What is total internal reflection?
Light is been refracted by travelling through an interface of two media with different refractive indices. If the light travels from the optical dense to the less dense material, you can reach a critival angle of incident. At this incident angle the refraction angle is 90°. If you increase the angle of incident. You get no refraction but total internal reflection.
How can total internal reflection been used in droplet dynamic applications?
As soon as a droplet is touching the glas surface, you change the refractive properties of the interface. With the right setup and the rigth angle of incident, it is possible to capture the reflected light (of the glas-air interface) while the light that hits the glas-droplet interface is not captured.
What are the challenges when imaging a dense spray?
You can not see inside the spray (e.g. the liquid core, different density regions) and visibly just capture the shadow/conture of the spray.
Describe the basic principle of ballistic imaging.
There are different paths through the spray:
balistic photons (direct path)
snake (quasi-balistic) photons (scattering 1-4 times)
diffuse photons (scattering multiple times)
The more direct the path of the photon is, the less time the photon takes to reach the camera.
This is used by ballistic imaging. The photons that penetrate through the spray are filtered by the time they take to reach the target. Then only the fastest will be captured.
What is the advantage of ballistic imaging?
With ballistic imaging you can see inside a dense medium (e.g. a spray).
What is the principle of holographic imaging?
You use monochromatic light to iluminate an object. Besides the reflected light of the object you capture the light of a reference wave with the same wavelength. The camera captures the interference of the two light sources and the information of the phase difference is captured in the brightness. The phase difference of the two light waves gives information of the 3d structure of the object.
A computer can reconsturct the 3D object.
Why do we need image processing?
How does a computer “see” an image?
A computer sees an array of integers, that represent the brightness of a pixel.
Explain bit and colour depth and give an example.
Each Pixel is represented by a number. The accuracy (amount of values) of brightness and colour depends on the depth:
1-bit: only black and white
8-bit: 256 shades of grey (or 3 bit red, 3 bit green, 2 bit blue)
24-bit: true color 8 bit for red, green and blue
What are the main image processing steps?
pre-processing:
data extraction
Name different pre-processing steps.
a. image representation
b. image restoration, rectification and correction
c. image enhancement
d. Selection of the Region of Interest
e. image transformation (e.g. binarization)
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