Differential Contrast Enhancement

Use the Process > Enhancements > Differential Contrast Enhancement filter to enhance image contrast.

The DCE-filter (Differential Contrast Enhancement) enhances weak contrast differences selectively. This means that image structures that are barely distinguishable from one another in the original image will become visible in the resulting image. Resulting images become more detailed and appear more focused.

The dialog box that is opened when you use an image processing operation is made up in the same way for every operation. Click here to switch to a description of this dialog box.

Parameters for the DCE filter

What is differential contrast?

Most images are comprised of greater and lesser intensity modulations. Greater intensity modulations are significant, clearly-visible intensity value differences. Lesser intensity value modulations are minimal, barely-visible intensity value differences. The low intensity value modulations are what define differential contrast. The DCE-filter separates the two image components in order to selectively enhance the lesser intensity value modulations.

Bandwidth

The Bandwidth parameter defines the range of gray values belonging to the lesser intensity modulations. The bandwidth accepts values between 0 and 100. When the bandwidth is narrow, intensity modulations of a minimal dynamic range will be strongly-enhanced. This means that low bandwidth values result in greater image detail via a suppression of high-amplitude contrast modulations. Broad bandwidths result in greater contrast but also contain less image detail.

Enhancements

Enter a whole number between 0 and 100 into the Enhancement field or do the same using the scroll bar. The parameter determines the factor by which lesser intensity modulations are to be enhanced. Which value is the most suitable for differential contrast will depend on the bandwidth selected. Employing a narrow bandwidth in conjunction with strong enhancement will yield the greatest differential contrast. Image detail will be accentuated whereas larger image structures will ‘take a step back’ into the background.

Overflow

Enter the percentage of dark pixels to be set to black, and of light pixels to be set to white into the Overflow field. The last step involved with DCE-filter calculation is a spreading of intensity values applied to the whole intensity range. This is why you can enhance image contrast in the resulting image by simply clipping off intensity values located at either the higher or lower extremities (of the intensity value range) and setting them to 0 or 255 respectively (for 8-bit images). Theses intensity values are available for spreading the remaining gray/intensity values.

Percentages between 0 and 50 can be entered. When you select 50%, a gray-value image will look very similar to a binary image: colors will be either white or black.

Quality

Select the Quality check box to have image artifacts of the DCE-filter reduced. This will lengthen the time required to apply the filter. The DCE-filter can produce image artifacts that appear to be ‘scratches’. These are only found within larger solid-color image areas. They’re most noticeable when broad bandwidths and strong enhancement are in use.

Ramp optimize

Select the Ramp optimize check box to completely eliminate image artifacts resulting from the DCE-filter.

This check box can be used as a kind of supplement to the Quality check box. What will happen, however, is that all contrast either large in area or strong in intensity will be completely suppressed.

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