Exposure vs Brightness

[OldClicker]

In post processing (i.e. PS CS4), what is the difference between 'exposure' and 'brightness'? - TIA, TF

[drg]

Brightness is the adjustment in percentage of the amount of light we use/see in the photo image. The is often referred to as perceived luminance. There is a scale of 0(black) to 100(total white) but you will see a Brightness number greater than 100! That is to attain certain affects to blow out an area (such as in high contrast) that is not at the upper edge of the exposure range.

Exposure is 'generally' the amount of light that we try to capture or let fall on the sensor, sort of. It is the overall combined effect of several different measurement including brightness, contrast, lightness and now in the digital age dynamic range.

If you are working in the RAW converter (ACR) notice that there still exists both Brightness and Contrast which are 'left overs' or legacy adjustments from the earliest version of Photoshop RAW implementations. Now with the Exposure tools in CS4 and Lightroom various highlights, shadows, mid-range etc., can be tweaked individual as opposed to dragging the whole histogram right or left to 'brighten' or 'darken' the image. Very similar results in many examples but not all!

These adjustments fall between the physical measured Luminance and Reflectance and the perception of how we see them as quantity with those magic subjective terms of Brightness and Lightness.

Look at different effects displayed on a histogram resulting from individual adjustments an how the 'shape' as well as the 'width' and 'height' of the histogram are altered.

Much of this is from how different photographers think about lighting and exposure and results in some overlapping terms and techniques.

There are a lot of misuses of this terminology in both print, software, and oh my! on the Internet. Some of it is an attempt by the software company or writer of the manual to describe the results of using a very complicated tool with an overly simplified interface as to what it does.

Lightness is a good example of an often misused term as it traditionally is about the reflective quality of a surface. Yet on display it is transmitted light so that doesn't work the same! It, Lightness, too is a perceived quality of what we can physical define and measure as Reflectance. But I digress.

If you want more details let me know and I'll try to clarify or make this more technical.

[Canyon Hiker]

I don't use CS4 but this is what I'm guessing. I would think the "exposure" tool is more of a auto levels tool. It probable stretches out the histogram removing the gap from the histogram. Moving the slider up is making the darkest pixels black and lightest pixels white all while not moving the mid tones. As where the brightness command works globally. That is they affect all pixels in the image equally. Moving the slider up brightens all pixels, and moving the slider down darkens all pixels. Hope that helps some. If anyone has a better explanation please do so.

Darin

[Canyon Hiker]

You beat me to the punch. That's a great explanation drg.

[Medley]

From the Adobe website:

"The Exposure adjustment allows you to produce a linear shift in brightness, where all pixels in the image are brightened or darkened to a similar degree."

"The Brightness slider allows you to adjust the overall brightness of the image, similar to the control provided by the Exposure slider. The only difference is that the Brightness slider will not clip highlights or shadows, but will instead compress the tonal information at the ends of the tonal range as you make adjustments. It is therefor a safer adjustment tool, although it doesn't provide the range offered by the Exposure slider. Think of it as behaving like the middle tone slider in the Levels dialog."

That answer your question?

- Joe U.

[OldClicker]

Thank you all very much. I understand now. - TF