faint rain [deleted] 12:18pm, 17 February 2007
My first (hm...headless) self-portrait. I wonder why my shadow looks so normal compared to the trees. Only slightly distorted. Someone can explain that?

Me and my shadow
admin
clickykbd PRO 12 years ago
Was this a camera-phone by any chance? We've seen a lot of images having this "effect", especially in the cheaper camera-phone genre of cameras. It's really wonderful I think. And I believe it to be due to a digital equivalent of a focal-plane shutter distortion... albeit in a shutterless camera that is scanning a scene line by line (slow enough to register perspective change as it proceeds down the frame). It will tend to be exaggerated on one side or the other depending on which part of the "frame" had more induced motion by the throw... things closer to the axis of rotation will exhibit less of this distortion.

Lots of great stretching/warping/twisting is possible with cameras like these. Check out ferro's phone-cam tosses for lots of examples! He even has a couple that capture 3 distinct horizon lines!
faint rain [deleted] 12 years ago
Thanks for your reply clickykbd.
Right guess - it´s a K750i that I used - as for all my other tossing pics, but it was the first times I noticed that particular effect. So far, your explanation sounds logical, but I have to admit that I am no expert. Have to read about it.
And yea, I know ferro´s pics and I like them very much.
Sebastian- 12 years ago
As a physicist, I'd say that your picture is distorted due to the rotation of the camera, and so is your shadow.
Consider this: It's hard to say whether your shadow is only slightly distorted, since you don't know what it looked like originally. The original shadows in the image were probably pretty stretched out and tilted to the left, the motion of your camera happens to counteract this and now the shadows are leaning a bit to the right.
admin
clickykbd PRO 12 years ago
You can see the effects of focal-plane-shutter distortion with any camera that utilizes this type of shutter... the most common seen is a slight slanting effect of objects/scenes in motion... consider photographing a vertical pole from a car at high speed. With high enough shutter speeds the "slit" is smaller than the film frame... as the slit proceeds down the frame it records the pole at an angle... induced by the motion.

My suspicion, as I said in previous post... is that these cheaper "shutterless" digital cams utilize a digital process that is equivalent to a single pixel row shutter... and it scans the scene left to right, or top to bottom... very rapidly... but not rapidly enough when extreme camera motion is present. Since the motion of the camera is rotation the actual distortion is more complex than a "slanting" of the scene... it's more of a stretching and pinching that depends on what direction the scene was moving, and how fast, relative to this process of scanning line by line at the sensor. Fancier cameras are capable of caching this information in one take... and then reading from the sensor afterwards... but fancier cameras also tend to have mechanical shutters... and just like film cameras... should still be able to produce focal plane distortions. So perhaps a better name for what we see in cameras like yours is actually "sensor-read-distortion" ;-)
faint rain [deleted] 12 years ago
Another example. And i copied that from www.maisonbisson.com/blog/post/10531/
A digital camera’s imaging element, either a CCD or CMOS sensor, is made up of pixels that are organized into horizontal lines that are then stacked to make a picture. And the camera takes the picture by reading each pixel from left to right, line by line, from top top bottom. In the end, pixel number one in the upper left corner of the frame is sampled long before pixel five million in the lower right.
DSC00733
sweet
admin
clickykbd PRO Posted 12 years ago. Edited by clickykbd (admin) 12 years ago
Yup that's pretty much it, and as you suggest it's even more complex than a simple top to bottom difference... there is a left to right time difference as well PER ROW! Good find that link... especially good if you follow his link to Andrew Davidhazy, professor of Photographic and Imaging sciences at RIT.
faint rain [deleted] 11 years ago
Just found out that someone wrote a paper about our camera distortions. They call it the rolling shutter effect.
Here you can download it as pdf:
arxiv.org/abs/cs/0503076
It´s called:
Geometric Models of Rolling-Shutter Cameras; Marci Meingast; 29 Mar 2005
admin
clickykbd PRO Posted 11 years ago. Edited by clickykbd (admin) 11 years ago
from the abstract:
We also develop approximate projection equations for a non-zero angular velocity about the optical axis and approximate the projection equation for a constant velocity screw motion. We demonstrate how the rolling shutter effects the projective geometry of the camera and in turn the structure-from-motion.

Yup! Exactly what they are talking about. Makes you wonder how long before there is a photoshop filter for it. Although a camera toss isn't even as simple as this rotation they cite. The center of gravity is not always on the focal axis, and the scene is changing relative to this oddly rotating camera on the parabola of the trajectory due to gravitation.

However, if they expand their equations for all types of motion, and know the properties of a particular CMOS, they could effectively "Un-toss" a photo in post production or realtime. Which is their goal relative to improving cheap cameras as sensors for robotics.
admin
clickykbd PRO 11 years ago
Actually a closer read, and they are talking about "using" the property to create structure-form-motion sensors. They discuss correction a little bit but there is another article on that here:

Rolling shutter distortion correction
Liang, Chia-Kai; Peng, Yu-Chun; Chen, Homer; 07/2005
2005SPIE.5960.1315L
adsabs.harvard.edu/abs/2005SPIE.5960.1315L
Groups Beta