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Glossary of Imaging Terms
Ernst Abbe's specification for the limit of resolution of a diffraction-limited microscope. Abbe's reports that an object with a particular spacing in the specimen is resolved when the numerical aperture (NA) of the object lens is large enough to capture the first-order diffraction pattern produced by the object at the wavelength employed.
Failure of an optical or electron-optical lens to produce exact geometrical (and chromatic) correspondence between an object and its image. Aberrations arise from video cameras and cathode ray tubes when the electrostatic or electromagnetic lens does not bring the electron beam into sharply focused points uniformly on the target or screen; this can also happen when the beam is deflected.
A procedure to subtract away persistent noise patterns generated in the optical system. Background subtraction results in the local alteration of the value of each pixel, depending on the intensity of the corresponding pixel in the background image. The resultant is that the non-uniformaties in the detector or illumination (dirt and non-uniform illumination observed in transmitted-light microscopy) can be compensated for by storing a background image of an empty microscope field. See Subtract Bias and Flat-Fielding.
A readout of the camera's CCD without an exposure time. The readout number is used to determine the "read noise" the amount of signal generated by reading the accumulated pixel charge of the CCD.
The combination of stored charges from several pixels in a CCD to give the equivalence of a single larger pixel. For example, a 2 X 2 bin means 2 pixels in the X and 2 pixels in the Y are combined to form one larger pixel. Binning gives you the advantage of boosting low signals, however, binning MAY reduce resolution.
A corresponding table to translate data intensity values into displayed colors. The CLUT contains 256 entries, and in each entry there is a set of three numbers that correspond the red, green and blue (RGB).
The sectioning capability of a particular lens. The distance between the closest and farthest objects in focus within a field of view of a lens at a particular focus and with given settings. The depth of field varies with the focal length of the lens and its f-stop setting or numerical aperture and with the wavelength of light.
For electronic equipment and for photographic emulsions, the ratio of the maximum signal level to the minimum signal level that introduces no more than acceptable levels of signal amplitude distortions. In other words dynamic range is the ability of an electronic detector to register a wide range of tonal values -- something from near white to near black.
This is a technique for compensating for defects or non-uniformities in a camera or non-uniform lighting. This technique is more accurate than simply subtracting the background. IPLab uses the Image Ratio command in the Enhance menu to perform a variety of image corrections or calibrations, including flat fielding.
The amount of signal amplification. Increasing a camera's gain control will boost the contrast and effectively the brightness of the image.
An image processing operation that uses operators such as addition, subtraction, multiplication and division. The operations are performed pixel by pixel, so that the sum of the two images simply contains pixels whose brightness values are the sums of the corresponding pixels in the original images. In IPLab the Image Arithmetic command combines two images to produce a third. These arithmetic operations produce a single output by performing point by point operations of the two input data windows.
Image ratios are used in a variety of applications to correct or calibrate image data.
An image processing technique that replaces the value of each data element (pixel) with a value computed by a weighted sum of the values of neighboring data elements (pixels) in the input, and perhaps the values of some data element already computed in the output.
Median Filter is similar to the Linear Filter in that each pixel is changed based on the values of nearby pixels. The pixel value is changed to have the median value of the pixels within the neighborhood, i.e., half the pixels in the neighborhood will have values above the median and half will have values below the median. The median filter is often used to remove "salt-and-pepper" noise from an image. It eliminates isolated bright pixels which may ne due to stray photons hitting the detector of your camera.
A process that displays all image data by mapping data values between 0 and 255. Display Normalization does not affect the data element values, it only alters the display values (the way you see the data). Normalization maps pixels with values greater than or equal to the White parameter so that they are displayed as white, and pixels with values less than or equal to the Black parameter so that they are displayed as black. All the data values between Black and White are mapped either linearly or through a gamma curve to gray values.
The half angle of the cone of light accepted by the objective lens times the refractive index of the medium between the specimen and the lens. The higher the half angle of acceptance, the higher the NA, the higher the angle of light acceptance, and the lower the depth of field.
Picture element (pix for picture, and el for element). A single, finite-sized element of a digitized video picture. A pixel is defined by its x and y coordinates and its gray level (luminance), commonly expressed by binary numbers.
The assigning of selected colors to levels of gray values in order to designate area with similar gray values or enhance subtle differences of gray values in the picture. The human eye can only distinguish about 30 shades of gray in a monochrome image, however, we can distinguish hundreds of different colors. It is simply easier to identify a particular object as "the dark green blob" instead of "the medium gray blob".
Named after Lord Rayleigh, the criterion defines the limit of resolution of a diffraction-limited optical instrument. It is the condition that arises when the center of one diffraction pattern is superimposed with the first minimum of another diffraction pattern to produce by a point source equally bright as the first.
A measure of how fine a detail can be detected, in terms of distance in space or passage of time. Optical resolution refers to the measurement of the distance between (or frequency of) line pairs, whereas in video resolution refers to the number of black and white line counts. Simply put: resolution is the minimum distance that two objects must be separated to be discerned as two separate objects.
Resolution is determined by the Rayleigh criteria:
Criteria = 1.22 * wavelength of light / (NA(condenser) + NA (objective))
Resolution is determined by the Rayleigh criteria:
Criteria = 1.22 * wavelength of light / (NA(condenser) + NA (objective))
The ROI (Region of Interest) is the region or area of the image that you are interested. In practice, the ROI is the area of the image, any collection of connected pixels, that you have selected. The ROI and the blinking, dashed selection line that surrounds the ROI are synonymous.
The IPLab Rotate and Scale command performs fractional geometric rotation and scaling and places the result into an image window with new dimensions which are big enough to hold the resulting image. You may enter different values for the X and Y direction scaling, or lock them together. Whenever fractional scaling and rotation are performed, some form of interpolation must be used. The Nearest Neighbor option is faster, while the Bilinear Interpolation option often gives a visually more pleasing result, because it smoothes jagged edges. The image is rotated and scaled about the center of the window.
The Alert command instructs you perform a specific task or lets you know that IPLab is going to perform a specific task.
This command in a script will prompt the user to enter numeric values. The numeric values will be used be other commands in the script.
In conjunction with the Label command, allows the script to use conditional branching.
Inserts a user defined label into the script. These labels are used in conjunction with the If, Jump
Provides simple backward looping capabilities. The user can specify where to loop to and the number of iterations to loop.
The Query command will prompt the user with a two or three part question. This command is generally associated with the If command. The path that script takes depends on the answer to the Query.
The process of separating background pixels from pixels which are in the target area. Often the background and target differ in intensity, so one of the most common ways of performing segmentation is by thresholding the intensity values. In IPLab the segmentation command can be found in the Analyze menu.
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