Interactive Histogram Chart
Several tools display their distribution in the same interactive chart. This page describes how to read it, how to navigate it, and how to evaluate a range of values with it. The tools that use it are listed under Where the Chart Appears.
The chart shows the distribution over the value range of the data. The horizontal axis carries the measured value, such as a gray value or a wall thickness, and the vertical axis carries how often that value occurs.
Reading the Chart
| Element | Description |
|---|---|
| Horizontal axis | The measured value. Its title is shown in the lower right corner of the plot. |
| Vertical axis | How often each value occurs. Its title is shown along the left edge of the plot. |
| Chart title | Shown in the upper right corner of the plot. |
| Grid | Lines at the labelled divisions, with fainter lines at the divisions between them. |
| Value readout | While the pointer is over the plot, a crosshair marks the nearest bin and a box reports its value and frequency. |
The chart follows the application theme. It is drawn on a light background under a light theme and on a dark background under a dark theme.
Navigating
Zooming
| Action | Result |
|---|---|
| Mouse wheel over the horizontal ruler | Zooms the horizontal axis around the pointer |
| Mouse wheel over the vertical ruler | Zooms the vertical axis |
| Ctrl + mouse wheel in the plot | Zooms the horizontal axis around the pointer |
| Ctrl + Shift + mouse wheel in the plot | Zooms the vertical axis |
| Ctrl + drag in the plot | Zooms into the dragged value range |
| Double click in the plot | Fits the whole distribution back into the chart |
The mouse wheel needs a modifier over the plot area. The chart is placed in panels that scroll, and taking the plain wheel would stop the panel from scrolling while the pointer rests on the chart.
The horizontal axis never reaches past the measured values, so zooming out stops once the whole distribution is shown. The vertical axis reaches half of the fitted range above the highest bar, so a peak does not have to touch the top of the plot.
Scrolling
| Action | Result |
|---|---|
| Drag the horizontal ruler | Scrolls the horizontal axis |
| Drag the vertical ruler | Scrolls the vertical axis |
| Drag with the middle mouse button | Scrolls both axes |
| Shift + mouse wheel in the plot | Scrolls the horizontal axis |
A ruler scrolls only while the chart shows less than the range it can reach. The pointer shows the scroll cursor over a ruler that can be scrolled, and the normal cursor over one that cannot.
Keyboard
The chart accepts these keys once it has the keyboard focus, which it takes when you move to it with Tab. Clicking the chart does not move the focus away from the control you were editing.
| Key | Result |
|---|---|
| + / - | Zooms both axes in or out |
| Arrow keys | Scrolls the axes |
| Home | Fits the whole distribution back into the chart |
| Delete | Removes the selected interval |
| Ctrl+C | Copies the chart to the clipboard |
Intervals
An interval marks a range of values and reports what the distribution contains inside it.
Working with Intervals
| Action | Result |
|---|---|
| Drag across the plot | Creates an interval over the dragged range |
| Drag an interval border | Moves that border |
| Drag the body of an interval | Moves the whole interval, keeping its width |
| Click an interval | Selects it |
| Click outside every interval | Clears the selection |
The context menu offers Create Interval, Remove Interval, and Remove All Intervals. Several intervals can exist at once. The selected one is drawn with solid borders and reports its values.
Reported Values
The selected interval reports the following next to it:
| Value | Description |
|---|---|
| Left | The left border of the interval |
| Right | The right border of the interval |
| Mean | The average measured value inside the interval, weighted by how often each value occurs |
| Dev | The standard deviation of the measured values inside the interval |
| Sum | The total frequency inside the interval, expressed as a percentage under relative normalization |
| Percentage | The share of the whole distribution that falls inside the interval |
Bins are counted when their value lies within the borders, both borders included.
Mean and Dev describe the measured values, so they do not change when you switch the normalization or the scaling of the frequency axis. Both settings change only how the distribution is drawn. They do change with the binning, because the binning changes which bins exist. Percentage stays the same under either normalization.
Threshold Lines
Some tools draw the borders of a value range they work with as lines on the distribution, so the range can be set where the values themselves are. Where they appear is listed under Where the Chart Appears. These tools show the range instead of intervals, so a drag on the background of the chart moves the displayed range rather than creating an interval.
| Action | Result |
|---|---|
| Drag a line | Moves that border |
| Drag the shaded area between two lines | Moves the whole range, keeping its width |
The borders cannot cross each other, and the range stops as a whole at the ends of the value range. The tool that owns the chart also offers input boxes for entering an exact value.
A tool whose range is described by a middle and a width, such as Window/Level, draws the two lines as a mirrored pair instead:
| Action | Result |
|---|---|
| Drag a line | Moves both borders apart or together, keeping the middle where it is |
| Drag the shaded area between them | Moves the middle, keeping the width |
The pair stops when either border reaches the end of the value range, and neither border passes the middle.
Display Options
Right-click the chart to open its context menu. The settings are kept with the tool and restored the next time it is opened.
The available options depend on the tool. Histogram, Volume Statistics, Mask Statistics, Surface Statistics, and Void/Inclusion Analysis report counts and therefore do not offer normalization; the mesh quality tools offer both absolute and relative normalization. Wall Thickness, Deviation, Curvature, Extrema, and Gray Value Analysis provide their own absolute, relative, and cumulative surface modes above the chart, so the chart does not offer a second normalization or binning control for these tools.
Graph
| Option | Description |
|---|---|
| Bars | One bar per bin |
| Line | The outline of the distribution |
| Filled Line | The outline with the area below it filled |
Color
| Option | Description |
|---|---|
| Solid | The distribution uses one color |
| From Color Bar | The distribution is colored by its position in the color bar of the tool |
Normalization
| Option | Description |
|---|---|
| Absolute | Frequencies are shown as they were measured |
| Relative | Frequencies are shown as a percentage of the whole distribution |
Under relative normalization the vertical axis labels carry a percent sign.
Binning
Binning groups the bins of the distribution before it is drawn. It changes the chart and the reported interval values, and never the measured data.
| Option | Description |
|---|---|
| Off | The bins are shown as they were measured |
| From Color Bar | One bin per section of the color bar. Offered only by a color bar that is divided into sections. |
| Bin Count | A chosen number of equally wide bins |
| Bin Width | Equally wide bins of a chosen width |
A tool that offers its own bin count does not repeat it here, because the two would describe different things. See the page of the tool for which one applies.
Scale
| Option | Description |
|---|---|
| Linear | An evenly divided frequency axis |
| Logarithmic | A frequency axis that brings out the rare values next to a dominant peak |
Grid
| Option | Description |
|---|---|
| Show X Grid | Vertical grid lines |
| Show Y Grid | Horizontal grid lines |
| Show Value Readout | The crosshair and the value box that follow the pointer |
Zoom
Zoom In, Zoom Out, and Reset Zoom are also available from the context menu.
Exporting the Chart
| Action | Result |
|---|---|
| Export as CSV... | Writes the distribution as value and frequency data |
| Copy to Clipboard | Copies a picture of the chart |
| Save as Image... | Saves a picture of the chart as PNG, JPG, or BMP |
Both picture exports use printable colors on a white background, so the result stays readable in a document regardless of the theme the chart is displayed with.
The CSV is written in one of two forms, depending on the data:
- Where a row stands for a value that was measured in its own right, it carries that value and its frequency. This applies to data measured over whole numbers, such as the gray values of an integer image, which are written as whole numbers.
- Otherwise a row counts every value within a range rather than at a single value, and states that range in a from and a to column, followed by the frequency, so a count is never read as measured at one exact value. This applies to the bars the chart draws, and to data that has no value step of its own, such as the gray values of a floating point image.
If a tool that measures at full resolution cannot prepare the distribution, for example because the object it was measured on is no longer active, the export is cancelled with a message. The bins drawn on screen are not written in its place.
The tools listed under Threshold Lines draw the distribution only as a preview for setting a range, not as measurement data, so their chart does not offer Export as CSV.... Copying the chart and saving it as an image stay available.
Where the Chart Appears
| Tool | Distribution |
|---|---|
| Histogram | Gray values of the active volume |
| Volume Statistics | Gray values of the active volume, next to the statistics tables |
| Mesh Quality Analyzer | The selected quality metric over the triangles or the elements of a mesh |
| Mask Statistics | The selected metric over the labels or the connected regions of a mask |
| Surface Statistics | The selected metric over the connected regions of a surface mesh |
| Void/Inclusion Analysis | The selected metric over the detected defects |
| Wall Thickness Analysis | Wall thickness over the analyzed surface |
| Deviation Analysis | Deviation between the analyzed and reference objects |
| Curvature Analysis | Curvature over the analyzed surface |
| Extrema Analysis | Projected distance over the analyzed surface |
| Gray Value Analysis | Gray values sampled over the analyzed surface |
The following tools also draw their value range as threshold lines on the distribution:
| Tool | Range |
|---|---|
| Window/Level | Gray value interval the slice views display |
| Threshold | Gray values included in the mask |
| Surface Determination | The isovalue, drawn as a single line |
| LiveWire, GrowCut, Dynamic Region Grow | Gray values the segmentation is restricted to |
| Edit Mask | Gray values a painted region is restricted to |
Related Tools
| Page | Description |
|---|---|
| Histogram | Histogram of the gray values of a volume |
| Volume Statistics | Grayscale statistics and histogram of a volume |
| Mesh Quality Analyzer | Quality metrics of a surface or volume mesh |
| Draw Profile Line | Intensity along a user defined line |