how do camera sensors switch between resolutions

[rookie1010]

Hello,

i was wondering how camera sensors switch between resolutions.
Do they selectively turn of the sensors, like e.g. if a camera has teh following resolutions.

1600x1200
1280x960
640x480

and it wants to operate in 640x480 mode, does it turn of the (1600-640)x(1200-480) pixels

Do these sensors need to stick to a certain aspect ratio

i have got a phone camera which does the following ratios.

320x240
640x480
1280x1024.

any idea where it gets the extra pixels from, interpolation?

 

[OdiN]

It's probably just a function of the processor down-sizing the image - or upsizing (interpolating) depending on the camera. I don't believe it has anything to do with the sensor at all.

 

[fuzzybabybunny]

Originally posted by: OdiN
It's probably just a function of the processor down-sizing the image - or upsizing (interpolating) depending on the camera. I don't believe it has anything to do with the sensor at all.

Pretty much. It's all done in the camera's software. Not much else to it. Selectively turning off sensors would be way too awkward.

 

[rookie1010]

thanks for the reply,

so the sensor pixels can not be selectively turned on and off. i guess if all the pixels on the sensor are always active, in that case for a lower resolution image, less illumination is required?

 

[OdiN]

Resolution and exposure really are not related at all. It's going to take the same amount of light to properly expose a scene on a 1MP camera just the same as a 40MP camera.

 

[rookie1010]

thanks for the reply,

i thought that if a sensor has say 16 pixels and has 2 modes t ooperate in.

4x4 and 2x2

if the illumination is say 2 candelas, this would be distributed over 16 pixels. now if the resolutions is reduced t o2x2, in that case each effective pixel would get 4 times more illumination, in which case the required illumination may go down by a factor of 4??

 

[fuzzybabybunny]

Originally posted by: rookie1010
thanks for the reply,

so the sensor pixels can not be selectively turned on and off. i guess if all the pixels on the sensor are always active, in that case for a lower resolution image, less illumination is required?

Interesting way to think about it, but nope. You're probably thinking that on full resolution, since one sensor sensor = one pixel, at a lower resolution something like 4 sensor pixels = one pixel, right? And four sensor pixels supposedly capture more light than one sensor pixel... (it doesn't)

Doesn't really work that way. It goes:

Light -> Sensor -> outputs RAW image data -> file format

The first three steps are always the same. The sensor captures the same image data each time. What's different is what it does with this image data. In the case of outputting into a RAW file, no data is thrown away and it writes directly to the card. In the case of JPEG, it takes the RAW data and converts it into JPEG, writes JPEG to the card, and throws away the RAW data. In the case of different sizes, it takes the RAW file, converts it to JPEG, downsizes it, then writes the downsized JPEG to the card, then throws away the RAW data.

Basically it always records the RAW data first. Only difference is what it does with this RAW data afterwards. The sensor records the same full resolution RAW data each and every time. Sensor operation never changes unless you specifically increase its ISO.

 

[rookie1010]

thanks for the reply,

so in the RAW format, you will always get the same resolution?

 

[OdiN]

Originally posted by: rookie1010
thanks for the reply,

so in the RAW format, you will always get the same resolution?

Sorta.

There are some cameras that are now supporting "sRAW" which is a lower resolution RAW file. For these files, I would imagine it's just a downscaling as well but saved to a RAW format. But I'm not sure about that as it's a newer thing being supported.

 

[fuzzybabybunny]

Originally posted by: rookie1010
thanks for the reply,

so in the RAW format, you will always get the same resolution?

... usually...

I should probably amend a little of what I said above:

Light -> Sensor -> Outputs RAW data (ONLY THE CAMERA USES THIS DATA) -> File Format (format that your computer can read)

The File Format can include
JPEG
Downsized JPEG
RAW data in the form of a file type (.CR2 (Canon), .NEF (Nikon), .DNG (Adobe Open Source))
Downsized RAW file: Canon cameras have an sRAW mode now

So during the third step, yes, the resolution is always the same. During the file format step, anything can happen.

 

[rookie1010]

thanks for demystifying camera sensors guys