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Sony VX2100 / PD170 / PDX10 Companion
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Old October 11th, 2006, 04:59 AM   #1
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VX2100:Still-capture Quality Comparisons

I've been trying to capture some still images from pre-recorded DV tape onto a MemoryStick, using my VX2100. I've determined that the results of this will be mostly mediocre, at best. However, when I've directly captured stills from the VX2100 camera onto the MemoryStick, most of them look very good, considering that they have just a 640 X 480 pixel-size and use an average of 175 Kb.

The difference is that those taken from tape have been encoded and compressed for DV and then recompressed a second time for the J-PEG images. This double-compression badly degrades the quality. Also, when a VX2100 (and some other similar models) are in direct-capture memory mode, they use progressive scan and a fast mechanical shutter. I'm going to be snapping even more memory-mode stills along with my video tape footage, as this small pixel-size is very useful on the Internet.

I've included two sets of comparison shots. They show the same birds at the same times, although not in identical poses. The pixel-size is the same for all, although the memory mode pictures have a slightly larger bit-size. When the pictures are expanded to full-size, the difference in quality is even more pronounced. They show two hybrid geese, which are crosses between Canada and domestic Greylag Geese. If I had to tell you which are from tape and which are captured camera-direct, my thesis here would be invalid.
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VX2100:Still-capture Quality Comparisons-dsc00314.jpg   VX2100:Still-capture Quality Comparisons-dsc00053.jpg  

VX2100:Still-capture Quality Comparisons-dsc00091.jpg   VX2100:Still-capture Quality Comparisons-dsc00054.jpg  

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Old October 11th, 2006, 10:27 AM   #2
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How interesting.

Is the 1st pic from a memory stick and the 2nd pulled from a dv tape?

Is the 3rd from a memory stick and the 4th pulled from a dv tape?
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Old October 11th, 2006, 10:43 PM   #3
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Originally Posted by Richard Zlam
How interesting.

Is the 1st pic from a memory stick and the 2nd pulled from a dv tape?

Is the 3rd from a memory stick and the 4th pulled from a dv tape?
That is correct. However, both sets of pictures ended up on the same MemoryStick.

I'll point out another annoyance I only recently discovered about my Sony DV equipment: My GV-D1000, a mini-DV VCR that has a MemoryStick slot and a USB port, has even more limitations on the picture quality of the J-PEG stills it produces. My Sony camcorders have the capability to produce stills from a choice of Standard/Fine/Superfine quality and use about 175 Kb. for the highest level 640 X 480 pictures. But, the GV-D1000 doesn't go higher than the Fine mode, using about 75 to 95 Kb. A still that's pulled from a tape recording and given so few Kb., is too poor in quality for anything I can imagine.

Here's an example I made camera-direct onto a MemoryStick in the MegaPixel TRV730, using the Superfine mode with 510 Kb. and its highest pixel-size setting of 1152 X 864 (The VX2100 doesn't go above 640 X 480 in pixel-size). The second picture here was taken off a FireWire input from a Digital8 VCR's tape playback, using the GV-D1000 VCR's MemoryStick to capture it as a J-PEG. Its pixel-size is 640 X 480 and has 79 Kb. On a video screen in realtime playback, this original scene looked bright and sharp, coming from the TRV730.

Since these two images originated with the same camera and the scenes seemed to have about the same resolution on videotape, the quality-reduction from doing a still-capture from tape is obvious. There's a pixel-size difference between these two pictures, but that accounts for only part of the gap in image quality.
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VX2100:Still-capture Quality Comparisons-dsc00058.jpg   VX2100:Still-capture Quality Comparisons-dsc00020.jpg  


Last edited by J. Stephen McDonald; October 11th, 2006 at 11:23 PM.
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Old October 23rd, 2006, 04:01 AM   #4
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In PAL land we have a bigger difference between Memorystick stills (640 x 480) and off tape (720 x 576) so there's no contest over here - even with the 'double compression'.

tom.
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Old October 23rd, 2006, 09:40 PM   #5
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Originally Posted by Tom Hardwick
In PAL land we have a bigger difference between Memorystick stills (640 x 480) and off tape (720 x 576) so there's no contest over here - even with the 'double compression'.

tom.
I was under the impression that when an image was captured from a standard-definition videotape and converted to a J-PEG on a MemoryStick, that its pixel-size would be only 640 X 480, regardless of whether it came from a PAL or NTSC recording. The higher resolution of a PAL video recording might give an advantage to an image captured from it. However, I'm sceptical about this being enough to offset the double DV/J-PEG compression that takes place. Are you implying that you get a sharper 640 X 480 J-PEG from a PAL DV recording than if you captured it directly from the camera in Memory Mode?
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Old October 27th, 2006, 03:54 AM   #6
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No Steve. PAL users get the sharpest stills off tape when the camera's shooting in progressive scan mode.
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