ExponentialTransformation (ET) is best used with images that have already been stretched using another process, so ET is best suited for non-inear images.

ET enhances contrast in darker areas without stretching noisy areas, while also preserving the highlights. By default, ET uses an internal lightness mask to protect areas of high signal.

Result of using ExponentialTransformation

Here is an image of NGC 7000, the North America nebula that has been partially processed and stretched using ArcsinhStretch:

The nebula is visible but it is faint so boosting the darker areas will improve the image.

Here’s the same image with ExponentialTransformation applied to it:

The nebula is much more visible and the darker regions are more visible, yet the background remains dark.

Using ExponentialTransformation

1. Start the process by selecting from the menu Process – IntensityTransformations – ExponentialTransformation or find it under the <All Processes> section of the Process menu.

2. Select the Function

The functions get their names based on the processes involved: SMI is the older of the two operations and may be too aggressive with some images. PIP is a newer operation and may be better suited to some images. The image shown earlier in the Result section was produced using the PIP option after first trying the SMI option.

3. Open the Real-Time preview (the open circle at the bottom-left of the ET window)

4. Slide the Order slider to the right and observe the effect on your image

5. If you’d like to have some smoothing (blurring) applied to your image, adjust the Smoothing slider

6. Once satisfied with the result, close the Real-Time preview and drag the New Instance icon (the triangle at the bottom-left of the ET window), over to your image to execute the process

Conclusion

In this article, you learned about ExponentialTransformation, when it is useful and you learned how to use ET.

More Articles In This Series

This article is part of a whole series of articles about processing images using PixInsight: