Difference between brightness and exposure?

[magomago]

I'm wondering if someone can explain that - any explanation would greatly help...but I just realized that I couldn't answer it

I know exposure is the total amount of light that falls on the sensor, correct? And this is measured in lux*unit time

so in terms of photo editing I would see adjust exposure as changing, proportionally , the entire exposure. Abstractly and conceptually, if I have a sensor of three boxes with values of 1,2,3 and I adjust the exposure I make it 2,3,4..

Does any of that make sense, or is it even right?

but for brightbness...errrr ummm???

 

[Jawo]

Good Question! Made me inquisitive and from what I have read it seems that brightness is the sum of the RGB colors on the histogram.

Wikipedia

In the RGB color space, brightness can be thought of as the arithmetic mean µ of the Red, Green, and Blue color coordinates[citation needed] (although some of the three components make the light seem brighter than others, which, again, may be compensated by some display systems automatically):

 

[Zenmervolt]

Watch the histogram while you're adjusting brightness and exposure.

Increasing brightness lifts all values equally.
Increasing exposure lowers the point at which the highlights begin to clip.

That's why you can only truly adjust exposure with RAW files. A JPG is an 8-bit image format (that is, each color channel can have 8 bits of information for a total bit depth of 24 bit), but most cameras with RAW capabilities can record 12-bit RAW data. That means there is additional data in the RAW file that cannot be encoded into a JPG image. Adjusting the exposure changes where the minimum and maximum values are assigned.

Think of it this way:

Total RAW file data ("B" for pure black, "W" for pure white):
B--------------W

Total JPG data:

B-----W

The JPG data must overlap the RAW data, but it can overlap it at any point. Adjusting the exposure moves the points at which the JPG overlaps the RAW. So, if we take the examples above with "B" and "W" being black and white for RAW and "b" and "w" being black and white for the JPG we end up with the JPG representing something like this:

B--b-----w-----W

The values below the "b" and above the "w" are dropped from the JPG image data and the "b" point becomes pure black and the "w" point becomes pure white. Increasing the exposure could give us:

B----b-----w---W

In this second case, the JPG will have more highlight information, but the shadows will drop to black faster.

Brightness just increases the values across the board without changing the data that are represented in the image.

This means that it's brightness that changes values from "1,2,3" to "2,3,4". Exposure adjusts how the minimum and maximum points are determined for the overall image.

(I think.)

ZV