controls, used to set the black and white pixel values in the image. The Low and High Pixel Values controls are automatically updated by clicking the Auto button after adjusting the Black Point and White Point controls. They can also be set manually,
• a Transfer tab, which contains buttons to set the Scaling Type and its associated parameters. This controls the shape of the transfer function,
• an Outputs tab, which contains the Low Output PV and High Output PV controls, used to set the output range of the pixel values in the image,
• an Options tab, which contains controls that allow you to adjust what information is displayed in this tool,
• a Preview display, allowing you to see the results of a scaling operation before it is performed on the whole image. This is updated by clicking the Preview button, or by changing any of the parameters on this tool.
Step 3: Set the Scaling Range. Initially, the Min PV and Max PV values are set to the values determined by the default settings of the Black Point and White Point controls. Leaving the Scaling type set at Linear for now, set the Black Point to 0.01 and the White Point to 0.98, and then click the Auto button. You will see that Low/High Pixel Values change to near 51 and 172. If the preview display hasn't updated yet, click the Preview button to see what the image will look like with these values. Suddenly, the familiar form of the Eagle Nebula appears in the preview display. The preview capability operates on a reduced-size version of the CCD image. (It may not display the entire image.) It is much faster than trying out different combinations of Low/High Pixel Values, and Scaling Types and generat ing a new image for each one. This is especially important if you have limited memory, a slower CPU, or a large image loaded.
Step 4: Create a Scaled Image. Click the Apply button and a new image will be created from the original, scaled using the parameters you entered. Click on the Info window to bring it to the foreground and click its Update button; you will see that the Min PV is now zero, the Max PV is 65535. Examine the two images side by side and notice how much more detail is visible.
Step 5: Gamma Scaling. Click on the original "ml6.fts" image to make it current. Set the Black Point and White Point values to 0.01 and 0.98 and select Gamma scaling on the Transfer tab. Click on the buttons to the right of the Gamma control in the Scaling Parameters box to obtain a value of 1.8. Notice that as the value increases from its default of zero, the low-level detail is now more prominent. Click the Apply button to create a new image and compare it to the one created using linear scaling. Notice the difference in the small histogram displayed on the Image Display Control as you click on the titlebar of the linear scaled image and then the titlebar of the gamma scaled image. See how the lower values in the histogram have been spread out.
Step 6: Gammalog Scaling. Perform the previous step again, but this time select Gammalog scaling. Remember to re-select the "ml6.fts" image to make it the current image. Use the default GammaLog value of 0.350. Compare the image you created to the Gamma scaled image. Notice how the low-level detail is enhanced, but the background contrast has increased.
Step 7: Sawtooth Scaling. Select Sawtooth scaling. Use the default value for Sawteeth of 5. Remember to select the original image and to reset the Low Point and High Point values to 0.01 and 0.98 and to click the Auto button. The Preview display will show you a grayscale that repeats itself over and over to show up a great deal of detail in the structure of this nebula. This type of scaling is not always very pretty, but it is hard to beat when you want to see the subtle details.
Step 8: Experiment. Try out the different scaling techniques and play with the parameters to get a feel for how the tool affects different images.
Close all the open images and tools when you are finished. You can do this in one step by clicking on the Window\Close all Images menu item.
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