I understand changing shutter speed and/or size of the hole, but what does changing the ISO do in the digital camera? (Page 2): The sensor output is an analog signal. The signal is...

Apaflo Loc: Anchorage, Alaska

GalaxyCat wrote:

Maybe somebody knows, someone in the industry can tell us. I want to know the guts.

The sensor output is an analog signal. The signal is amplified before it goes to the ADC (Analog to Digital Converter). The gain of the amplifier sets the ISO.

Note that only aperture and shutter speed can change exposure. ISO changes how bright the image is, but does not change exposure. Brightness can also be changed by digital multiplication, but that changes bit depth that reduces potential dynamic range too.

Note that the sensitivity to light of the actual sensor cells is fixed and never changes.

mwsilvers Loc: Central New Jersey

Apaflo wrote:

The sensor output is an analog signal. The signal... (show quote)

I have a feeling you're explanation, although correct, is way too technical for the person to whom you were responding.

Apaflo Loc: Anchorage, Alaska

mwsilvers wrote:

I have a feeling you're explanation, although correct, is way too technical for the person to whom you were responding.

It is exactly what was asked for after others tried to use sugar coated false information. Granted it is too technical for many people.

repleo Loc: Boston

GalaxyCat wrote:

I understand changing shutter speed and/or size of the hole, but what does changing the ISO do in the digital camera?

My simplistic understanding is that turning up the ISO is just increasing the amplification of the signal from the sensor.

d3200prime

GalaxyCat wrote:

I understand changing shutter speed and/or size of the hole, but what does changing the ISO do in the digital camera?

Go to www.udemy.com and look up Photography Fundamentals: Understand Aperture, Shutter, ISO+. It's FREE and will teach you much.

PixelStan77 Loc: Vermont/Chicago

GalaxyCat wrote:

I understand changing shutter speed and/or size of the hole, but what does changing the ISO do in the digital camera?

The ISO setting is the sensitivity of the sensor -- in practice the amount of amplification applied to the signal from the pixel on the sensor to get a real result. Tht is what happens inside a digital camera

rmorrison1116 Loc: Near Valley Forge, Pennsylvania

I don't know if anyone has answered the question this way but, changing the ISO is like changing the volume on an amplifier. You turn the ISO down and the amplification of the electrical signal coming from the image sensor is decreased. The lower the setting the less electronic noise. Turn the ISO up and you increase the amplification of the electronic signals coming from the image sensor. Doing this increases the electronic noise. One of the advantages of todays high end processors, like the DIGIC 6 or DIGIC 7 processors in Canon cameras is, the processors are able to recognize electronic noise better than older processors. Being able to tell the difference between good data and unwanted data makes it possible to create cleaner images at higher ISO settings.

TriX Loc: Raleigh, NC

GalaxyCat wrote:

I went to www.nikonusa.com and I still didn't get the real technical answer to this question. How exactly does the camera change the "Sensitivity of the sensor?" Maybe it is proprietary information, but I will keep looking.

There are multiple ways. You can change the gain of the amplifier between the sensor and the A/D converter (as Apaflo mentioned), or you can numerically multiply the output of the A/D in software, or use a combination of the two (as is done in Canon and other cameras). You could also change the reference voltage to the comparator in the A/D, but I’m not aware if any manufacturer uses this method.

Bobspez Loc: Southern NJ, USA

Raising iso = more light + more noise. Try it and see. If lighting is changing quickly, you can set iso to auto and it will let you keep the same aperture and shutter speed in different lighting, like sun and shade.

mwsilvers Loc: Central New Jersey

Bobspez wrote:

Raising iso = more light + more noise. Try it and see. If lighting is changing quickly, you can set iso to auto and it will let you keep the same aperture and shutter speed in different lighting, like sun and shade.

Raising ISO absolutely does not mean more light. Its means in simplistic terms that the sensitivity of the sensor is being amplified, along with any noise. Its an electronic feature of digital cameras that may give the impression of more light but that is not the case. Likewise in film cameras fast film, like ISO 400 or ISO 1000, doesn't increase the light, it increases the sensitivity of the film to the available light.

GalaxyCat Loc: Boston, MA

I can see recording from each pixel the combination of the RED, BLUE, GREEN photo cells. And I can see how gain would affect the brightness and contrast of the individual sensor cell. Therefore, the the setting of the ISO does change the gain of each pixel, and the noise will increase with more gain; then performing an ADC (analog to digital converter) is necessary to make a jpeg or raw file. I get it now. However this may not be exactly how the cameras work. I might be surprised if I search more and more, which I want to do. The changing the ISO could affect some other parameter: like the supply voltage to all the cells. That might be simpler than changing gain in an amplifier. It all depends on the design.

RichardTaylor Loc: Sydney, Australia

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Apaflo Loc: Anchorage, Alaska

GalaxyCat wrote:

I can see recording from each pixel the combinatio... (show quote)

There are no "RED, BLUE, GREEN photo cells" for each pixel. Raw sensor data is not encoded as RGB data, but as Bayer Color Filter Array data. That is a single color at the pixel location with other single colors at adjacent pixel locations.

Virtually all DSLR cameras work that way while absolutely none ever change the sensor supply voltage.

GalaxyCat Loc: Boston, MA

Okay, thanks for the information. Very interesting.

Apaflo wrote:

There are no "RED, BLUE, GREEN photo cells" for each pixel. Raw sensor data is not encoded as RGB data, but as Bayer Color Filter Array data. That is a single color at the pixel location with other single colors at adjacent pixel locations.

Virtually all DSLR cameras work that way while absolutely none ever change the sensor supply voltage.

GalaxyCat Loc: Boston, MA

Thank you so very, very much for the name of the raw sensor data, Bayer Color Filter Array data. I looked it up on google:

A Bayer filter mosaic is a color filter array (CFA) for arranging RGB color filters on a square grid of photosensors. Its particular arrangement of color filters is used in most single-chip digital image sensors used in digital cameras, camcorders, and scanners to create a color image. The filter pattern is 50% green, 25% red and 25% blue, hence is also called BGGR, RGBG,[1][2] GRGB,[3] or RGGB.[4]
It is named after its inventor, Bryce Bayer of Eastman Kodak. Bayer is also known for his recursively defined matrix used in ordered dithering.
Alternatives to the Bayer filter include both various modifications of colors and arrangement and completely different technologies, such as color co-site sampling, the Foveon X3 sensor, the dichroic mirrors or a transparent diffractive-filter array