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Yes, phone apps work, but they still require several clicks to get things right, and upload. But if your camera is fixed relative to the paper, then there is a

Yes, phone apps work, but they still require several clicks to get things right, and upload. But if your camera is fixed relative to the paper, then there is a single known transform that will correct perspective. If you write software to integrate directly with the LMS, then it will only require one hardware button press per page, to upload the assignment.

jjeaff 6y ago
Seems like to get it to work at such a sharp angle, you would need a very large depth of field with your lense in order to keep both the nearest and farthest portions of the page in focus.
- abdullahkhalids 6y ago
  I do have a phd in a theoretical quantum optics, so no, I have no idea if such a weird angle will actually work in practice given the physical and budgetary constraints. :-D Seriously, though, I have idea. We can take two pictures focusing once the near part, and once on the far part. If cameras are cheap (I haven't researched), maybe two on either end of the device would mitigate the complexity of the lenses required.
- commonvision 6y ago
  Depth of field isn't really an issue with wide angle lenses for smaller format sensors. The EFL is shorter which boosts the depth of field. The bigger problem is field curvature if the page is closer than ~6" - most of these lenses weren't designed for short object distances. For example, this 1.8mm F/2.8 low distortion lens has a hyperfocal distance of 0.2m (~8") on the Pi HQ: https://commonlands.com/products/low-distortion-m12-lens https://commonlands.com/products/low-distortion-m12-lens and easily covers 6"-25" depth of field.
ska 6y ago
Really the transform isn't as much trouble as getting a uniformly lit area with good contrast.
- abdullahkhalids 6y ago
  Yes, that could be problematic, hence I incorporated the LED in my proposal image. As we are working with standard paper, we know its color (as it appears to the camera in neutral light). We could have a calibration step, where the multicolored LEDs are tuned to get the right contrast and color balance. Though, I have no idea how well it will work in practice.
  - deleted 6y ago
    [deleted]
  - totetsu 6y ago
    The light would be stronger closer to the source. Better to have a stand like the Czur scanners, and the pi on top

jjeaff 6y ago

Seems like to get it to work at such a sharp angle, you would need a very large depth of field with your lense in order to keep both the nearest and farthest portions of the page in focus.

abdullahkhalids 6y ago
I do have a phd in a theoretical quantum optics, so no, I have no idea if such a weird angle will actually work in practice given the physical and budgetary constraints. :-D Seriously, though, I have idea. We can take two pictures focusing once the near part, and once on the far part. If cameras are cheap (I haven't researched), maybe two on either end of the device would mitigate the complexity of the lenses required.
commonvision 6y ago
Depth of field isn't really an issue with wide angle lenses for smaller format sensors. The EFL is shorter which boosts the depth of field. The bigger problem is field curvature if the page is closer than ~6" - most of these lenses weren't designed for short object distances. For example, this 1.8mm F/2.8 low distortion lens has a hyperfocal distance of 0.2m (~8") on the Pi HQ: https://commonlands.com/products/low-distortion-m12-lens https://commonlands.com/products/low-distortion-m12-lens and easily covers 6"-25" depth of field.

ska 6y ago

Really the transform isn't as much trouble as getting a uniformly lit area with good contrast.

abdullahkhalids 6y ago
Yes, that could be problematic, hence I incorporated the LED in my proposal image. As we are working with standard paper, we know its color (as it appears to the camera in neutral light). We could have a calibration step, where the multicolored LEDs are tuned to get the right contrast and color balance. Though, I have no idea how well it will work in practice.
- deleted 6y ago
  [deleted]
- totetsu 6y ago
  The light would be stronger closer to the source. Better to have a stand like the Czur scanners, and the pi on top