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Author Topic: Exposure vs. Brightness  (Read 2471 times)
Wayne Lorentz
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« on: March 18, 2007, 11:49:19 PM »
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Sorry if this isn't in quite the right subforum, but it seemed the closest place.

When opening my raw files in Adobe, I am given the option to adjust the image's brightness and exposure (among other things).  Can someone explain to me the benefits of using one technique compared to the other.  To my eye they both achieve the same thing.
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Hermie
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« Reply #1 on: March 19, 2007, 02:02:08 AM »
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In a thread on the Adobe ACR forum the late Bruce Fraser wrote:

"When you boost exposure, you're stretching the entire tonal range.
When you boost brightness, you're stretching the tonal range between the shadow and the midtone, and compressing the tonal range between the midtone and highlight.

Because cameras capture photons linearly (they don't have the compressive nonlinearity offered by eyeballs or film), you have a great deal more data in the midtone-to-highlight range than you do in the midtone to shadow range.

So boosting exposure and lowering brightness stretches the data-rich highlight range and forces more bits into the three-quarter and shadow regions, where you need them. Leaving exposure alone and increasing brightness stretches the relatively data-poor shadow to midtone range, increasing the likelihood of posterization, and making shadow noise more obvious."
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61Dynamic
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« Reply #2 on: March 19, 2007, 10:35:41 AM »
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To add to that, Exposure is your white-point adjustment and will clip highlights. Brightness will not cause clipping up to a point. Any value past 90 will compress highlights so much they are effectively clipped in most cases.

In Lightroom the Brightness and Contrast sliders are there for legacy reasons. The better tool for brightness and contrast adjustment is the tone curve.
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seanmcfoto
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« Reply #3 on: March 20, 2007, 11:11:03 PM »
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Quote
To add to that, Exposure is your white-point adjustment and will clip highlights. Brightness will not cause clipping up to a point. Any value past 90 will compress highlights so much they are effectively clipped in most cases.

In Lightroom the Brightness and Contrast sliders are there for legacy reasons. The better tool for brightness and contrast adjustment is the tone curve.
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An interesting point made by Steve Newbury (doing the Lightroom Demo) at Focus on Imaging was that the Brightness/Contrast in Lightroom is different to Photoshop and is actually being added to PS CS3.
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Phuong
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« Reply #4 on: March 21, 2007, 04:58:27 AM »
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to put it simple think of Shadows as the black slider, Brightness as the grey slider and Exposure as the white slider in the Levels dialog box.
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