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Old Dec 4, 2008, 2:29 AM   #11
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adric22 wrote:
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Well, I must have missed this thread the other day. But I can add some input to it. First off, I haven't looked at your video. Right now I'm using my old Apple iBook 366 Mhz, so it isn't nowhere near fast enough to play that video. But when you described it, I knew exactly what you were talking about. I've noticed my Aiptek IS-DV2 does something similar. When I first noticed it, I too got the impression it was being upscaled or "interpolated" to 640x480 from some lower resolution.

So, I did some testing. I put the camera in 320x240 mode and took some shots of the same items, and also used a different camera in 320x240 mode. Then I carefully compared the images in 640x480 to the ones in 320x240. My conclusion? Baffled. I mean, honestly, it is very confusing. There are jagged lines noticable in many objects that have high-contrast straight edges and the detail on these objects is similar in both resolutionsl Yet, other objects that have less contrast to them, I can see considerably more detain in the 640x480 mode. Which means the camera is definately taking video at 640x480. Yet, there is something in the way their compression works that causes high-contrast edges to have less detail. I suspect it is a cheaper way to do on-the-fly MPEG4 encoding.
I did not post any video, they are just a single frame from each mode, comparing the same shot. It's a 2 meg file I believe. Yeah I'm sad about the jaggies, I actually got to the point where I was able to live with the SLANT of the CMOS rolling shutter then I came across these jaggies. Weird. The only resolution I do NOT see them in is the 1080p res, which is what I'm trying to stick to now... but since it's only 30fps the slant of the rolling shutter is WAY more obvious... this is why I think I won't be upgrading any time soon, until a 60fps 1080p option is available. I just don't have the funds for a high end camcorder, plus I honestly do love how easy this one is to carry around for everyday use!
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Old Dec 4, 2008, 10:31 AM   #12
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Pgomberg, sorry I didn't realize they where just still photos.

Yeah, I just checked them out and I definately see what you are talking about. It IS puzzling, considering the 1080p does not have that problem.

I have 2 theories on the matter.

Theory #1) As we all know, the image sensor has more pixels on it than we need for making a video. Aiptek and the like tend to just grab the pixels it uses, not even reading the pixels in between. Where high-end cameras tend to take all of the pixels and interpolate them to allow better light pickup and more clarity. Of course, this requires extra hardware or extra CPU power in the camera. It is possible that the arrangement of pixels on the image-sensor is such that when capturing at certain resolutions, such s 720p, there is just too much space between the pixels it is capturing. Perhaps the D1 doesn't suffer from this because the lower resolution allows them to interpolate more pixels?

Theory #2) The image sensor itself may only have certain "modes" that it can capture images in. Maybe there is no mode for 720p, so it must scale down from a 1080p and the scaling method it uses does not use any interpolation, just cuts pixels out for extra speed. (or lazy programmers?)

At least the D1 resolution isn't affected. That is good because I have a feeling if I ever bought one of these HD cameras I'd be using the D1 resolution a lore more than the HD resolutions.
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Old Dec 4, 2008, 11:00 AM   #13
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adric22 wrote:
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Pgomberg, sorry I didn't realize they where just still photos.

Yeah, I just checked them out and I definately see what you are talking about. It IS puzzling, considering the 1080p does not have that problem.

I have 2 theories on the matter.

Theory #1) As we all know, the image sensor has more pixels on it than we need for making a video. Aiptek and the like tend to just grab the pixels it uses, not even reading the pixels in between. Where high-end cameras tend to take all of the pixels and interpolate them to allow better light pickup and more clarity. Of course, this requires extra hardware or extra CPU power in the camera. It is possible that the arrangement of pixels on the image-sensor is such that when capturing at certain resolutions, such s 720p, there is just too much space between the pixels it is capturing. Perhaps the D1 doesn't suffer from this because the lower resolution allows them to interpolate more pixels?

Theory #2) The image sensor itself may only have certain "modes" that it can capture images in. Maybe there is no mode for 720p, so it must scale down from a 1080p and the scaling method it uses does not use any interpolation, just cuts pixels out for extra speed. (or lazy programmers?)

At least the D1 resolution isn't affected. That is good because I have a feeling if I ever bought one of these HD cameras I'd be using the D1 resolution a lore more than the HD resolutions.

Sadly the D1 *IS* affected. I had misspoke earlier. If you look at the pics again, you will notice that D1 is also affected. I suspect your Theory #2 is probably correct. Perhaps the only "native" mode of this sensor is 1080p, but capable of other custom modes and they have a poor implementation of resizing. Or it could be the CMOS sensor itself, since the DOF changes between the D1, or 720p resolutions and the CIF and 1080p ones. The latter having a much closer FOV. This must give us some hint as to what is going on with the camera.. but I'm just not versed enough in this stuff to figure it out conclusively. The changing DOF/FOV is not optics, it's electronic. So if you can get a CLEARER picture with 1080p but with a closer FOV, then perhaps these are modes preprogrammed into the CMOS which Aiptek cannot overcome their defects? If the optics don't change from D1, 720p, and 1080p modes, this means then that the CMOS sensor is actually using LESS of it's image sensor space to capture the 1080p (because it shows up as a closer FOV). Therefore if LESS of the image sensor is capable of having such a clear picture, with no distorted lines, you would naturally conclude that using MORE of the CMOS sensor would ensure very clear and crisp details. Confusingly however, when switching to D1, or 720p modes, which use MORE of the CMOS sensor, you get these distortions in edges...

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Old Dec 4, 2008, 11:11 AM   #14
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Sadly the D1 *IS* affected. I had misspoke earlier. If you look at the pics again, you will notice that D1 is also affected.
I looked at the images, and the effect seemed much less in the D1 mode. In fact, it looked much better than the D1 images I've seen from my Aiptek (which is its highest resolution)

Although.. I must admit something I hadn't thought of earlier. I can think of another instance of something like this. My Sanyo CG6 fails to use interpolation when taking still-shots at 640x480. I usually only want to take 640x480 when I am making a photo for ebay or something like that. But my CG6 takes TERRIBLE still photos at that resolution. I always have to take them in 2 MP mode, and scale them down in a paint program.
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Old Dec 4, 2008, 9:32 PM   #15
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adric22 wrote:
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Theory #2) The image sensor itself may only have certain "modes" that it can capture images in. Maybe there is no mode for 720p, so it must scale down from a 1080p and the scaling method it uses does not use any interpolation, just cuts pixels out for extra speed. (or lazy programmers?)
That reminds me of the Aiptek PVR that I had which had terrible video compared to the MPVR. The video looked like it was way oversharpened to the point that you got serious moire effects on lines close together and it also looked like lines had jagged edges as well. There was a whole thread I did on this a while back.

I figured that it must be a resizing problem as you said, since I got the exact same effect if I took a 5MP image and resized it down to 640x480. I also tried this on a native 5MP image from my Minolta Camera just in case there was something strange about the 5MP CMOS sensor in the Aiptek PVR. If I used a resampled resize the image was much better.

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