Skip to main content

graphics - Encoding format used by GraphicsData?


I am trying to extract some graphics stored in PICT format from a Mathematica notebook, using a platform that doesn't support PICT. If I look at the .nb file in a plain text editor, or if I use FullForm, then I can see that the picture is stored as a GraphicsData head with a text string encoding the picture. It doesn't appear that the GraphicsData head uses Base64 or any other binary-to-text encoding that I know of off the top of my head, but I would like to be able to copy-and-paste the GraphicsData string and decode it manually. Is this possible? Does GraphicsData use a well-known encoding scheme?



Answer



I found an example on the web. Here is code that will convert the PICT data from the format stored in the notebook file into a .pict file that can be opened by an image viewer (e.g. Photoshop).



DecodePICT[data_String] := Module[
    {slash, backslash, zero, LF, CR, decode, codes, len, i},
    {slash, backslash, zero, LF, CR} = ToCharacterCode["/\\0\n\r"];
    decode[char_] := If[char == slash, backslash-zero, char-zero];
    len = Length[codes = ToCharacterCode[data]];
    i = 1;
    Join[Table[0,{512}], Last@Last@Reap@While[i <= len-1,
        Which[
            codes[[i]] == LF || codes[[i]] == CR,
            i++,

            codes[[i]] == backslash,
            i += 4,
            True,
            Sow@BitAnd[BitOr[
                BitShiftLeft[decode[codes[[i]]], 2],
                BitShiftRight[decode[codes[[i+1]]], 4]
            ], 255];
            i++;
            If[i <= len-1,
                Sow@BitAnd[BitOr[

                    BitShiftLeft[decode[codes[[i]]], 4],
                    BitShiftRight[decode[codes[[i+1]]], 2]
                ], 255]
            ];
            i++;
            If[i <= len-1,
                Sow@BitAnd[BitOr[
                    BitShiftLeft[decode[codes[[i]]], 6],
                    BitShiftRight[decode[codes[[i+1]]], 0]
                ], 255]

            ];
            i += 2;
        ]
    ]]
];

str = "0N801`0]05815@0A0_l<0?ooool0;@0000L0004E0000DP000000002Q0O@0hd=U
  K6aK8U`lG0eSKgEbHVEKM5mM83Xm80eLM51QLV5]IGAbJF=@K6md  :b1d84=_Le]fGBU3Kg=K  DfU^FgIMOBakMR`P<2`P
  NVD]?W/b  3B0PBFeQIfEBIFMYKfh]?W]k<2`P  00L0;@1B0AD0<@0602d0DP9203401`920582@P0J0000000002`01@R^0Te30003
  2:h0104000d0300^00@0o`0002/]4PiSKgEbHVEKM5mM83Xm8000:b0?4U1QLV5]
  IGAbJF=@K6md  M213Kg=KMUdYDfU^Fc9fGB`002X?6G@PDfU^FgIMOBakMR`P<2`P  0?l";

Export["~/Desktop/foo.pict", DecodePICT[str], "Binary"]

Comments

Post a Comment

Popular posts from this blog

mathematical optimization - Minimizing using indices, error: Part::pkspec1: The expression cannot be used as a part specification

I want to use Minimize where the variables to minimize are indices pointing into an array. Here a MWE that hopefully shows what my problem is. vars = u@# & /@ Range[3]; cons = Flatten@ { Table[(u[j] != #) & /@ vars[[j + 1 ;; -1]], {j, 1, 3 - 1}], 1 vec1 = {1, 2, 3}; vec2 = {1, 2, 3}; Minimize[{Total@((vec1[[#]] - vec2[[u[#]]])^2 & /@ Range[1, 3]), cons}, vars, Integers] The error I get: Part::pkspec1: The expression u[1] cannot be used as a part specification. >> Answer Ok, it seems that one can get around Mathematica trying to evaluate vec2[[u[1]]] too early by using the function Indexed[vec2,u[1]] . The working MWE would then look like the following: vars = u@# & /@ Range[3]; cons = Flatten@{ Table[(u[j] != #) & /@ vars[[j + 1 ;; -1]], {j, 1, 3 - 1}], 1 vec1 = {1, 2, 3}; vec2 = {1, 2, 3}; NMinimize[ {Total@((vec1[[#]] - Indexed[vec2, u[#]])^2 & /@ R...
Post a Comment
Read more

functions - Get leading series expansion term?

Given a function f[x] , I would like to have a function leadingSeries that returns just the leading term in the series around x=0 . For example: leadingSeries[(1/x + 2)/(4 + 1/x^2 + x)] x and leadingSeries[(1/x + 2 + (1 - 1/x^3)/4)/(4 + x)] -(1/(16 x^3)) Is there such a function in Mathematica? Or maybe one can implement it efficiently? EDIT I finally went with the following implementation, based on Carl Woll 's answer: lds[ex_,x_]:=( (ex/.x->(x+O[x]^2))/.SeriesData[U_,Z_,L_List,Mi_,Ma_,De_]:>SeriesData[U,Z,{L[[1]]},Mi,Mi+1,De]//Quiet//Normal) The advantage is, that this one also properly works with functions whose leading term is a constant: lds[Exp[x],x] 1 Answer Update 1 Updated to eliminate SeriesData and to not return additional terms Perhaps you could use: leadingSeries[expr_, x_] := Normal[expr /. x->(x+O[x]^2) /. a_List :> Take[a, 1]] Then for your examples: leadingSeries[(1/x + 2)/(4 + 1/x^2 + x), x] leadingSeries[Exp[x], x] leadingSeries[(1/x + 2 + (1 - 1/x...
Post a Comment
Read more

What is and isn't a valid variable specification for Manipulate?

I have an expression whose terms have arguments (representing subscripts), like this: myExpr = A[0] + V[1,T] I would like to put it inside a Manipulate to see its value as I move around the parameters. (The goal is eventually to plot it wrt one of the variables inside.) However, Mathematica complains when I set V[1,T] as a manipulated variable: Manipulate[Evaluate[myExpr], {A[0], 0, 1}, {V[1, T], 0, 1}] (*Manipulate::vsform: Manipulate argument {V[1,T],0,1} does not have the correct form for a variable specification. >> *) As a workaround, if I get rid of the symbol T inside the argument, it works fine: Manipulate[ Evaluate[myExpr /. T -> 15], {A[0], 0, 1}, {V[1, 15], 0, 1}] Why this behavior? Can anyone point me to the documentation that says what counts as a valid variable? And is there a way to get Manpiulate to accept an expression with a symbolic argument as a variable? Investigations I've done so far: I tried using variableQ from this answer , but it says V[1...
Post a Comment
Read more