[Solved] Convert PDF to bitmap using Ghostscript in cmd and read output pipe

[danielthoss]

Hi Forum,

I want to convert a PDF to a bitmap. I use the program Ghostscript to do this. Actually I let Ghostscript write a *.bmp-File and create a TBitmap from it. This works!!

But now I want to use the output pipe to read the bitmap without the detour over the *.bmp-File - maybe this way saves a lot of time because the files are bigger then 100MB.

I used this tutorial to do this: http://forum.codecall.net/topic/72472-execute-a-console-program-and-capture-its-output/

Question 1: In the tutorial he first wait for the end of the process and then reads the output pipe. If I'm doing this, the process never exit. But why?

Question 2: If I'm using just a small buffer size like 2048 it works, but if I increase it the image if broken and sometimes the process never exit. But why?

Have anyone an idea whats my mistake?


Start converting by a button press

Code: Pascal  [Select][+][-]

1. procedure TfrmPDF.Button1Click(Sender: TObject);
2. var
3.   MemStream: TMemoryStream;
4.   sGS, cmd: String;
5.   pic: TPicture;
6. begin
7.   self.timePreview:=GetTickCount();
8.   sGS      := pdfUtil.getFileTmp();
9.   cmd      := pdfUtil.getGhostCmdPipe(30, 1, 'C:\Users\thoss\Desktop\KAMA_8UP_final.pdf');
10.  
11.   logging.log('TEST', cmd);
12.  
13.   // Run Ghostscipt and read the bitmap from output pipe
14.   MemStream := TMemoryStream.Create;
15.   pdfUtil.RunCmdAsAnsiStringAndReadInMemStream(cmd, MemStream);
16.  
17.   // Create the bitmap from memory stream
18.   pic := TPicture.Create();
19.   pic.LoadFromStream(MemStream);
20.  
21.   // Show the image
22.   self.timePreview:=GetTickCount()-self.timePreview;
23.   self.Caption:= IntToStr(self.timePreview);
24.   imgOriginal.Picture := pic;
25.  
26.   FreeAndNil(MemStream);
27. end;    

Call ghostscript and read from output pipe

Code: Pascal  [Select][+][-]

1. function TFDFUtil.RunCmdAsAnsiStringAndReadInMemStream(cmd: AnsiString; memStream: TMemoryStream): DWORD ;
2. const
3.   ReadBufferCONST = 2048;
4. var
5.   security : TSecurityAttributes;
6.   readPipe, WritePipe : THandle;
7.   start : TStartUpInfo;
8.   processInfo : TProcessInformation;
9.   bytesRead, bytesReadTotal : DWord;
10.   apprunning, exitCode : DWord;
11.   i: Integer;
12. begin
13.   BytesRead := 0;
14.   bytesReadTotal := 0;
15.   Security.nlength := SizeOf(TSecurityAttributes);
16.   Security.binherithandle := true;
17.   Security.lpsecuritydescriptor := nil;
18.  
19.   // Create Pipes
20.   if Createpipe (ReadPipe, WritePipe, @Security, 0) then
21.   begin
22.     FillChar(Start,Sizeof(Start),#0);
23.  
24.     start.cb := SizeOf(start);
25.     start.hStdOutput := WritePipe;
26.     start.hStdInput := ReadPipe;
27.     start.dwFlags := STARTF_USESTDHANDLES + STARTF_USESHOWWINDOW;
28.     start.wShowWindow := SW_HIDE;
29.  
30.     // Create process
31.     if CreateProcess(nil, PChar(cmd), @Security, @Security, true, NORMAL_PRIORITY_CLASS, nil, nil, start, ProcessInfo) then
32.     begin
33.       repeat
34.         // make sure we have room
35.         MemStream.SetSize(bytesReadTotal + ReadBufferCONST);
36.  
37.         ReadFile(ReadPipe, (MemStream.Memory + bytesReadTotal)^, ReadBufferCONST, BytesRead, nil);
38.         bytesReadTotal := bytesReadTotal + BytesRead;
39.  
40.         if (BytesRead < ReadBufferCONST) then
41.         begin
42.           logging.log('RunCmdAsAnsiStringAndReadInMemStream', 'Readed in total: ' + IntToStr(bytesReadTotal + BytesRead));
43.           break;
44.         end;
45.  
46.         Apprunning := WaitForSingleObject(ProcessInfo.hProcess, 1);
47.       until (Apprunning <> WAIT_TIMEOUT);
48.  
49.       if (apprunning = WAIT_FAILED) then
50.       begin
51.         exitCode := GetLastError();
52.         logging.log('oFoilUtil | RunCmdAsAnsiString', 'System Error Codes: ' + IntToStr(exitCode));
53.       end;
54.     end;
55.  
56.     // Check return value
57.     GetExitCodeProcess(ProcessInfo.hProcess, &exitCode);
58.  
59.     if (exitCode <> 0) then
60.     begin
61.       ShowMessage('Error: ' + cmd + ' failed with ' + IntToStr(exitCode));
62.       logging.log('oFoilUtil | RunCmdAsAnsiString', 'Error: ' + cmd + ' failed with ' + IntToStr(exitCode));
63.     end;
64.  
65.     // Free everything
66.     CloseHandle(ProcessInfo.hProcess);
67.     CloseHandle(ProcessInfo.hThread);
68.     CloseHandle(ReadPipe);
69.     CloseHandle(WritePipe);
70.  
71.     result := exitCode;
72.  end;
73. end;    

[danielthoss]

I forgot to post the command to run ghostscript - if anyone whats to test the problem

cmd := C:\Program Files\gs\gs9.16\bin\gswin64c.exe -dUseCIEColor -dNumRenderingThreads=8 -sDEVICE=bmp16m -r30 -dNOPAUSE -dFirstPage=1 -dLastPage=1 -sOutputFile="C:\Temp\BMPTmp.bmp" "C:\Users\thoss\Desktop\ART1512326_HP30000.pdf" -c quit

[balazsszekely]

@danielthoss
1. Try TProcess with large output: http://wiki.freepascal.org/Executing_External_Programs#Reading_large_output
2. Before loading the picture, always set the position of the MemoryStream to 0

Code: Pascal  [Select][+][-]

1.   pic := TPicture.Create();
2.   MemStream.Position := 0;
3.   pic.LoadFromStream(MemStream);
4.  

3. You forget to free pic

PS: I did some tests, you won't gain much speed. Loading a 100Mb bmp from file into a MemoryStream is almost instantaneous, assigning the stream to a picture is the bottleneck:

Code: Pascal  [Select][+][-]

1.  MemStream := TMemoryStream.Create;
2.  try
3.    MemStream.LoadFromFile('C:\Temp\BMPTmp.bmp');
4.    MemStream.Position := 0;
5.    imgOriginal.Picture.LoadFromStream(MemStream); //<--this is the bottleneck
6.  finally
7.    MemStream.Free;
8.  end;

             
So keep it simple, let gswin64c.exe create the bmp, then load with a memorystream.

[danielthoss]

@GetMem

Thx for your hints and time!!

I changed the execution of Ghostscript to TProcess and now it works 

[balazsszekely]

@danielthoss

You're welcome!
Ok it works, but is it faster then loading directly from file?

[danielthoss]

@GetMem

Sorry for the long delay.

On my laptop it's not really faster - I think because of the build in SSD hard disk. On an old hard disk it whould be really faster and also if I increase the DPI value (GhostScript parameter -r) to 600 and higher to get a much better quality (resolution) of the image.