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Analyze Menu

Measure

Based on the selection type, calculates and displays either area statistics, line lengths and angles, or point coordinates. Area statistics are calculated if there is no selection or if a subregion of the image has been selected using one of the first four tools in the tool bar. Calculates line length and angle if a line selection has been created using one of the three line selection tools. Records coordinates if one or more points have been defined using the point selection tool. Use the Analyze>Set Measurements command to specify what area statistics are recorded.

[Measurements]

With RGB images, results are calculated using brightness values. RGB pixels are converted to brightness values using the formula V=(R+G+B)/3, or V=0.299R+0.587G+0.114B if "Weighted RGB Conversions" is checked in Edit>Option>Conversions. The default weighting factors are the ones used to convert to from RGB to YUV, the color encoding system used for analog television. The weighting factors can be changed using the setRGBWeights macro function.

With line selections, the following parameters can be recorded: length, angle (straight lines only), mean, standard deviation, mode, min, max and bounding rectangle (v1.34l or later). The mean, standard deviation, etc. are calculated from the values of the pixels along the line.

To export the measurements as a tab-delimited text file, select File>Save As>Measurements from the ImageJ menu bar or File>Save As from the "Results" window menu bar. Copy the measurements to the clipboard by selecting Edit>Copy All from the "Results" window menu bar. You can also save measurements by right-clicking in the Results window and selecting Save As or Copy All from the popup menu.

The width of the columns in the "Results" window can be adjusted by clicking on and dragging the vertical lines that separate the column headings.

Analyze Particles...

This command counts and measures objects in binary or thresholded images. It works by scanning the image or selection until it finds the edge of an object. It then outlines the object using the wand tool, measures it using the Measure command, fills it to make it invisible, then resumes scanning until it reaches the end of the image or selection. Press the esc key to abort this process. Use Image>Adjust>Threshold to threshold an image.

[Example]

Use the dialog box to configure the particle analyzer. Particles outside the range specified in the Size field are ignored. Enter a single value in Size and particles smaller than that value are ignored. Particles with circularity values outside the range specified in the Circularity field are also ignored. The formula for circularity is 4pi(area/perimeter^2). A value of 1.0 indicates a perfect circle. Note that the Circularity field was added in ImageJ 1.35e.

[Dialog]

Select Outlines from the "Show:" popup menu and ImageJ will open a window containing numbered outlines of the measured particles. Select Masks to display filled outlines of the measured particles or Ellipses to display the best fit ellipse of each measured particles.

[Example]

Check Display results to have the measurements for each particle displayed in the "Results" window. Check Clear Results to erase any previous measurement results. Check Summarize to display, in a separate window, the particle count, total particle area, average particle size, and area fraction. Check Exclude on Edges to ignore particles touching the edge of the image or selection.

Check Flood Fill and ImageJ will define the extent of each particle by flood filling instead of by tracing the edge of the particle using the equivalent of the wand tool. Use this option to exclude interior holes and to measure particles enclosed by other particles. The following example image contains particles with holes and particles inside of other particles.

[Examples]

The Record Starts option allows plugins and macros to recreate particle outlines using the doWand(x,y) function. The CircularParticles macro demonstrates how to use this feature.

Summarize

For each column in the results table, calculates and displays the mean, standard deviation, minimum and maximum of the values in that column.

Clear Results

Erases the results table and resets the measurement counter.

Set Measurements...

Use this dialog box to specify which measurements are recorded by Analyze>Measure and Analyze>Analyze Particles.

[Measurements]

Area - Area of selection in square pixels. Area is in calibrated units, such as square millimeters, if Analyze>Set Scale was used to spatially calibrate the image.

Mean Gray Value - Average gray value within the selection. This is the sum of the gray values of all the pixels in the selection divided by the number of pixels. Reported in calibrated units (e.g., optical density) if Analyze>Calibrate was used to calibrate the image. For RGB images, the mean is calulated by converting each pixel to grayscale using the formula gray=0.299red+0.587green+0.114blue or the formula gray=(red+green+blue)/3 if "Unweighted RGB to Grayscale Conversion" is checked in Edit>Options>Conversions.

Standard Deviation- Standard deviation of the gray values used to generate the mean gray value.

Modal Gray Value - Most frequently occurring gray value within the selection. Corresponds to the highest peak in the histogram.

Min & Max Gray Level - Minimum and maximum gray values within the selection.

Centroid - The center point of the selection. This is the average of the x and y coordinates of all of the pixels in the image or selection. Uses the X and Y Results table headings.

Center of Mass - This is the brightness-weighted average of the x and y coordinates all pixels in the image or selection. Uses the XM and YM headings. These coordinates are the first order spatial moments.

Perimeter - The length of the outside boundary of the selection.

Bounding Rectangle - The smallest rectangle enclosing the selection. Uses the headings BX, BY, Width and Height, where BX and BY are the coordinates of the upper left corner of the rectangle.

Fit Ellipse - Fit an ellipse to the selection. Uses the headings Major, Minor and Angle. Major and Minor are the primary and seconday axis of the best fitting ellipse. Angle is the angle between the primary axis and a line parallel to the x-axis of the image. Note that ImageJ cannot calculate the major and minor axis lengths if Pixel Aspect Ratio in the Set Scale dialog is not 1.0.

Circularity - 4pi(area/perimeter^2). A value of 1.0 indicates a perfect circle. As the value approaches 0.0, it indicates an increasingly elongated polygon. Values may not be valid for very small particles.

Feret's Diameter - The longest distance between any two points along the selection boundary. Also known as the caliper length. The Feret's Diameter macro will draw the Feret's Diameter of the current selection on the image.

Integrated Density - The sum of the values of the pixels in the image or selection. This is equavalent to the product of Area and Mean Gray Value. The Dot Blot Analysis example demonstrates how to use this option to analyze a dot blot assay.

Median- The median value of the pixels in the image or selection.

Skewness- The third order moment about the mean. The documentation for the Moment Calculator plugin explains how to interpret spatial moments.

Kurtosis- The fourth order moment about the mean.

Area Fraction- The percentage of pixels in the image or selection that have been highlighted in red using Image>Adjust>Threshold. For non-thresholded images, the percentage of non-zero pixels.

Limit to Threshold - If checked, only thresholded pixels are included in measurement calculations. Use Image>Adjust>Threshold to set the threshold limits.

Display Label - If checked, the image name and slice number (for stacks) are recoded in the first column of the results table.

Invert Y Coordinates - If checked, the XY origin is assumed to be the lower left corner of the image window instead of the upper left corner.

Redirect To - The image selected from this popup menu will be used as the target for statistical calculations done by the Measure and Analyze Particles commands. The Redirect To feature allows you to outline a structure on one image and measure the intensity of the corresponding region in another image. With ImageJ 1.35d or later this feature also works with stacks.

Decimal Places - This is the number of digits to the right of the decimal point in real numbers displayed in the results table and in histogram windows.

Set Scale...

Use this dialog to define the spatial scale of the active image so measurement results can be presented in calibrated units, such as millimeters. Before using this command, use the straight line selection tool to make a line selection that corresponds to known distance. Then, bring up the Set Scale dialog, enter the known distance and unit of measurement, then click OK. ImageJ will have automatically filled in the Distance in Pixels field based on the length of the line selection.

[Dialog]

Set Distance in Pixels to zero to revert to pixel measurements.

Setting Pixel Aspect Ratio to a value other than 1.0 enables support for different horizontal and vertical spatial scales, for example 100 pixels/cm horizontally and 95 pixels/cm vertically. To set the pixel aspect ratio, measure the width and height (in pixels) of a digitized object with a known 1:1 aspect ratio. Enter the measured width (in pixels) in Distance in Pixels. Enter the known width in Known Distance. Then calculate the aspect ratio by dividing the width by the height and enter it in Pixel Aspect Ratio.

When Global is checked, the scale defined in this dialog is used for all images instead of just the active image.

Two examples of how to use the Set Scale command are available: Area Measurements (PDF) and DNA Contour Length Measurement.

Calibrate...

Use this dialog box to calibrate an image to a set of density standards, for example radioactive isotope standards or a calibrated optical density step tablet. Before using this command, use Analyze>Clear Results to reset the measurement counter and use one of the selection tools and Analyze>Measure to record the mean gray value of each of the standards. There is an example that shows how to calibrate to an optical density step tablet.

[Dialog]

When finished making the measurements, select Analyze>Calibrate to display the Calibrate dialog box. To calibrate the image, enter the known standard values in the right column, select a curve fitting method from the popup menu, enter the unit of measurement, and click OK. ImageJ will then display the calibration function.

[Function]

If the calibration function is not satisfactory, bring up the Calibrate dialog box again and select a different curve fitting method.

Rodbard is a four parameter general curve fit function proposed by David Rodbard at NIH. The form of the equation is:

y = d + (a - d) / (1 + (x/c)^b)
Selecting Uncalibrated OD from the popup menu causes ImageJ to convert gray values to uncalibrated optical density values using the function
Uncalibrated OD = log10(255 / PixelValue)
You do not need to measure OD standards or enter known OD values to enable this feature.

Histogram

Calculates and displays a histogram of the distribution of gray values in the active image or selection. The x-axis represents the possible gray values and the y-axis shows the number of pixels found for each gray value. The total pixel count is also calculated and displayed, as well as the mean, modal, minimum and maximum gray value.

[Histogram]

Use the Save or Copy buttons to save the histogram data. Click on Log to display a log-scaled version of the histogram. The number to the right of Value:, which changes as you move the cursor, is the grayscale value corresponding to the x-axis cursor position and Count: is the number of pixels that have that value.

With RGB images, the histogram is calculated by converting each pixel to grayscale using the formula gray=0.299red+0.587green+0.114blue or the formula gray=(red+green+blue)/3 if "Unweighted RGB to Grayscale Conversion" is checked in Edit/Options/Conversions. With 16-bit images, the range of gray values between the Min and Max values is divided into 256 bins. With 32-bit images, the number of bins is specified in this dialog box:

[Dialog]

Check Use min/max and the x-axis range is determined by the minimum and maximum values in the image or selection, or specify X Min and X Max values to fix the x-axes range. Enter a Y Max value to fix the y-axis range or enter "Auto" to have the range determined by the largest bin count. In ImageJ 1.35a or later, hold down the alt key (or press alt-h) to use this dialog with 8-bit, 16-bit and RGB images.

Plot Profile

Displays a two-dimensional graph of the intensities of pixels along a line within the image. The x-axis represents distance along the line and the y-axis is the pixel intensity.

[Plot]

For rectangular selections, displays a "column average plot", where the x-axis represents the horizontal distance through the selection and the y-axis the vertically averaged pixel intensity. To average horizontally, hold down the alt key. Use the Save or Copy buttons to save the profile data, formatted as a sequence of lines each containing a single number.

Surface Plot

Displays a three-dimensional graph of the intensities of pixels in a grayscale or pseudo color image. Creates a stack of plots when the source is a stack. Some plots can be improved by adjusting the contrast of the source image or smoothing it. When plotting a stack, closing the plot stack window will abort the plotting process.

[Example]

Change the Polygon Multiplier to adjust the number of profiles used to generate the plot. Check Draw Wireframe to have the outline each profile drawn in black. Check Shade to generate a shaded plot. The plot will be in color if the source image uses a color LUT. Check Draw Axis to have the three axis drawn and labeled. If Source Background is Lighter is checked, lighter areas in the source image represent lower elevations (valleys) while darker areas in the source image represent higher elevations (peaks). If Fill Plot Background with Black is checked, the plot is drawn with a black background.

The 3D Surface Plot plugin also generates surface plots. It works with all image types and you can interactively adjust viewing angle, perspective, scale, lighting and smoothing.

Gels Submenu

Use the commands in this submenu to analyze one-dimensional electrophoretic gels. These commands are similar to the Gel Plotting Macros distributed with NIH Image. Both use a simple graphical method that involves generating lane profile plots, drawing lines to enclose peaks of interest, and then measuring peak areas using the wand tool.

[Gel]

Here is what you need to do to analyse a 1-D gel:

  1. Use the rectangular selection tool to outline the first lane. This should be the left most lane if the lanes are vertical or the top lane if the lanes are horizontal. Note that lanes are assummed to be vertical unless the width of the initial selection is at least twice its height.
  2. Select Analyze>Gels>Select First Lane (or press "1") and "Lane 1 selected" will be displayed in the status bar. ImageJ will also duplicate the image and outline and label the lane if "Outline Lanes" is checked in the Analyze>Gels>Gel Analyzer Options.
  3. Move the rectangular selection right to the next lane (or down if the lanes are horizontal) and select Analyze>Gels>Select Next Lane (or press "2"). "Lane 2 selected" will be displayed in the status bar. ImageJ will also outline and label the lane if "Outline Lanes" is checked.
  4. Repeat the previous step for each remaining lane.
  5. Select Analyze>Gels>Plot Lanes (or press "3") to generate the lane profile plots.
  6. Use the straight line selection tool to draw base lines and/or drop lines so that each peak of interest defines a closed area. To get to all the lanes, it may be necessary to scroll the image vertically using the "Hand" tool. (Hold down the space bar to temporarily switch to this tool).
  7. For each peak, measure the size by clicking inside with the wand tool. If necessary, scroll the image by holding down the shift key and dragging.
  8. Select Analyze>Gels>Label Peaks to label each measured peak with its size as a percent of the total size of the measured peaks.
For practice, a sample gel is available in the File>Sample Images submenu. A tutorial is also available that shows how to use this procedure to analyze a dot blot.

Tools Submenu

This submenu provides access to various image analysis plugins.

Save XY Coordinates...

Writes to a text file the XY coordinates and pixel value of all non-background pixels in the active image. Background is assumed to be the value of the pixel at the upper left corner of the image. For grayscale images, writes three values per line (x, y, and value), separated by spaces. For RGB images, writes five values per line (x, y, red, green and blue). The origin of the coordinate system is at the lower left corner of the image.

Box Count...

Counts the number of boxes of an increasing size needed to cover a one pixel binary object boundary. The box size and the number of boxes necessary to cover the boundary are plotted on a log-log plot and the fractal dimension determined from the slope, i.e. D=-slope. For more information, see the "Fractal_Box_Counter.java" source file.

Analyze Line Graph

ImageJ can be used to recover numeric coordinate data from scanned line graphs using the following procedure. Steps 1-6 are not necessary for binary (black and white) graphs. For practice, use the File>Open Samples>Line Graph sample image.
  1. Open the image containing the graph.
  2. Open the thresolding tool (shift-t).
  3. Adjust the threshold so the graph is highlighted in red.
  4. Click on "Apply" (make sure foreground is black and background is white).
  5. Close the thresholding tool.
  6. Use the oval selection tool as an erasor (press backspace to erase) to isolate a single curve (note: background color must be white).
  7. Select the curve by clicking to the left of it with the wand tool.
  8. Use Edit/>Clear Outside to erase everything but the curve.
  9. Use Analyze>Tools>Analyze Line Graph get the XY coordinates.

ROI Manager

The ROI (Region of Interest) Manager is a tool for working with multiple selections. The selections can be from different locations on an image or from different slices of a stack. All selection types, including points and lines, are supported.

[ROI Manager]

Click Add to add the current selection to the list, or press "t", the keyboard shortcut for the Edit>Selection>Add to Manager command. The Roi manager creates a three part label. The first part (stacks only) is the slice number, the second part is the X coordinate of the selection, and the third part is the Y coordinate. Click on a label to restore the associated selection to the current image. With stacks, the selection is restored to the slice it came from. Click on Show All to display all the selections on the list. Hold down the shift key while clicking Add to "add and draw" and the alt key to "add and rename".

Install the ROIManagerMacros macro set and you will be able to add a selection by pressing the "1" key, add and name by pressing "2", add and draw by pressing "3", and add and advance to the next slice by pressing "4".

Update replaces the selected ROI on the list with the current selection. This is usually a modified version of a selection from the ROI Manager list.

Delete deletes the selected ROIs from the list. Deletes all the ROIs if none are selected.

Use Rename to rename the selected ROI.

Open opens a ".roi" file and adds it to the list or opens a ZIP archive (".zip" file) and adds all the selections contained in it to the list. Use the Open All macro to add all the ".roi" files in a folder.

Save saves the selected ROI as an ".roi" file. If no ROIs are selected, saves all the ROI Manager selections as a ZIP archive.

Measure measures the selected ROIs, or if none are selected, all ROIs on the list. With a stack, you will be given the option to measure all the slices if all ROIs are associated with the first slice (have labels like 0001-xxxx-yyyy) or all have labels in the form xxxx-yyyy. Use the Analyze>Set Measurements command to specify the measurement options.

Deselect deselects any selected ROIs on the list. Delete, Save, Measure, Draw, Fill, Label and Combine work with all ROIs on the list when none are selected.

Show All displays a non-destructive overlay on the current image that outlines and labels all ROI Manager selections. Click on a label (selection number) in the overlay to activate the corresponding selection on the ROI Manager list. Click again to erase the overlay.

More>> displays a drop down menu with six additional commands:

Draw draws outline of the selected ROIs using the current foreground color and line width. Outlines all selections on the list if none are selected. Click in the Image>Color>Color Picker window to change the foreground color. Use the Edit>Options>Line Width command to set the line width.

Fill fills the selected ROIs using the current foreground color. Fills all selections on the list if none are selected. Click in the Image>Color>Color Picker window to change the foreground color.

Label labels and outlines the selected ROIs using the current foreground color. Labels and outlines all selections on the list if none are selected. Unlike Show All, this changes the image contents.

Combine uses the union operator on the selected ROIs to create a composite selection. Combines all the ROIs if none are selected.

Split splits the current selection (it must be a composite selection) into its component parts and adds them to the ROI Manager.

Add Particles adds objects segmented by the particle analyzer to the ROI Manager. Requires that "Record Starts" be checked in the Analyze>Analyze Particles dialog box. Particle analyzer objects can also be added to the ROI Manager by checking "Add to Manager" in the Analyze Particles dialog box.

Sort sorts the list in alphanumeric order.

Help opens this page in the default browser.

Calibration Bar

Creates an RGB copy of the current image and displays a labeled calibration bar on it.

[dialog and bar]

Change Location to move the calibration bar. If there is a selection, the bar is initially drawn at the selection. Change Fill Color to adjust the bar's background color. Change Label Color to adjust the text color. Change Number of Labels to adjust the total number of values displayed. Change Decimal Places to adjust the number of decimal places present in the labels. Change Font Size to adjust the labels' font size. Change Zoom Factor to scale the entire calibration bar. If Bold Text is checked, labels are drawn bold.

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