Histogram Tool

Toolbar:

Menu:   View > Histogram

Script:   showHistogram, setHistPos, setHistAttr, MeasHistogram

Use this command to display or hide the Histogram window for the Video window, an active image or selection. A histogram illustrates how intensity is distributed in the image by showing the number of pixels at each intensity level. Histogram data could be presented in graphic and tabular modes. In the graphic mode you can view information about a specific intensity point on the histogram by placing the cursor over it. You can also display information about a range of intensities by dragging and highlighting it with the mouse. Additional statistical information is available in the Advanced View mode.

The histogram chart could be displayed either in the Bar or Line form. This choice is available in ImageWarp Preferences. You can also select if you want the histogram data to be presented in the calibrated or non-calibrated form. If both axes of the Histogram are calibrated, the X-axis represents the intensity scale according to the current intensity calibration and the Y-axis measures the spatial area for each intensity value in spatial units. See Histogram Preferences for more details.

If you activate another image or change a selection in the current active image, the histogram will be automatically recomputed and updated. If the content of the active image changes as a result of image processing, the histogram will be updated as well. That allows for histogram animation during the execution of real-time scripts.

You can change the size of the Histogram window by positioning the cursor near an edge or corner and dragging the two-way arrow to the desired position.

The following options are available in the Standard View mode:

Y-Scale

Use this slider control located on the left side of the Histogram chart to change the scale of Y-axis of the histogram chart. The default range of Y-axis is determined by the largest frequency value.

Channel

For a color image, click the arrow on the right of the Channel box and select the channel for which you want to display the histogram (Red, Green, or Blue for the RGB color model; Hue, Luminance, and Saturation for the HLS color model; I-Phase and Quadrature for the YIQ color model). A correspondent color intensity scale will be displayed under the histogram chart. If the active image is gray, the box will appear dimmed with Luminance channel selected.

Cumulative

Select this check box to display the Histogram in a cumulative form. Each bin of cumulative histogram contains a number of pixels that have the marked value or a lesser value.

Gauss

Select this check box to display a Gaussian curve on the histogram chart. The Gaussian represents a normal distribution with the same mean and standard deviation the active image or its selection has.

Bins

Lets you specify the number of intervals used for histogram collection. By default, ImageWarp will divide the intensity scale into 256 bins. If you want the scale to be divided into another number of bins, type or select a desired value in the Bins box. Note that when you change this value, some precision will be lost due to averaging that occurs within the consolidated bins. If histogram data is saved to a file, the data will reflect the number of bins selected in the Bins box.

Min, Max

Let you specify minimum and maximum pixel values used to compute the histogram. By default, ImageWarp will set these values into 0 and 255 for a regular image, or into Display Range thresholds for a high-depth image.

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Press this button to switch the Histogram window into the Advanced View mode. The following controls will become available:

Bin

Displays the ordinal number of the bin pointed by the cursor on the histogram chart, or the range of selected bins. To highlight a specific range of bins, drag in the histogram chart.

Level

Displays the pixel level corresponding to the bin pointed by the cursor on the histogram chart, or the selected range of pixel levels.

Count

Displays the number of pixels in the bin corresponding to the intensity level pointed by the cursor on the histogram chart, or the total number of pixels in the selected range of levels. To highlight a specific range of levels, drag in the histogram chart.

Percent

Displays the cumulative percentile of pixels at or below the level pointed by the cursor. If the range of levels is highlighted, this box displays the percentile of pixels whose values belong to the selected range.

Median

Displays the middle value in the computed range of pixel values

Mean

Displays the average intensity for the active image or selection.

Deviation

Displays the standard deviation of intensity for the active image or selection. Deviation represents how widely intensity values vary.

Skewness

Displays the skewness of intensity distribution for the active image or selection. Deviation represents the symmetry of the histogram. A symmetric histogram has this value close to zero.

Kurtosis

Displays the kurtosis of intensity distribution for the active image. Kurtosis represents the size of the distribution tale. A normal distribution has kurtosis equal to zero.

Graph

Check this box to display the histogram data in graphic form.

Table

Check this box to display the histogram data in tabular form.

Copy to Grid   

Click this button to copy the histogram data to the Global Grid and display it. If the Global Grid already contains some data, they will be overwritten.

Save   

Use this button to store the current histogram data to a file. Histograms are saved as ImageWarp data tables containing the intensity intervals and the frequency reported for each interval. When you press the Save button, the standard file dialog box will appear. Enter the name of the file to which you want the histogram data stored, then click OK. Your histogram data will be written to the file. If the file with the selected name exists, the histogram data will be appended to the data already stored in the file.

Export to Excel   

Click this button to export the histogram data to Microsoft Excel's spreadsheet. You should have Microsoft Excel installed in your system in order to utilize this command.

Copy   

Click this button to copy the current histogram chart to the Windows Clipboard. After that you can paste the chart into other applications that accept standard clipboard formats. You can also press CTRL-C or CTRL-INS to perform this action.

Print   

Click this button to print the histogram and statistics data.

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Press this button to switch the Histogram window into the Standard View mode.