Question

This one should be pretty easy..

Asked by: asymmetric

Delphi 6 Enterprise Edition.
TJPEGImage (from included jpeg unit)
TMemoryStream

jpegimage.assign(bmpcurrent); // bitmap -> jpeg
jpegimage.jpegneeded; // yep, I need one
jpegimage.compress; // go go go
jpegimage.savetostream(memorystream) // need a stream to send out via Indy TIdHTTPServer

memorystream.size = 0 -- that sucks

memorystream.position := 0;
memorystream.size = 0 -- still sucks

memorystream.seek(0, 0);
memorystream.size = 0 -- sucks again!

Three sucks and you're out!

Oh, just for the heck of it..
jpegimage.savetofile('c:\test1.jpg');
memorystream.savetofile('c:\test2.jpg');

test1 is fine, test2 is created, proper dimensions, but entirely black.  This is intermittent, but seems to happen more often than not.

Is there some other way of getting the jpeg into the stream?  I'm pretty sure it's there, but with a size of zero, it's not doing me much good.  I really wish the source to the jpeg unit came with delphi.

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Asked On
2003-05-07 at 17:16:42ID20609235
Tags

delphi

Topic

Delphi Programming

Participating Experts
4
Points
250
Comments
13

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Answers

 

by: Slick812Posted on 2003-05-07 at 21:15:17ID: 8485047

hello asymmetric, maybe you need to give the JPeg some info on HOW TO COMPRESS


TempJpg := TJpegImage.Create;
  with TempJpg do
    begin
      PixelFormat := jf24Bit;
      Scale := jsFullSize;
      Grayscale := False;
      Performance := jpBestQuality;
      CompressionQuality := 74;
      ProgressiveDisplay := True;
    end;

TempJpg.Assign(Bmp1);
JStream := TMemoryStream.Create;
TempJpg.SaveToStream(Jstream);
Jsize := Jstream.Size;

 

by: asymmetricPosted on 2003-05-07 at 21:35:00ID: 8485098

The jpeg is working.. I use jpegimage.savetofile often and it's fine.. quality at 80, performance left default..

It's something about the stream and its interaction..

 

by: kretzschmarPosted on 2003-05-07 at 23:53:24ID: 8485662

just to ask, why you want to set the size to 0 after
you've properly stored the jpeg into the memorystream?

 

by: Leety_McleetPosted on 2003-05-08 at 00:42:04ID: 8486017

Hmm, i recently have been having a few problems reading and writing to TMemoryStreams, and im not too sure but it could be a bug...

Anyways, the way i ensured the data was ok every time was i used the Move() function

i.e.
Move(source, destination, bytes to copy);
Move(jpegimage, memoryStream.Memory^, sizeof(jpegimage));


Not sure if the parameters are exactly right, you might have to put a '@' at the start of jpegImage or whatever, but take a look at the API..

I found in my sound example that using saveToStream and LoadFromStream commands actually added some garbage bytes at the beggining....

this could be the problem thats plaguing you :)

regards,
L33ty

 

by: andrewjbPosted on 2003-05-08 at 01:16:50ID: 8486227

Just to make sure...

you've not done something daft like forgetting to create the memorystream object have you... (we don't see the supporting code in your example)

 

by: asymmetricPosted on 2003-05-08 at 09:56:15ID: 8490196

No, I'm creating the stream.. ;)

And to leety.. I'm not setting it to zero, that was a single =, not a :=.  I was just showing that it was equal to zero in the watch window, which causes no end of problems.

The problem is, after the jpegimage.writetostream, the stream doesn't reflect the correct size.. so I don't know how much data was written to it.

 

by: kretzschmarPosted on 2003-05-08 at 10:33:04ID: 8490499

use slick's advice, should work

 

by: asymmetricPosted on 2003-05-08 at 10:53:31ID: 8490647

Ok, I thought I'd give you some more news.. I'm not sure what could be causing this, but I've been working on this all morning.

I have two routines, one that captures the image off a timer, one that does it immediately with a button click.

The one with the timer is the one having the problem, the buttonclick one works fine..

If I call the button click routine from inside the timer event, it works fine.  If I copy the code from the buttonclick into the timer, it goes back to the prior behavior of being the right dimensions but entirely black.

The code in the buttonclick is dead simple :

        sDestfile := FileCaptureFrame;
        if sDestfile <> '' then
          SaveImage(sDestfile);


FileCaptureFrame is a routine that gets the image from the device (bitmap), applies a caption, and just returns me the proper filename.  It works fine, no matter where I call it from, at least as far as I can tell.

SaveImage is also a simple routine that in the case of the jpeg, just calls jpegimage.savetofile

I'm starting to suspect some subtle threading issue, even though the application itself isn't threaded, it is making directx/directshow calls to grab the frame from the device.. and maybe the calling context is screwy from the one routine to the other.  I can't for the life of me think what that difference might be though.

 

by: asymmetricPosted on 2003-05-08 at 10:55:25ID: 8490667

Oh I should just note, this has gone deeper than the stream problem.  Apparently it's a problem with where I'm calling these routines from, and not the stream/jpeg objects themselves, although they could be to blame for the dependency.

 

by: Slick812Posted on 2003-05-08 at 13:08:01ID: 8491445

just a Guess, , ,some "State" of your Direct X capture needs to be upDated, reInitialized,  or get a more current reading, when you use the timer, check any variables that are set before the timer event and used in the timer event

or you might try to use the same External function of Image capture in the Button Click and the Timer, or maybe just call the button click procedure in the timer

 

by: asymmetricPosted on 2003-05-08 at 14:16:39ID: 8491866

Slick, I was doing like you suggest, using just one routine to grab the JPEG @ 1FPS.  I added code for the internal http server, which was trying to write that jpeg to a stream, and that's what didn't work.

More investigation found that calling those routines from inside an event handler for the Indy TIdHTTPServer component was causing the problem.  I have a routine called CaptureAndCaptionFrame, which grabs the image from the device, applies the caption, and stores the bitmap and jpeg.

I added a call to that before the jpegimage.savetostream and everything is working ok.  The "deeper" problem I mention in my last posting was just a result of me breaking some code while trying to fix this stream thing.

Everything is working ok now, thanks to everyone for your suggestions, it turns out I think it's just a thread issue with the Indy component somehow coupled with the exposure of certain properties/procedures on the form that has all the directx components.  Whatever the case, I'm up and running.

 

by: asymmetricPosted on 2003-05-09 at 23:05:54ID: 8498847

Close enough and since It's all sorted out, I don't think there will be any more posts that point to the "real" culprit here.. which I have yet to find for sure.

Thanks everyone for your input.

 

by: asymmetricPosted on 2003-05-09 at 23:07:36ID: 8498852

Ok I tried to accept this once already and apparently it didn't take.

Answer is close enough to what I've guessed myself, even if I can't find a solid way to confirm it.  Such are the problems with DX and other 3rd party stuff like Indy and MS COM.

Thanks everyone for your input.

20120131-EE-VQP-002

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