C13

Building Color Images: Learn how the AIP4Win color tool helps you to create stunning color images—hassle-free—from sets of red/ green/blue filtered images. For background, see Chapter 20.

Figure C.1 As you load an image, the Image Display Control appears at the upper left side of the screen. This tool never changes your image data, it controls every aspect of how your images appear on the computer screen—their size, shape, brightness, contrast, and display mode.

C.1 Basic Skills

In this tutorial you will load, display, and save images using AIP4Win. This one is the longest of all because it covers most of the basic functions of the program. You will learn these specific skills:

• How to load and display CCD images and other images using standard PC file formats,

• how to control the way an image is displayed,

• how to customize some of the features of AIP4Win,

• how to save images in FITS format, and

• how to export images using standard PC file formats.

The files for this tutorial are found in the Tutorials directory on the CD-ROM under the Using AIP4Win subdirectory.

Step 1: Starting the Program. Start AIP4Win by either clicking on the desktop icon or by running AIP4Win from the Start Menu. The program will load and display its introduction panel.

Step 2: Loading an Image. We'll begin by loading a CCD image that has been stored in the FITS format. Besides FITS, AIP4WIN supports all well-documented proprietary CCD camera formats. Click File I Open Image..., a dialog box will pop up. Use it to select your CD-ROM drive and navigate to the Basic Skills subdirectory of the Tutorials directory on the CD-ROM, select the file "m22.fts," and click Open. The file should display on the screen.

Step 3: Auto-Stretch. If the image appears all black, click the Auto button on the Image Display Control on the left side of the screen. The image should now display in a continuous range of gray tones. The auto-stretch feature automatically determines the range of gray levels best suited to display an image by examining the histogram of the image. It then stretches the image linearly to display the greatest contrast. To "unstretch" the image, click Auto Min/Max on the Display Control. The image should now appear mostly black, with only the brighter stars visible. Click Auto again and the image will reappear. By default, images are stretched when they are loaded to make them visible. The Default Display Mode buttons on the Defaults tab can turn the automatic stretching feature on and off. You can also change the default to one of the other stretch modes using these buttons. It is important to note that none of the controls on the Display Control window affect the original image, they only affect the way it is displayed on the screen.

Step 4: Display Controls. The Display Control window contains a group of controls which give you complete flexibility in how an image is displayed. The Black/White control determines the lower cutoff value, below which any pixel is displayed as black and the upper cutoff value, above which any pixel is displayed as white. Any pixels between these two values will be linearly stretched between black and white. Above these controls is a small display of the portion of the image histogram that is currently viewed. This display shows you in real time what changes you are making as you adjust the controls.

As you increase the Black control, dimmer stars and the sky background will start to disappear; and at the same time you will see the histogram stretch out off the left end of its display. As you decrease this control, faint stars, sky background and noise will start to appear. Decreasing the White control will cause brighter stars to saturate the display, burning in the center of the image. You will see the histogram stretch off the right end of its window. Increasing the White control causes the display to dim. Brightness and contrast of the image can be varied using these two controls.

The Change slider is used to adjust the sensitivity of these controls. Moving it toward the fast end makes the controls increase in large steps when the up and down arrow buttons are clicked. Moving the Change slider toward the slow end allows you to make changes in small steps.

You can also adjust the brightness and contrast using the +B, -B, +C and -C buttons. These buttons affect both the black and white values, and their sensitivity is also controlled by the setting of the Change slider.

Finally, you can type numerical values into the Black and White text boxes. When you press the enter key, the image display is updated using the values you have entered. When you have finished experimenting with the Black and White setting, click the Auto button.

Step 5: The Gamma Control. Try clicking the up and down buttons on the

Image Display Control

Current Active Image

Display I Defaults] Imager

Current Active Image

Display I Defaults] Imager

Auto

Auto Min/Max Default B/W

r Display Image as Negative

Auto

Auto Min/Max Default B/W

r Display Image as Negative

Gamma — 1.00

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