National Instruments IMAQTM 用户手册

linear filter

A special algorithm that calculates the value of a pixel based on its own 
pixel value as well as the pixel values of its neighbors. The sum of this 
calculation is divided by the sum of the elements in the matrix to obtain 
a new pixel value.

logarithmic function

Increases the brightness and contrast in dark regions of an image and 
decreases the contrast in bright regions of the image.

logic operators

The image operations AND, NAND, OR, XOR, NOR, XNOR, difference, 
mask, mean, max, and min.

lossless compression

Compression in which the decompressed image is identical to the original 
image.

lossy compression

Compression in which the decompressed image is visually similar but not 
identical to the original image.

lowpass attenuation

Applies a linear attenuation to the frequencies in an image, with no 
attenuation at the lowest frequency and full attenuation at the highest 
frequency.

lowpass FFT filter

Removes or attenuates high frequencies present in the FFT domain of an 
image.

lowpass filter

Attenuates intensity variations in an image. You can use these filters to 
smooth an image by eliminating fine details and blurring edges.

lowpass 
frequency filter

Attenuates high frequencies present in the frequency domain of the image. 
A lowpass frequency filter suppresses information related to fast variations 
of light intensities in the spatial image.

lowpass truncation

Removes all frequency information above a certain frequency.

L-skeleton function

Uses an L-shaped structuring element in the skeleton function.

luma

The brightness information in the video picture. The luma signal amplitude 
varies in proportion to the brightness of the video signal and corresponds 
exactly to the monochrome picture.

luminance See luma.

LUT

Lookup table. A table containing values used to transform the gray-level 
values of an image. For each gray-level value in the image, the 
corresponding new value is obtained from the lookup table.