Maximum Entropy


MaxEnt Module Specific

The Maximum Entropy command sharpens an image while reducing noise. This command implements the Maximum Entropy De-convolution, or "MaxEnt" Method. MaxEnt works best on images having high contrast and high signal to noise ratio, as shown in this example. Note: Maximum Entropy is an optional Extension Module for Mira and is not present in the command structure unless obtained separately.

Maximum Entropy only works with luminance images. It will not work with RGB images. If you want to process an RGB image, you will need to extract the channels and process them separately. However, the dynamic range will be lower since each channel of the RGB image will have been reduced to 256 levels. For RGB images, it is best to perform Maximum Entropy processing on the luminance images before merging then into RGB form.

tip

When MaxEnt processing is active, you can break out of the loop at any time using the [Esc] key.

Choosing MaxEnt Parameters

For best results, the mathematical parameters fed to the MaxEnt algorithm need to be chosen carefully. Mira's implementation of Maximum Entropy processing reduces the parameter list to just 3 properties. Good results can be obtained for a large range of image properties using these 3 parameters: FWHM, Camera Noise, and Camera Gain. These are defined in the table below.

The Maximum Entropy dialog shows two sets of parameters:

Values in the right column are there as a guide to choosing parameters. You may choose to use those values by entering them into the left column, or use them as a reference to choose values to try.

Maximum Entropy Parameters

FWHM

The Full Width at Half Maximum (FWHM) of the point spread function for the image, measured in pixels. This measures the amount of smearing in the image. It is important not to overestimate this value or this could lead to rings around point sources and edge ripples. The value should not be less than about 2.0.

Camera Noise

For a CCD camera, this is the Readout Noise. This quantity is measured in electrons (e). For example, if the readout noise is 9.2e-, enter 9.2.

Camera Gain

The ratio of output counts to input electrons. This is a number like "2.8", meaning 2.8 electrons per count (or "ADU") in the image. Electronically, this is actually the "inverse gain" but is called the gain for a CCD camera.

Iterations

Specifies the maximum number of iterations of the de-convolution. Mira will stop early if no change is detected.

Use Cursor ROI

If checked, only the region inside the cursor is de-convolved. Otherwise, the entire image is processed.

Setting Iterations and the ROI

 Related Topics

Spatial Filter Commands, Example of Maximum Entropy Processing