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--- documents:120206pyip_cooking:python_imagej_cookbook [2025/10/05 20:45] – [Plugin: Ridge Detection] kota
+++ documents:120206pyip_cooking:python_imagej_cookbook [2025/10/05 22:53] (current) – [Converting Java array types] kota
@@ Line 751: / Line 751: @@
 To initialize a Java native 2D array (e.g. float[][]), create a Python 2D array first, then convert it to a Java 2D array using jarray. See the example code below.
-<code>
+<code python>
 import jarray
 import java.lang.Class
@@ Line 776: / Line 776: @@
 </code>
 "java.lang.Class.forName("[F")" is the reflection, and the name of the Java native float class is "[F".
+==== Creating floating point processor image ====
+Java float 2D array can also be made using jarray.zeros (like numpy.zeros).
+Here is an example of creating a floating-point image from 2D array.
+<code python linenums:1>
+from jarray import zeros
+from ij import ImagePlus
+from ij.process import FloatProcessor
+#generate 200 x 100 floating point matrix
+matrix2D = [zeros(100, 'f')]*200
+# check the generated matrix
+print(matrix2D)
+#[array('f', [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0 ...
+rows = len(matrix2D)
+cols = len(matrix2D[0])
+print("rows {} cols {}".format(rows, cols))
+#rows 200 cols 100
+# instantiate FP image
+fp = FloatProcessor(matrix2D)
+#check created FP image
+print("image width {} height {}".format(fp.getWidth(), fp.getHeight()))
+ImagePlus('fp', fp).show()
+</code>
+In short, as simple as:
+<code python linenums:1>
+from jarray import zeros
+from ij import ImagePlus
+from ij.process import FloatProcessor
+matrix2D = [zeros(100, 'f')]*200
+ImagePlus('fp', FloatProcessor(matrix2D)).show()
+</code>
 ==== Converting Java array types ====
-Sometimes we need to convert the type of Java array e.g. double[] to int[]. For this, there is no magic trick and need to run a loop. Below is a code fragment.
+Sometimes we need to convert the type of Java array e.g. double[] to int[]. In Java we can do this by a for-loop with casting from float to int, but in Jython we can use the map function.
 <code:py>
+from ij import IJ
 from ij.process import StackStatistics
 import jarray
+imp = IJ.getImage() #stack
 stackstats = StackStatistics(imp)
-histD = stackstats.histogram()
+histD = stackstats.histogram() #double[] returned, taken as floats in python
-hist = jarray.zeros(len(histD), 'i')
+print(type(histD[0]))
-for i in range(len(histD)):
-    hist[i] = int(histD[i])
+hist = map(int, histD)
+histInt = jarray.array(hist, 'i')
+print(type(histInt[0])) #Java int[]
 </code>
@@ Line 2675: / Line 2721: @@
 rm.runCommand(imp, 'Show All')
-<\code>
+</code>