Aperture Exposure Vs Brightness

Could sombody explain the difference between these?

in general exposure vs brightness is very different.

exposure is a combination of different things/values, and works to keep the levels correct like midpoint (grey), black and white, with good contrast

brightness is just more luminance and shifts all the other values, most of the time killing the contrast

look here at the brightness and exposure details with the histograms:
http://www.scantips.com/bce.html

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Thanks.

So it kind of looks to me like "brightness" in more like the equivalent of an in camera exposure adjustment (Where everything would brighten) and exposure is like this combined with contrast expansion. Does that sound correct?

Steve

Steve Farley said:

Thanks.

So it kind of looks to me like "brightness" in more like the
equivalent of an in camera exposure adjustment (Where everything
would brighten) and exposure is like this combined with contrast
expansion. Does that sound correct?

Click to expand...

I'm not sure that's quite the way to look at it...

It's really good to think about these things in terms of the histogram, and values it holds. Wherever you see hills or peaks on the histogram, that represents some pixels in your image - the closer to the left the darker those pixels are, the closer to the right the brighter. The higher that part of the histogram, the more pixels it represents.

You can think of almost any adjustment as being like stretching a piece of silly-putty. In the case of "Exposure" imagine silly putty attached to a stick. The stick in this case is at the low end of the histogram where the darkest pixels are- exposure only stretches the putty away from the stick, leaving the pixels closest to the stick not moved as much as the part you are stretching out. Negative exposure adjustment compresses the putty and moves all the pixels closer to the left.

"Brightness" is like putty between two sticks. As you move it closer to one end or the other it kind of lumps up and gets thin on the other end.

To take a moment here, that is why Brightness makes things look kind of "washed out" - because the really dark pixels were moved quite a lot over to the lighter side, whereas with Exposure they tend to stay more fixed to the darker side.

Lastly there is Contrast - this is like putting a stick through the middle of the putty and pulling at both ends, with an even stretching across the whole putty.

One last interesting thing to note is that the "middle" of the putty is always defined by where the values are - so if you move the Brightness up then the center of the histogram that would be stretched around for Contrast will move too. As noted before the "sticks" are really were the darkest and brightest pixels lay, so if you have no real "black" pixels then exposure and contrast adjustments will never make anything black either, as they'll stop where the last pixel sits.

Your description then was kind of close, the way it differs is thatan increase in exposure still will move the blacks a little to the lighter side (just not as much as the brighter values get brighter). The combination of Brightness + Contrast can leave the blacks all the way at the end depending on how you adjust it..

One goal in playing with adjustments is (usually) to have a "Full" histogram, with a good balance between blacks and whites. So a good starting point is to play with the histogram controls to stretch the histogram to full the whole space between black and white - then proceed to make other adjustments from there to either make the image generally brighter or darker.

If you want to lump more of the histogram at a particular point, you can use the Levels tool in combination with the quarter-tone sliders - use the middle slider to set a point to "lump" to, then the quarter-tone controls to move regions of the histogram toward (or away from) that central point.

Take an image and play around with the various controls, and think about what is happening to the pixels by looking at both your image and the histogram at the same time. It may be easier to start with a B&W picture as color can confuse the issue (just apply the Monochrome Mixer)

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