the Shadows slider to the left towards flatter to decrease the contrast, or to the right to darken the contrast.
To change the contrast of the light areas:
Drag the Highlights slider to the left towards flatter to decrease the contrast, or to the right to increase the contrast.
Click Apply to implement the changes.
Choose “Undo” from the Edit menu to return to the original image.
Click Reset to reset the scale.
Click Close to close the window.
The Posterize feature reduces the number of colors in an image. Use this feature to create special effects. To posterize an image:
Choose “Posterize” from the effects menu. A dialog box appears.
To choose the number of color levels, enter a number between 2 and 256 in the “Posterize Level” field. A smaller number produces an image with fewer colors.
Click Apply to implement the changes.
Choose “Undo” from the Edit menu to return to the original image.
Click Reset to reset the scale.
Click Close to close the window.
To adjust the balance of color in an image, follow these steps:
Choose “Color Balance” from the Enhance menu. A dialog box appears.
Balance the color.
To raise and lower the red, green, and blue, drag the appropriate sliders.
To decrease the amount of color, drag towards less.
To increase the amount of color, drag towards more.
Click Apply to implement the changes. Choose “Undo” from the Edit menu to return to the original image.
Click Reset to reset the scale.
Click Close to close the window.
A histogram graphically depicts the distribution of color in an image. Choose “Show Histogram” from the View menu. For a color image, three graphs are displayed, illustrating the red, green, and blue components of the image. For a grayscale image, one graph is displayed, illustrating the gray levels of the image.
Very dark images will have higher peaks towards the left of the histogram graph. Very light images will have higher peaks towards the right of the histogram graph.
To understand the relationship between an image and its histogram, leave it open while using the Negate, Color To Grayscale, Brightness, Contrast, Threshold, Posterize, Equalize, Color Saturation, Find Edges, and Color Balance features. Each time you change the image, the histogram automatically updates.
When you finish viewing the histogram, click the Close button to close the histogram view.
Choose “Color Saturation” from the Enhance menu. Adjust the levels in the dialog box to make the colors more or less vivid.