AstroYacker Software for MacOS X
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AstroYacker, in technobabble, uses the Quartz Graphics engine through the Cocoa Application Classes to provide high quality quick affine transformations for translations, rotations, flipping and scaling (and, more importantly, all at once). It interfaces to QuickTime and compression components through the Carbon framework, but where possible most processing is done in Cocoa. It is multithreaded with pre-emptive threads, using the Distributed Object technology to avoid re-entrancy problems. It is designed to be robust, user and other application friendly.
The source movie is 640x480 pixls and show in the upper left. It shows Mars at an angle. In the larger view we see the effect of rotating and scaling the movie's frame. The twisted original frame is shown in mid gray. The black inner 160x160 square (with a subtle orange border), is the size of intended output movie. The dashed white lines show where AstroYacker's alignment algorithm thinks Mars is. There is a very subtle orange crosshair through showing the center of the alignment also. The Show Alignment check box shows or hides the alignment graphics.
When generating the output, AstroYacker, according to the window's setting would dither the alignment by up to 8 pixels horizontally and vertically (this is to minimize the blocking artifacts of JPEG style image compressors used in the output movie compression). This dither can be seen when the "Process Frames" button is pressed and processing begins.
Here we see the results of the processing. The source movie is shown behind the new smaller destination movie.
The movie controls are tied to the main view show you can fully preview the processing effects before generating the output movie. All image manipulation shows effects in real-time even when the movie is playing. Settings such as scaling can be controlled by either, typing a scale factor into the text box, clicking the stepper up and down (fine control) or using the slider (coarse control).
Rotation and Parallatic Correction
To correct for progressive field rotation (Parallatic angle with alt-azimuth mounts), move the Movie to the start either through the mini movie QuickTime controller or (better) using the appropriate button down the bottom of the window. Adjust the Start Angle to orient the object to your aesthetic taste. To get more precise alignment use the scale control to zoom in (remember to return this to the setting you want before starting the processing otherwise the output will show this scaling). Now step through the first few frames of the movie on the QuickTime controller on the mini movie to check the rotation align in case your first frame is anomolous. Now even if the capture is only a few minutes the rotation needed at the end of the Movie will be different from the start (even if only a few degrees it is easily noticable). To make this correction go to the end of the movie using the appropriate button down the bottom of the window, or otherwise. Now adjust the Range angle to get the end rotation right. Back step a few frames from the end to check the last frame is not anomolous. Finally to see the overall effect use the Time slider at the bottom or hit the play button on the mini movie.
A sample movie to illustrate AsytoYacker's reject frame algorithm. Download (Large) Mini Movie (744 kB)