JPEG properties

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5 total messages Started by Colin B Maharaj Mon, 09 Aug 2004 11:28

#437

Author: Colin B Maharaj
Date: Mon, 09 Aug 2004 11:28

43 lines
2612 bytes

Hi all, is there anyway to get the dimensions of a jpeg without opening 
it and loading it into a Bitmap memory block. The code snippet here 
creates a wrapper for jpegs whose file names are in a string list, if I 
have 30 jpegs does it mean I load all these jpegs one by one? Is there a 
way I can read the header and get the dimensions? This way I do not take 
  up much resources?

  AnsiString MakeJPEGHtmlWrapper(TStringList * L)
  {
    AnsiString A = "<html>\r\n<head>\r\n</head><body><br>\r\n";
    A += "<";
    A += "table style=\"width: 100%; text-align: left;\"";
    A += "border=\"0\"";
    A += "cellpadding=\"2\"";
    A += "cellspacing=\"2\"";
    A += "<tbody>";
    TJPEGImage *jpg = new TJPEGImage;
    Graphics::TBitmap *bmp = new Graphics::TBitmap;
    for (int i=0; i<L->Count; i++)
    {
      AnsiString B = L->Strings[i];
      while (B.Length() && B.Pos("\\")>0) B.Delete(1, 1);
      if (FileExists(B)==true)
      {
         A += "\r\n<tr>\r\n";
         A += "  <td style=\"vertical-align: top;\"><img title=\"";
         A += (AnsiString) "Image " + IntToStr(i+1) + "\"";
         A += (AnsiString) "src=\"";
         A += B; A += "\"";
         A += (AnsiString) " alt=\"\" ";
         A += (AnsiString) " style=\"";
         jpg->LoadFromFile(B); // does this take up much resources??
         bmp->Assign(jpg);
         A += (AnsiString) "width: " + IntToStr(bmp->Width)+"px\; " +
                           "height: " + IntToStr(bmp->Height)+"px\; \">";
         A += " </td>\r\n </tr>\r\n ";
      }
    }
    A += " </tbody>\r\n </table>\r\n ";
    A += " </body>\r\n </html>\r\n ";
    delete jpg;
    return A;
  }

Re: JPEG properties

#438

Author: Remy Lebeau (TeamB)
Date: Mon, 09 Aug 2004 16:56

35 lines
1868 bytes

"Colin B Maharaj" <noreply@myhost.com> wrote in message
news:41175fe0@newsgroups.borland.com...

> Hi all, is there anyway to get the dimensions of a jpeg
> without opening it and loading it into a Bitmap memory block.

TJPEGImage inherits Width and Height properties from TGraphic.  You don't
need to convert to TBitmap first:

    AnsiString MakeJPEGHtmlWrapper(TStringList * L)
    {
        //...
        TJPEGImage *jpg = new TJPEGImage;
        //...
        jpg->LoadFromFile(B);
        //..
        A += ( "width: " + IntToStr(jpg->Width) + "px; height: " +
IntToStr(jpg->Height) + "px; \">" );
        //...
        delete jpg;
        //...
    }

> The code snippet here creates a wrapper for jpegs whose
> file names are in a string list, if I have 30 jpegs does it mean
> I load all these jpegs one by one?

Yes.

> Is there a way I can read the header and get the dimensions?

Not unless you open the files yourself and decode the jpeg data manually.


Gambit

Re: JPEG properties

#439

Author: Colin B Maharaj
Date: Tue, 10 Aug 2004 02:56

28 lines
1822 bytes

Thanks Remy for your coding tips...


Remy Lebeau (TeamB) wrote:
> "Colin B Maharaj" <noreply@myhost.com> wrote in message
> news:41175fe0@newsgroups.borland.com...
> 
> 
>>Hi all, is there anyway to get the dimensions of a jpeg
>>without opening it and loading it into a Bitmap memory block.
> 
> 
> TJPEGImage inherits Width and Height properties from TGraphic.  You don't
> need to convert to TBitmap first:
> 
>     AnsiString MakeJPEGHtmlWrapper(TStringList * L)
>     {
>         //...
>         TJPEGImage *jpg = new TJPEGImage;
>         //...
>         jpg->LoadFromFile(B);
>         //..
>         A += ( "width: " + IntToStr(jpg->Width) + "px; height: " +
> IntToStr(jpg->Height) + "px; \">" );
>         //...
>         delete jpg;
>         //...
>     }

Re: JPEG properties

#442

Author: Vladimir Stefanovic
Date: Tue, 10 Aug 2004 20:17

14 lines
1347 bytes

> Is there a way I can read the header and get the dimensions?

In any case you have to open the file into TImage or by fopen().
Once I needed the same thing and I discovered which bytes makes
Width and which Height. You can find them fast by any HEX editor.
I remember that they are not at the same offset of the file, but are
surrounded with the same byte pattern.

I abandoned that approach when I found the TWO such patterns in
one of (maybe) 100 JPG files.


Best regards,
Vladimir Stefanovic

Re: JPEG properties

#443

Author: Remy Lebeau (TeamB)
Date: Tue, 10 Aug 2004 20:50

16 lines
1495 bytes

"Vladimir Stefanovic" <spam@not.needed> wrote in message
news:41192d5c@newsgroups.borland.com...

> In any case you have to open the file into TImage or by fopen().
> Once I needed the same thing and I discovered which bytes makes
> Width and which Height. You can find them fast by any HEX editor.
> I remember that they are not at the same offset of the file, but are
> surrounded with the same byte pattern.

You shouldn't be making assumptions on byte patterns.  Go to
http://www.wotsit.org and grab the specification for the JPG format.  Then
you don't have to make guesses at all.


Gambit

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