# How to extract the images from a wolfram list to an array/list of byte arrays using JLink in Java

I have the following code in Java, where I am trying to use the WolframAlpha command and get the result as a list of images (byte arrays)

String expr = "WolframAlpha[\"solve x^2+2x+1=0\", \"PodImages\", IncludePods->\"Result\", PodStates->\"Step-by-step solution\"]"


Evaluating the expression in a terminal gives me something like this. Using the Export function, I've seen the 2 images and they look right.

In[6]:= WolframAlpha["solve x^2+2x+1=0","PodImages", IncludePods->"Result", PodStates->"Step-by-step solution"]

Out[6]= {-Image-, -Image-}



I've tried to get the result as a byte[][] (mathLink.getByteArray2()), but I get the MLGet out of sequence exception, so I assumed the result I got wasn't an array of byte arrays.

I also tried getting the result as an Object, but I got the error that Expression on link is not a valid Java object reference

Doing mathLink.getType() told me that the result that I'm getting is a MTFUNCTION, so I tried reading the result as a function. Investigating further, I found out that the function type was List with 2 arguments. I'm assuming that those 2 arguments are the 2 images I want to get.

So my question is: How can I extract the images from the result as an array or list in Java?

Sorry if this is a silly question - I'm new to using JLink and the Wolfram Language

EDIT

In case this helps anyone, I tried logging the output from mathLink.getExpr().toString() and got:

{
Image[
NumericArray[
{{
{255, 255, 255}, {255, 255, 255}, ...more of these
}},
"UnsignedInteger8"
],
"Byte",
Rule[ColorSpace, "RGB"],
Rule[ImageSize, Automatic],
Rule[Interleaving, True],
Rule[Magnification, 1]
],
Image[
...more of the same as above
]


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• I can't check it right now, but you're getting image object, not array of bytes from Mathematica (btw providing the full code you use could help) as a result of evaluate. To extract image data you can use ImageData (and in case of list of images — Map over it), something like: Nov 27 '21 at 12:09
• 2: (this will give you a list of two arrays:  WolframAlpha["solve x^2+2x+1=0", "PodImages", IncludePods -> "Result", PodStates -> "Step-by-step solution"] // Map[ImageData[#, Byte, Interleaving -> True] &] // Map[Dimensions]  basically what math link tells you're trying to read expression (which is not an array) as an array Nov 27 '21 at 12:19