National Instruments IMAQTM 用户手册

2.

Improve the image in the frequency domain with a lowpass or highpass 
frequency filter. Specify which type of filter to use with 

CWIMAQVision.CxAttenuate

 or 

CWIMAQVision.CxTruncate

. 

Lowpass filters smooth noise, details, textures, and sharp edges in an 
image. Highpass filters emphasize details, textures, and sharp edges in 
images, but they also emphasize noise.

•

Lowpass attenuation—The amount of attenuation is directly 
proportional to the frequency information. At low frequencies, 
there is little attenuation. As the frequencies increase, the 
attenuation increases. This operation preserves all of the zero 
frequency information. Zero frequency information corresponds 
to the DC component of the image or the average intensity of 
the image in the spatial domain. 

•

Highpass attenuation—The amount of attenuation is inversely 
proportional to the frequency information. At high frequencies, 
there is little attenuation. As the frequencies decrease, the 
attenuation increases. The zero frequency component is removed 
entirely.

•

Lowpass truncation—Specify a frequency. The frequency 
components above the ideal cutoff frequency are removed, and 
the frequencies below it remain unaltered.

•

Highpass truncation—Specify a frequency. The frequency 
components above the ideal cutoff frequency remain unaltered, 
and the frequencies below it are removed.

3.

To transform the image back to the spatial domain, use 

CWIMAQVision.InverseFFT

. 

CWIMAQVision.ReplaceComplexPlane

 and 

CWIMAQVision.ExtractComplexPlane

 allow you to access, process, 

and update independently the magnitude, phase, real, and imaginary 
planes of a complex image. You can also convert a complex image to 
an array and back with 

CWIMAQImage.ImageToArray

 and 

CWIMAQImage.ArrayToImage

.