odRatio

odRatio ( integer Input, integer Bright, integer Dark, integer Output )

Use this function to generate a floating point image whose pixels represent the optical density values.

In general, to generate the optical density image, two auxiliary images should be prepared: 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 (no specimen or objects in the filed of view). It is recommended to use the grabAvrg function to acquire background images. While capturing the bright field image, the user 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.

The resulting pixel values are based on the following formula:


where

I_x,y    is a pixel value of the original image
B_x,y    is a pixel value of the dark field image
W_x,y    is a pixel value of the bright field image
OD_x,y    is a pixel value of the resulting Optical Density image


Parameters

Input

An integer between 0 and 116 specifying the input image frame number. A value of 0 represents the DMA memory buffer of the video device. Values in the range of 100-116 correspond to hidden frames.

Output

An integer between 1 and 116 specifying the output image frame number. Values in the range of 100-116 correspond to hidden frames.

Dark

An integer between 0 and 116 specifying the number of the frame that contains a dark field image. Values in the range of 100-116 correspond to hidden frames. If this parameter is zero, only the bright field image will be used in calculations.

Bright

An integer between 0 and 116 specifying the number of the frame that contains a bright field image. Values in the range of 100-116 correspond to hidden frames.

Error flags

ERR_OK

The flag set if successful.

ERR_FAILED

The flag set if failed.

Example

This set of statements prompts the user to capture a dark and white field, and then continuously generates an optical density image in frame #1.

Dark=102

Bright=101

Print "Open Video window"

Input "Press Enter to capture dark field"

grabIm (Dark)

Input "Press Enter to capture bright field"

grabIm (Bright)

Input "Press Enter to display corrected video"

do

grabIm (100)

odRatio (100, 101, 102, 1)

loop

Example

To perform the OD measurements on the image generated by this function use linear intensity measurements (GrayAvrg, GraySD, GrayI, etc.) rather than their OD counterparts (OptdAvrg, OptdSD, OptdI). The latter will implement unnecessary logarithmic conversion, which is already done by odRatio. See the Measure section of ImageWarp User's Guide for more details.