Correct background  
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Menu:   Processing > Background… > Correct  
Script:   bkCorrect  

Use this function to correct an image background and prepare an image for optical density and transmission measurements. Uneven background, or shading is usually caused by non-uniform illumination, irregular camera response, electronic noise and optics imperfections.

In general, to perform the background correction you have to prepare two auxiliary images: dark field and bright field. Dark field is a background image captured with no light transmitted through the camera lens, and the bright field is a background image captured with the maximum light transmitted and no objects in the filed of view. It is recommended to use Average mode of the Capture
command to acquire background images. While capturing the bright field image you should adjust the light intensity so that it stays just below the saturation level of the camera. That will provide the maximum dynamic range for the image acquisition. To control the saturation for black and white cameras, use the Saturated palette in the Video window

The correction algorithm is based on the following formula:


bkcorrect

where

Ix,y    is a pixel value of the original image
Bx,y    is a pixel value of the dark field image
Wx,y    is a pixel value of the bright field image
Wmax    is a maximum value of the bright field image
Cx,y    is a new pixel value of the corrected image

After the image is corrected,
Wmax value is stored as the assigned background for further use in optical density and transmission measurements.

You can use only one auxiliary image to perform the background correction. For instance, in the experiments with fluorescent phenomena only the dark field image should be used for correction.

The following options are available for Background Correction:

Input
 
Displays the number of the frame containing the image to be corrected. If you want to correct the background of another image, type or select the corresponding value.  

Dark
 
Displays the number of the frame containing the dark field image. The Subtract option must be selected in order for the dark field image to be processed.  
 
Bright
 
Displays the number of the frame containing the bright field image. The Even option must be selected in order for the bright field image to be processed.  

Output
 
Displays the number of the frame in which the corrected image will be created. Depending on the Preferences. ImageWarp will set it either to the first available value or to the Input frame number. Type or select another value if you want the output image to be created in a different frame.  
 
Subtract
 
Select this option if you want to perform the dark field correction. If this box is unchecked, the additive component of the correction algorithm is disregarded.  
 
Even
 
Select this option if you want to perform the bright field correction. If this box is unchecked, the multiplicative component of the correction algorithm is disregarded.  

Preview
 
Select this check box to watch the Preview of the output image.