The JFreeChart nodes are not installed by default, but the extension is available from the standard KNIME update site under the name KNIME JFreeChart.
The common part of these nodes is that you have to specify the appearance of the result in advance, and the focus is not on the view, but on the resulting image port object.
In the General Plot Options Configuration tab, you can specify the type of the resulting image (PNG or SVG), the size, the title, colors, and the font size (relative to the standard font for each item printed).
You can use the port objects in the reports, but you can also use them to check certain properties if you iterate through a loop and convert the result with Image To Table.
It is important to note that the customizable JFreeChart View tab is only available in freshly executed nodes. The generated image can be visualized either using the view or the image output.
In the JFreeChart View tab, you can customize (from the context menu) almost every aspect of the diagram (fonts, colors, tics, ranges, orientation, and outline style). This way, the output can be of quite a high quality. It is also important to note that the export is easier: you can use the Copy option to copy it to the clipboard or directly use the Save as... option to save it as a PNG file, and because there are no visible controls, you do not have to cut them off.
These nodes do not support HiLiting, but they provide tooltips about values. The support for properties is usually not implemented.
You can zoom in on these nodes by selecting a region (left to right, top to bottom) and zoom out by selecting in the opposite direction. You can also use the context menu's zooming options. (It seems that you cannot move around using the mouse or keyboard, so you have to zoom out and select another region if you want to see the details of that region.)
The Bar Chart (JFreeChart) node's view is similar to a usual histogram, but it does not allow any other aggregation other than the count function, and only nominal columns are accepted. The color of the first column can be specified, just like the labels for the axis. The nominal columns' values can be rotated, and the angle can be set. You can also enable/disable the legends.
The GroupBy Bar Chart (JFreeChart) node's configuration is similar, except in this case, the nominal column is a single column (it can also be numeric), and the rest of the numeric columns can be visualized against it. It is important to note that the binning column should contain unique values. (The numeric values are grouped by these values.)
The Bubble Chart (JFreeChart) node's view is analogous to the Scatter Plot view, but in this case, you cannot set the color and the shape, but the color is not opaque. It also cannot handle nominal columns, so you have to convert them to numbers if you want to plot them against other columns. You must specify the x and y positions of the bubbles, just like their radius.
The Heatmap (JFreeChart) node is capable of visualizing not just the values in multiple columns, but also the distances from the other color-coded rows, when a distance column is available.
The extreme colors can be specified in the HeatMap (JFreeChart) node's configuration for the minimal and the maximal distance, and the legend can also be visible or hidden. The labels for the axes can be specified, and the tooltip is also available on demand.
This is a bit different from the histogram views previously introduced. In this view, the histograms can be either behind or in front of other histograms. The different ranges are shown on the same scale, so some of them can be wider while the others are narrower.
The color of the bars is only adjustable for the first column. The histograms are plotted in order, the last is at the back, while the first is in the front. You cannot change the order of the histograms from the view of Histogram (JFreeChart).
The Interval Chart (JFreeChart) node's view is not so interesting when your label is not unique (or the order is not defined by its alphabetical order). But this view supports the time values without the need to transform your data with time information before visualization, focusing on that information.
You can specify the grouping nominal column (Label) and the start and end positions of the time intervals. Each row represents an interval.
It supports the color properties, so you can create overlapping intervals with different colors.
The Line Chart (JFreeChart) node's view is quite similar to the regular Line Plot view, except in this case, you cannot have dots to show the values. However, there is an extra input table to specify the colors of the series.
The other difference is that when specified, you can use the numeric or date column's values instead of the rows for the values of other columns; however, the connections are still done by the adjacent rows.
The Pie Chart (JFreeChart) node's view is similar to the Pie Chart node, but it is less interactive. It still uses the color properties (as opposed to the other JFreeChart nodes) and can draw the pie in 3D.
The Scatter Plot (JFreeChart) node uses the shape and color properties, so it can visualize at most four columns. This is still quite static but configurable, and the result looks good (it can contain the legend, so it is practically ready to paste).
This node is quite constant too; you have to decide which columns should be there in the configuration dialog.