In its narrow sense, image processing refers to a transform of an image into another. All such functions of PixeLINK Capture are located in two groups of popup menus, Adjust and Enhancement. As their names imply, they are tools to adjust the brightness, color, orientation and so on of an image or to enhance an image in a specific way. The Min, Max and Average commands within Field menu may also work to create an image from two or more images.
Most of image processing commands can be executed by simply selecting menu items or clicking the corresponding toolbar buttons if available. The behavior of some of these commands may be customized by respective separate commands which bring up dialog boxes with entries for configuration. The above two types of commands are referred to as Category 1 and Category 2 commands.
The menu item Adjust -> Interactive brings up a dialog box and operates on the active image from the dialog. This command belongs to Category 3 and is the only command in this category.
The menu item Enhance -> Color Balance starts a processing that requires an additional mouse click to finish. After selecting the menu item or clicking on the corresponding toolbar button, the mouse cursor changes its shape to a suction tube to indicate the processing in progress. Click on a pixel that should be colorless and the color aberrations will be corrected accordingly. This command belongs to Category 4 and is the only command in this category.
The following table summarizes the command categories.
|
Category |
Menu |
Menu Item |
Customizing Command |
|
3 2 1 |
Adjust |
Interactive… |
|
|
More -> Intensity |
Increment Options | ||
|
More -> Saturation |
|||
|
More -> Hue |
|||
|
Less -> Intensity |
|||
|
Less -> Saturation |
|||
|
Less -> Hue |
|||
|
Mirror -> Horizontal |
| ||
|
Mirror -> Vertical |
| ||
|
Mirror -> Diagonal |
| ||
|
Rotate -> Counterclockwise 90 degree |
| ||
|
Rotate -> Clockwise 90 degree |
| ||
|
Rotate -> 180 degree |
| ||
|
2 1 2 1 4 1 |
Enhance |
Flatfield Correction |
Flatfield Correction Options |
|
Denoise |
| ||
|
Remove Bad Pixels |
| ||
|
Unsharp |
Unsharp Options | ||
|
Max Contrast |
| ||
|
Sketch |
| ||
|
Adaptive Edge Emphasis |
| ||
|
Equalization |
| ||
|
Amplitude Depletion |
| ||
|
Darkfield |
| ||
|
Color Balance |
| ||
|
Photometric Transform -> Monochrome |
| ||
|
Photometric Transform -> Negative |
|
Each of these values is in the range 0~255. Each channel may be changed independently of other channels but the adjustment uniformly applies to all pixels in the image. Note hue is cyclic with a period of 256. When saturation or intensity is set to a value greater than 255 or less than 0 it will be clipped.
Adjust -> Interactive
Adjust -> More -> Hue
Adjust -> More -> Saturation
Adjust -> More -> Intensity
Adjust -> Less -> Hue
Adjust -> Less -> Saturation
Adjust -> Less -> Intensity
The step size of each of the above commands is defined in Adjust -> Incremental Options…which brings up the following dialog box.
New values for hue, saturation and intensity increments may be specified separately and will be effective in the execution of next command. The step size should be non-negative integer less than 256. These parameters will be remembered across sessions until you change them again.
It is possible to change the way an image is viewed without lose of details. This group of functions is self-explanatory.
Adjust -> Rotate -> Counterclockwise 90 degree Adjust -> Rotate -> Clockwise 90 degree
Adjust -> Rotate -> 180 degree
Adjust -> Flip -> Horizontally
Adjust -> Flip -> Vertically
When the specimen is not illuminated uniformly across the whole field of view, it is often necessary to correct this unevenness for either aesthetic or computational purpose. The following command is a convenient means of uneven illumination correction.
Enhance -> Flatfield Correction
To customize, select Enhance -> Flatfield Correction Options… to bring up the following dialog.
The Homogenous Radius is a value to indicate illumination variation. A great
value means a slight change of light intensity and a small value means an abrupt change. The default value 31 usually works well but you may experiment for an optimal setting.
It is possible to correct to a certain extent the random deviation of pixels from their true value.
Enhance -> Denoise
You may execute this command more than once to suppress severe noise.
Some pixels of the camera sensor may stop functioning after some time of use. The following command is provided to detect and replace bad pixels by reasonable approximations.
Enhance -> Remove Bad Pixels
This is a classic image enhancing method extended and generalized. To uncover minute details execute command.
Enhance -> Unsharp
For the full power of this function, you may select Enhance -> Unsharp Options… to bring out and fill the following dialog.
Mask Radius determine the size of the spatial filter to separate the image into low-frequency and high-frequency parts. The default value of 11 should work fine in most cases but you may specify a greater integer for a lower cutoff frequency or a smaller integer for a higher frequency.
Latitude Reduction is a real number between 1 and 0 to indicate the degree of shrinkage of total dynamic range of the image. With a smaller overall dynamic range local features are displayed with more contrast.
High Boost is a real number no less than 1. In contrast to reduction of dynamic range, a greater value of High Boost enhances the details directly.
Also specify a value within the range 0~1 for Combine, which dictates the way how the enhanced part of the image is projected back to the unchanged part. A value of 0 means the enhancement is independent of original pixel value while a value of 1 means the greater pixel value is modified to a greater degree.
It is advised to keep the default values for the last three parameters. You may execute the command more than one time for a greater degree of enhancement.
The following command may extend an image to its maximum contrast without loss of information whatsoever.
Enhance -> Max Contrast
This command creates a pencil drawing from an image.
Enhance -> Sketch
Human eyes are most responsive to edges contained in an image and noise in flat areas. The following command boosts edge while leaving smooth area unchanged.
Enhance -> Adaptive Edge Emphasis
Histogram equalization is one of the basic image contrasting techniques. It works by re-arrange the intensities of each pixel so that number of pixels is roughly the same for each intensity value. The following command implements this operation.
Enhance -> Equalization
An image is often interpreted as a distribution of light intensities. Another, perhaps more useful understanding is a distribution of patterns of various amplitudes. When the relative strength of the patterns is ignored, the pattern themselves are revealed in the maximum possible way. The following command is for this purpose.
Enhance -> Amplitude Depletion
The darkfield imaging mode helps reveal height variations of the specimen surface. If you have only brightfield mode on your microscope you may
simulate a darkfield image from a brightfield image using the following command.
Enhance -> Darkfield
A color camera records only relative intensities of light in three frequency bands and may not correspond exactly to human perception. It is advised to adjust the camera gain settings to match the digital image to optical image we see through oculars, if possible. There are also occasions where the light source temperature shows on the specimen which we want to remove. The following command is designed for post-capture color balancing.
Enhance -> Color Balance
For this command to work, you will need to pick out a pixel within the image which should be gray but which now shows a tint. The light source or camera aberrations could then be inferred and corrected.
When it is necessary to convert a color image to a monochromatic representation or to convert an image to its negative, you may use the following commands.
Enhance -> Photometric Transform -> Monochrome Enhance -> Photometric Transform -> Negative