Unraveling Auto Focus: Cameras and Math

In summary, the conversation discusses how auto-focus works in cameras. It is explained that cameras divide the picture into different regions and further subdivide them into tiny areas to detect edges. The differences in color and sharpness are measured to determine if the image is in focus. There are two types of auto-focus, active and passive, with passive using edge detection. The conversation also mentions the use of histograms and various edge detection techniques, such as Sobel Edge Detection. It is noted that different cameras may use different filters.
  • #1
Dilbert
36
0
hello,

i am not sure that this is the correct forum to post in, but i am confident that the moderators can swiftly correct my error if that is the case.

I was wondering a little about cameras and their auto foucs. How does it work and what is the math behind it?
 
Mathematics news on Phys.org
  • #2
the camera divides the picture it, erm, sees, up into different regions, the shape of this initial division varies from camera to camera, and some have several different divisions that it will use depending on if you're taking a landscape shot or a portrait. a portrait shot will put more emphasis no hte central area. now in each area it further subdivides into tiny little areas and then tries to work out what are edges. if it's in focus then the edges are sharp which basically means that the colours in two closely position areas will be very different each side of the edge. if it were out of focuse the drop off, or change in colours etc would be less sharp. it then adds these differences up (i don't know wxactly how it assigns numbers, it will differ in different cameras) and then weights it for the larger area it's in - more weighting for the centre) and then if the number it comes up with is small enough it decides if it's in focus enough. that is roughly how it works, i think.
 
  • #3
so, it is basically edge detection?
Then i have solved the math allready, i just thought it was more complex.

Thanks Matt.
 
  • #4
Actually, there are two types of auto focus, one is active, the other is passive. Active sends out an infrared beam of light and it bounces back to the camera and then gets measured to determine how far away things are. Passive is like described above, it is a pretty simple idea, but making it work is not as easy as it sounds.
 
  • #5
Yes, auto-focus just applies a digital edge-detection filter to the incoming images, and adjusts the focus until the edges are as sharp as possible. Alternatively, the processor may just look at a histogram of the incoming images and adjust the focus to maximize the spikes on the histogram.

- Warren
 
  • #6
thanks Warren.

Obviously having a histogram would contribute a lot.
 
  • #7
might be a stupid question but, there are several edge detection techniques. Sobel Edge Detection for instance.

What kind of edge detection does the cameras use ? i guess that it can vary from the different brands but is there any mainstream edge detection filter? In that case, which?
 

1. What is auto focus and how does it work?

Auto focus is a feature found in cameras that allows the lens to automatically adjust and focus on the subject of a photo. It works by using sensors to detect contrast in the image and then adjusting the lens to achieve maximum sharpness.

2. How does math play a role in auto focus?

Math is used in auto focus algorithms to calculate the distance between the camera and the subject. This information is then used to adjust the lens to achieve the desired focus.

3. Are there different types of auto focus systems?

Yes, there are several types of auto focus systems, including contrast detection, phase detection, and hybrid systems. Each type uses different methods and technologies to achieve focus.

4. Can auto focus be manually adjusted?

In most cameras, auto focus can be manually adjusted by switching to manual focus mode. This allows the user to manually adjust the focus of the lens instead of relying on the camera's auto focus system.

5. How does auto focus affect the quality of photos?

The quality of photos can be affected by auto focus if it is not functioning properly. Improper focus can result in blurry or out of focus images. However, when the auto focus is working correctly, it can greatly improve the sharpness and overall quality of photos.

Similar threads

Replies
10
Views
344
  • Computing and Technology
Replies
23
Views
2K
Replies
1
Views
905
Replies
3
Views
895
  • STEM Academic Advising
Replies
4
Views
553
  • General Discussion
Replies
5
Views
632
Replies
6
Views
3K
Replies
4
Views
1K
Replies
3
Views
1K
Replies
6
Views
3K
Back
Top