image formation Flashcards
(30 cards)
What does the aperture in an imaging system do?
It limits the range of light rays that reach the sensor to reduce blur and improve sharpness.
What is a common problem when no aperture is used in front of a sensor?
Multiple light rays from different scene points hit the same pixel, resulting in a blurry image.
What is the trade-off of making an aperture very small?
It reduces brightness and introduces diffraction, which causes blur.
What is diffraction in imaging?
The bending and blending of light as it passes through a small aperture, which leads to loss of image sharpness.
What is the function of a lens in image formation?
It focuses incoming light rays from a point in the scene onto a point on the sensor.
What does the focal length of a lens depend on?
The shape of the lens and its refractive index.
What is the thin lens equation?
1/f = 1/u + 1/v, where f is the focal length, u is the object distance, and v is the image distance.
What does image enhancement aim to do?
Improve visual quality by reducing artifacts like noise, blur, haze, or resolution limits.
What are common types of image enhancement?
Denoising, deblurring, super-resolution, dehazing, and deraining.
What is image noise?
Unwanted variations in pixel values that degrade image quality.
What causes image noise?
Sensor imperfections, environmental interference, and low-light conditions.
What is thermal noise in images?
Random electron fluctuations in sensors, often modeled as additive Gaussian noise and linked to ISO.
What is shot noise in images?
Random variations in photon arrival, modeled as Poisson noise, proportional to light intensity.
What is replacement noise in images?
Also known as salt-and-pepper noise, it includes dead (dark) and hot (bright) pixels.
What is speckle noise?
Granular interference that commonly occurs in medical and radar imaging.
What does SNR stand for in imaging?
Signal-to-Noise Ratio.
What does a high SNR indicate?
A cleaner image with stronger signal relative to noise.
What is the formula for SNR?
SNR = P_signal / P_noise, where P is power.
What is image dehazing?
The process of removing atmospheric haze from images to improve visibility and clarity.
Why is image dehazing important?
It enhances image quality and is critical in applications like photography and self-driving cars.
What is the haze formation model equation?
I(x) = J(x) * t(x) + A * (1 - t(x)), where I is the observed image, J is the true scene, t is transmission, and A is atmospheric light.
What does the transmission map t(x) represent?
The portion of scene light that is not scattered and reaches the camera.
What does atmospheric light A represent?
Ambient light scattered in the atmosphere, contributing to the hazy appearance.
What is the dark channel prior?
A method based on the observation that in haze-free outdoor images, at least one colour channel is very dark in most patches.
