Re: Long change-over times in AmCap, StillCap
From: Thore Karlsen [MVP DX] (sid_at_6581.com)
Date: 11/18/04
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Date: Thu, 18 Nov 2004 09:29:20 -0600
On Wed, 17 Nov 2004 17:48:29 -0600, Hans-Jochen Trost
<dont-email@but.post-re.ply> wrote:
>All,
>
>I need to run a fairly simple display app for 2 cameras. One or the
>other shall be displayed on the computer screen at any time. One of
>the two cameras needs to get a cross hair overlaid on the computer
>screen at all times during live display. Speed is not very critical,
>i.e., I can easily sustain losses relative to 30 fps. I also need to
>occasionally secure an individual frame as a bitmap image to hand to a
>machine control program to process, or to save to hard disk.
>
>My hardware is PC104+ based, with a 166 MHz Pentium with MMX, 128 MB
>RAM, Windows 2000 Pro SP4, and I develop (on a different machine) with
>VC++6 and DirectX 9c. The frame grabber uses the Conexant BT878 chip,
>and AmCap and StillCap are able to handle it. That cpu does a fine
>job for everything else, including the main objective of the machine
>that it controls.
>
>I tried to work from AmCap but couldn't get the capture to file part
>to work (I'm new to DirectX). Then I started from Stillcap and had
>some success, basically because I could leave all the DirectX stuff as
>is and tweak the GUI and other supporting code for my needs.
>
>The big problem is, in either case, that not only the start-up of the
>programs is slow - 4-5 seconds for the bare unchanged samples, more
>for my modified StillCap (interface made similar to AmCap, for larger
>image display) - but when asking to capture a still image, it takes
>ages to stop the preview, to capture a single image into a file, and
>restart the preview. It looks to me as if the whole underlying graph,
>or at least most of it, is dismantled and an alternative one
>constructed at every switching operation.
Yes, and the problem is that the capture filter is incredibly expensive
(time-wise) to create and destroy. You definitely want to make the graph
once and keep it around until you don't need to capture any more.
>Questions:
>
>Are there ways to get those switching times down by a factor of 10?
>
>How difficult/problematic would it be to run two apps simultaneously,
>one doing preview display all the time, the other grabbing a still
>image occasionally from the same source?
Why would you want to have two apps instead of one?
I'm not sure how StillCap works, but it seems to me that the best way to
do this would be to create the graph with a sample grabber filter (see
the DX documentation) and keep the graph running, getting frames from
the sample grabber when you need it.
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