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Justin Nixon

DirectShow: DVD Applications & Video Processing

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I have a set of DVDs that contain hours of television transmissions from the moon of Apollo 15 astronauts. Unfortunately there is a serious problem with the colour for about 80% of the transmissions. Two of the component colours in the video signal have been swapped (usually blue and green but sometimes others). This results in the astronauts’ visors having a magenta instead of gold hue and the stars on the American flag having a green background. It’s quite off putting. I’ll try to explain the method used to transmit live colour TV pictures from the moon. The video camera used was, in fact, a monochrome camera designed to save weight and reduce transmission bandwidth. To turn this into a pseudo colour camera, a multi-coloured filter was electrically spun in front of the camera’s pick-up tube at 20rps. As each of the three component colours of the filter wheel passed in front of the pick-up tube, a monochrome frame was taken and transmitted back to Earth. Back on Earth, each of these frames were combined to generate a conventional colour TV signal. However, this will only provide true colours if the person combining the video, properly interprets the colour of the incoming monochrome frames. This is what has gone wrong with my DVDs – someone has been interpreting green as blue and vice-versa, which results in strange hues. The company that manufactured my DVDs should have spotted this problem, and it would have been very easy to correct at the authoring stage with some half decent video processing software. But they say it is not a serious problem (the red, white and green Stars and Stripes (!)) and that’s the way it is on NASA’s master tapes. I want to write a simple bespoke DVD application, probably based on the one supplied in the DirectX 8.0 SDK, which will permit me to swap any two component colours (selected using a dialogue) during playback so I can watch the DVDs on my PC in true colour. Is this possible? I’ve looked at the sample DVD application in the SDK, and I can’t find where in the source code the bitmap is actually rendered to the window so I can intercept and modify it. How do I gain access to the video bitmap? Thanks for any help. Justin. [edited by - Justin Nixon on March 6, 2003 11:29:21 AM]

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I''m not copying the DVD, I merely want to modify (correct) the output during playback.

I also don''t think it is hard to swap a couple of bytes per pixel in a "transform filter" unless the DirectShow API deliberately makes it impossible to access a DVD bitmap frame - I haven''t got that far yet, so I don''t know.

Justin.

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I've read a little more about DirectShow and it appears that writing transform filters for DVD playback has been denied to developers as a matter of policy not technical difficulty. No such restriction with MPEG-1 files, though. Sh*t!

Unless someone knows better (I've only just started learning DirectShow in the past few days), I guess I'll have to give up on this project.

Justin.

[edited by - Justin Nixon on March 8, 2003 8:14:52 AM]

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