McIDAS-X User's Guide
Version 2023.1

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IMGPROBE

Lists or plots image data for a region of the displayed image.

Format

IMGPROBE option region unit [keywords]

Parameters

Keywords

Keywords valid with CONT option

Keywords valid with HIST and PLOT options

Keywords valid with NORM option

Keywords valid with Interactive and Batch Modes

Remarks

IMGPROBE lists or plots data for a region of the image displayed on the current frame or an image specified in the DATASET keyword. When using a displayed image, the image file must be present on disk (as opposed to workstation memory) because IMGPROBE uses data directly from the image file.

The following combinations of option and region parameters are valid:

When you use the PLOT option with the BOX region, the x-axis of the line plot lists the pixel numbers in the box from left to right and top to bottom. Pixel number 1 is the upper-left data point, and the largest pixel number is the bottom-right data point.

When you use the LIST option with the BOX or LINE region, the output is listed in Output Blocks. There is no limit to the number of lines in an Output Block, so the output is divided into multiple Output Blocks only if it's too wide to fit in the text frame. The number of Output Blocks depends on the number of data points in each line of output and the calibration unit selected. For example, you can fit more brightness values across the text frame than IR radiance values. In the output for the BOX region, each successive Output Block is located to the right of the previous Output Block.

If you specify an even number for the line or ele parameter of the SIZE keyword, it is not possible to place an equal number of lines or elements on each side of the cursor center. The bottom line or right column of elements is omitted. For example, if the cursor is positioned at line 100 and element 200 and you specify SIZE=50 50, the data points used are those in a box covering lines 75 to 124 and elements 175 to 224.

When using the CONT option with the BOX region, there must be less than 10,000,000 data points in the region. When using a BOX region with any other option, there must be less than 30,000,000 data points in the region. To calculate this number, you must know the image blowup or blowdown factor. If the image is displayed:

• at the image's resolution (blowup or blowdown factor of 1), use the formula: region height x region width
• with a blowup factor of M, use the formula:
  {[(region height - 1)/M ] + 1} x {[(region width - 1)/M ] + 1}
  Note: if a division in the formula yields a decimal value, it is truncated before adding 1 and multiplying the terms
• with a blowdown factor of N, use the formula: (region height x N) x (region width x N)

For example, a 10 by 100 region size over a 1 km resolution image displayed with a blowup/blowdown factor of 1 contains 1000 data points. If the image is displayed at 2 km resolution (blowdown factor of 2), the region contains 4000 data points. If it is displayed at 0.5 km resolution (blowup factor of 2), the region contains 250 data points.

If you specify a BOX or POINT region, MODE=N, and a dataset in the DATASET keyword, you must specify the location with the LATLON, LINELE, or STATION keyword. If it is a BOX region, you must also specify the region size with the SIZE keyword.

If you specify MODE=N but do not specify the DATASET keyword, the cursor is moved to the location specified in the LATLON, LINELE or STATION keyword.

Use the IMGPROBE LIST POINT command to determine valid options for the unit parameter.

You can enter numeric values in the EXCLUDE keyword using the list format (value1 value2 value3 etc.) and/or range format (x-yBn where x and y are the beginning and ending values, and n is the increment). If you don't specify an increment, all real numbers from x through y are excluded. For example, EXCLUDE=0 126-129 255 excludes 0, all values from 126 through 129, and 255; EXCLUDE=0 126-129B1 255 excludes 0, 126, 127, 128, 129 and 255; EXCLUDE=0 126-130B2 255 excludes 0, 126, 128, 130 and 255; EXCLUDE=-12--1 excludes all values from -12 through -1; EXCLUDE=150-140 excludes all values greater than 150 and all values less than 140.

When using the NORM option, the BRIT values in the output are the original BRIT values of the min/max calibrated values before being stretched from 0 to 255. The reported Bin Size value is the interval in calibrated values used when stretching the BRIT values from 0 to 255. Use FORM=ALL to see how the calibrated values are mapped to the new BRIT values.

In satellite imagery, the latitude/longitude location of a pixel is determined by where the instrument is pointing. It is often the center of the field of view of the instrument, though the instrument vendor can define the geolocation any way they want. Regardless, in McIDAS it is assumed to be the center. For geographic projections, a pixel is just a point. So there is no notion of dimensionality, and it is again assumed to be the center. For users collocating pixels from different satellites, a larger issue is the viewing angle differences. They can be on the order of several pixels near nadir to tens of pixels away from nadir.

Examples

IMGPROBE

This entry lists information for one or more data points at the center of the cursor, including all calibration units for the image. The command is interactive, so you are prompted to select each point by moving the cursor and pressing the right mouse button or Alt G. Press Alt Q to quit.

IMGPROBE LIST LINE

This entry lists information for the data points along one or more lines. You are prompted to define each line's beginning and ending points using the mouse; then, press Alt Q to quit. The lines are not drawn on the frame.

IMGPROBE LIST LINE OUTLINE=YES 2

This entry lists information for the data points along one or more lines. You are prompted to define each line's beginning and ending points using the mouse; then, press Alt Q to quit. The lines are drawn on the frame in graphics color level 2.

IMGPROBE STAT BOX OUTLINE=YES BAND=4 EXCLUDE=255 SPACE MODE=N

This entry draws an outline around the data points in the region defined by the cursor limits and lists the statistical values for band 4 of those data points. Pixels without navigation or with a brightness value of 255 are not included in the statistical analysis.

IMGPROBE CONT BOX BRIT SIZE=200 300 CINT=10 MODE=N

This entry contours brightness values of the data points in a 200 by 300 pixel region centered at the cursor position. Contours are drawn at an interval of every 10 brightness values.

IMGPROBE PLOT LINE OUTLINE=YES 5 COLOR=4

This entry draws a line plot of the data point values along a line. You are prompted to define the line's beginning and ending points using the mouse. The plot is drawn in graphics color level 4. The line is drawn in graphics color level 5. The command is interactive, so you can draw additional line plots by selecting each line's beginning and ending points using the mouse. Note, however, that the graphics are erased each time you select a new beginning point since EG=YES is the default.

IMGPROBE HIST BOX SU=WARM COLOR=2

This entry draws a histogram of the values of the data points in the region defined by the cursor limits. The histogram is drawn in graphics color level 2. The values for the histogram are those that would be present if the image was displayed using the stretch table WARM. The command is interactive, so you can draw additional histograms by selecting new box regions using the mouse. Note, however, that the graphics are erased each time you select a new region since EG=YES is the default.

IMGPROBE HIST BOX TEMP XRANGE=200 300 YRANGE=0 100 LENGTH=.1 DATASET=GOES/IR.5 MODE=N LATLON=40 100 SIZE=50 50

This entry draws a histogram of the temperatures of the region's data points. The region is a 50- by 50-pixel box centered at 40°N, 100°W on the image in position 5 in dataset GOES/IR. The histogram's x-axis range is 200 to 300 degrees Kelvin, and the y-axis range is 0 to 100 occurrences. The length of the class interval is 0.1 degrees Kelvin.

IMGPROBE NORM BOX TEMP MODE=N

This entry computes a histogram normalization in the region defined by the cursor limits and applies the new enhancement to the image.

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