Upload images to Imgur from Mathematica

A little bird just informed me of a Mathematica solution to this question (the underlying implementation still uses JLink, but this answer hides all the java related code):

imgur[expr_] := Module[
 {url, key, image, data, xml, imgurUrl},
 url = "http://api.imgur.com/2/upload";
 key = "c07bc3fb59ef878d5e23a0c4972fbb29";
 image = Fold[ExportString, expr, {"PNG", "Base64"}];
 xml = Import[url, 
  "XML", "RequestMethod" -> "POST", 
  "RequestParameters" -> {"key" -> key, "image" -> image}];
 imgurUrl = Cases[xml, XMLElement["original", {}, {string_}] :> string, 
  Infinity][[1]];
 "![Mathematica graphic](" <> imgurUrl <> ")"
]

This is V8 only and the XML import options "RequestMethod" and "RequestParameters" are undocumented and experimental (and therefore subject to change).


Note: This is using the anonymous imgur uploader with my anonymous key. The imgur site restricts uploads to 50 uploads/hour which should be fine normally, but this may cause a problem if a lot of people try this simultaneously. So please get your own anonymous key here:

http://imgur.com/register/api_anon

And then replace the key in the code below with your own key (thanks!).

The trickiest part to code was the conversion from a Mathematica expression to PNG image to Base64 encoding to URL encoding. There are about a 1,000 ways to do it wrong and I think I managed to try them all.

The code breaks down into a few pieces:

  • Construct the POST url
  • Make the HTTP connection
  • Send the POST url
  • Read back the result, which is XML
  • Extract the imgur url from the XML
  • Format the imgur url as markdown (or as a Mathematica Hyperlink function).

Here is the code:

imgur[expr_] :=
 Module[{url, key, image, data, jUrl, jConn, jWriter, jInput, buffer,
   byte, xml, imgurUrl},
  Needs["JLink`"];
  JLink`JavaBlock[
   JLink`LoadJavaClass["java.net.URLEncoder"];
   url = "http://api.imgur.com/2/upload";
   key = "c07bc3fb59ef878d5e23a0c4972fbb29";
   image = ExportString[ExportString[expr, "PNG"], "Base64"];
   data =
    URLEncoder`encode["key"   , "UTF-8"] <> "=" <>
    URLEncoder`encode[ key    , "UTF-8"] <> "&" <>
    URLEncoder`encode["image" , "UTF-8"] <> "=" <>
    URLEncoder`encode[ image  , "UTF-8"] ;
   jUrl = JLink`JavaNew["java.net.URL", url];
   jConn = jUrl@openConnection[];
   jConn@setDoOutput[True];
   jWriter =
    JLink`JavaNew["java.io.OutputStreamWriter",
     jConn@getOutputStream[]];
   jWriter@write[data];
   jWriter@flush[];
   jInput = jConn@getInputStream[];
   buffer = {};
   While[(byte = jInput@read[]; byte >= 0), AppendTo[buffer, byte]];
   ];
  xml = ImportString[FromCharacterCode[buffer], "XML"];
  imgurUrl =
   Cases[xml,
     XMLElement["original", {}, {string_}] :>
      string, \[Infinity]][[1]];
  "![Mathematica graphic](" <> imgurUrl <> ")"
  ]

Testing:

In[]:= g = Graphics[{Blue, Disk[]}, PlotRange -> 1.2, ImageSize -> Small];
       pic = Overlay[{Blur[Binarize@g, 10], g}];
       imgur[pic]

Out[]= ![Mathematica graphic](http://i.imgur.com/eGOlL.png)

And the actual image:

Mathematica graphic


Note: Get an ready-made palette with this functionality here.

Arnoud's solution got me excited and impatient, so here's an improvement to it. I couldn't have done this without studying his code. This version seems to be somewhat more reliable and less prone to timeout errors, but to be honest, I know no Java at all, so any improvements are welcome.

Most importantly: this version uploads to stack.imgur.com directly, so it's safe to use here on StackOverflow, without having to worry that uploaded images will disappear after a while.

I provide three functions:

  • stackImage uploads the expression, exported as PNG, and returns the URL
  • stackMarkdown returns the markdown, ready to be copied
  • stackCopyMarkdown copies the markdown to the clipboard

Next step: create a palette button that does this automatically for the selected graphic in the notebook. Improvements to the code are very welcome.

Needs["JLink`"]


stackImage::httperr = "Server returned respose code: `1`";
stackImage::err = "Server returner error: `1`";

stackImage[g_] :=
 Module[
  {getVal, url, client, method, data, partSource, part, entity, code, 
   response, error, result},

  (* this function attempts to parse the response fro the SO server *)
  getVal[res_, key_String] :=
   With[{k = "var " <> key <> " = "},
    StringTrim[
     First@StringCases[First@Select[res, StringMatchQ[#, k ~~ ___] &], 
       k ~~ v___ ~~ ";" :> v],
     "'"]
    ];

  data = ExportString[g, "PNG"];

  JavaBlock[
    url = "https://stackoverflow.com/upload/image";
    client = JavaNew["org.apache.commons.httpclient.HttpClient"];
    method = JavaNew["org.apache.commons.httpclient.methods.PostMethod", url];
    partSource = JavaNew["org.apache.commons.httpclient.methods.multipart.ByteArrayPartSource", "mmagraphics.png", MakeJavaObject[data]@toCharArray[]];
    part = JavaNew["org.apache.commons.httpclient.methods.multipart.FilePart", "name", partSource];
    part@setContentType["image/png"];
    entity = JavaNew["org.apache.commons.httpclient.methods.multipart.MultipartRequestEntity", {part}, method@getParams[]];
    method@setRequestEntity[entity];
    code = client@executeMethod[method];
    response = method@getResponseBodyAsString[];
  ]

  If[code =!= 200, Message[stackImage::httperr, code]; Return[$Failed]];
  response = StringTrim /@ StringSplit[response, "\n"];

  error = getVal[response, "error"];
  result = getVal[response, "result"];
  If[StringMatchQ[result, "http*"],
   result,
   Message[stackImage::err, error]; $Failed]
  ]


stackMarkdown[g_] := "![Mathematica graphics](" <> stackImage[g] <> ")"


stackCopyMarkdown[g_] := Module[{nb, markdown},
  markdown = Check[stackMarkdown[g], $Failed];
  If[markdown =!= $Failed,
   nb = NotebookCreate[Visible -> False];
   NotebookWrite[nb, Cell[markdown, "Text"]];
   SelectionMove[nb, All, Notebook];
   FrontEndTokenExecute[nb, "Copy"];
   NotebookClose[nb];
   ]
  ]

Update:

Here's a button that will show a preview of the selection and will offer uploading (or cancelling). It requires the previous functions to be defined.

Button["Upload to SO",
 Module[{cell = NotebookRead@InputNotebook[], img},
  If[cell =!= {}, img = Rasterize[cell];
   MessageDialog[
    Column[{"Upload image to StackExchange sites?", 
      img}], {"Upload and copy MarkDown" :> stackCopyMarkdown[img], 
     "Cancel" :> Null}, WindowTitle -> "Upload to StackExchange"]]]]

Unfortunately I can't put the button in a palette (CreatePalette) because the palette dimensions will influence the rasterization. Solutions to this problem are welcome.

Update 2:

Based on the answer to this question, here's a working Windows-only palette button:

button = Button["Upload to SO",
  Module[{sel},
   FrontEndExecute[
    FrontEndToken[FrontEnd`SelectedNotebook[], "CopySpecial", "MGF"]];
   sel = Cases[NotebookGet@ClipboardNotebook[], 
     RasterBox[data_, ___] :> 
      Image[data, "Byte", ColorSpace -> "RGB", Magnification -> 1], 
     Infinity];
   If[sel =!= {},
    With[{img = First[sel]},
     MessageDialog[
      Column[{"Upload image to StackExchange sites?", 
        img}], {"Upload and copy MarkDown" :> stackCopyMarkdown[img], 
       "Cancel" :> Null}, WindowTitle -> "Upload to StackExchange"]
     ]
    ]
   ]
  ]

CreatePalette[button]

Warning: it destroys the clipboard contents even if you click cancel in the preview box.

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