Lightroom: Exposure vs Brightness
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rattymouse
Registered: Feb 04, 2006
Total Posts: 4929
Country: China

What is the difference between the exposure slider and the brightness slider? I have to admit, I dont see any! Seems odd.






paulhodson
Registered: Jul 22, 2003
Total Posts: 14361
Country: United Kingdom

If you are familiar with levels in Photoshop the exposure slider is analogous to the right hand arrow and the brightness slider to the centre arrow.

Hence you use the Exposure slider to set the "brightness" of the highlights to avoid them clipping and the Brightness slider to set the "brightness" of the mid tones without affecting the highlights.

Similarly the Blacks slider is like the left hand levels slider in levels and should be used to darken the shadows until just before you lose detail in them.

This is necessarily only a summary - Google for more help or sign on for video training at Lynda.com ($25 per month) for some excellent much needed tuition.



rattymouse
Registered: Feb 04, 2006
Total Posts: 4929
Country: China

paulhodson wrote:
If you are familiar with levels in Photoshop the exposure slider is analogous to the right hand arrow and the brightness slider to the centre arrow.

Hence you use the Exposure slider to set the "brightness" of the highlights to avoid them clipping and the Brightness slider to set the "brightness" of the mid tones without affecting the highlights.

Similarly the Blacks slider is like the left hand levels slider in levels and should be used to darken the shadows until just before you lose detail in them.

This is necessarily only a summary - Google for more help or sign on for video training at Lynda.com ($25 per month) for some excellent much needed tuition.


Thanks for your help. I think I got it now. Using the brightness slider, I cant blow out the highlights, no matter how much I boost it up. With the exposure slider, it is very easy to blow out highlights.

Thanks.






simdoc1
Registered: Sep 26, 2008
Total Posts: 1877
Country: United States

If this is the correct explanation for Exposure, Blacks, and Brightness, what is the relationship between this group and the Tone Curve? Especially with Brightness, it seems as though more subtle changes can be made with the Tone Curve, even if you have made both Exposure and Blacks adjustments.



ohenry
Registered: Nov 13, 2003
Total Posts: 971
Country: United States

The tone curve allows you to specifically alter specific points on the curve. The brightness slider affects the tones on a more global level. If you picked the midpoint on the tone curve and pulled straight up, you'd get similar results as if you slid the brightness slider to the right.



rattymouse
Registered: Feb 04, 2006
Total Posts: 4929
Country: China

ohenry wrote:
The tone curve allows you to specifically alter specific points on the curve. The brightness slider affects the tones on a more global level. If you picked the midpoint on the tone curve and pulled straight up, you'd get similar results as if you slid the brightness slider to the right.


So you can ignore brightness and black slider and do all work using the tone curve. Very interesting. I have learned a lot here.

Thanks again.




ohenry
Registered: Nov 13, 2003
Total Posts: 971
Country: United States

Technically, I suppose you could ignore the sliders and do it from the tone curve, but the sliders are much easier to use when initially adjusting the dynamic range of your image. I don't mess that much with brightness and never use the contrast slider, adjusting specific points using the tone curves. Contrast is best controlled with curves IMO.

I think Ben Long gives a pretty good overview of how he adjusts exposure in this tutorial.



theSuede
Registered: Jul 31, 2008
Total Posts: 2270
Country: Sweden

The main difference between the sliders and the "curves" section is that the curves are applied equally to all three channels AFTER the clarity/vibrance/saturation adjustments are done, and this changes the way very dark and very bright areas in the final outcome are saturated. The difference is not big, but very useful if you learn which of them is effective for different types of pictures... Sometimes you WANT saturation all the way out to black and white (this will blow individual channels), sometimes you want saturation to fade as you approach the luminance endpoints - this gives a more "film-like" but less "superclear and in-your-face" boldness. Sometimes you want one, sometimes you want the other.

All adjustments in the right pane of the "develop" section are executed on the picture in the way they are ordered, from top down. The exception to this rule is the "calibration" part - it is of course executed first-in-line, but [my guess] would be that as it is expected to be used (changed) very seldomly, it is placed last to make the pane less "cluttered".



rattymouse
Registered: Feb 04, 2006
Total Posts: 4929
Country: China

theSuede wrote:
The main difference between the sliders and the "curves" section is that the curves are applied equally to all three channels AFTER the clarity/vibrance/saturation adjustments are done, and this changes the way very dark and very bright areas in the final outcome are saturated. The difference is not big, but very useful if you learn which of them is effective for different types of pictures... Sometimes you WANT saturation all the way out to black and white (this will blow individual channels), sometimes you want saturation to fade as you approach the luminance endpoints - this gives a more "film-like" but less "superclear and in-your-face" boldness. Sometimes you want one, sometimes you want the other.

All adjustments in the right pane of the "develop" section are executed on the picture in the way they are ordered, from top down. The exception to this rule is the "calibration" part - it is of course executed first-in-line, but [my guess] would be that as it is expected to be used (changed) very seldomly, it is placed last to make the pane less "cluttered".


Very very interesting. Thank you for your post. Would you happen to have any examples of this from your past work?



theSuede
Registered: Jul 31, 2008
Total Posts: 2270
Country: Sweden

The best I could find without spending to much time on it was a quickie portrait of my GF and her dog, but I think it illustrates the difference quite well. What we're looking for here is colour shifts when luminance varies.

I want the white backdrop and the black knitting fabric in her cap/cardigan to be neutral (this locks my WB point), and the rest to be quite saturated, but preferably without casts or shifts in colour. The saturation should be EVEN, so that the face doesn't look "blotchy" even if the colour is cranked way up.

My whitebalance is exactly the same in both pictures, and the clarity/vibrance/saturation too. The difference is all due to the curve being shifted before/after the saturation is modified... The difference is fairly subtle, and the flickr recompression sRGB doesn't help the case either, so I suggest you download the pictures and swap between them in your picture-viewer of choice if you can't spot it. First out: normal processing.

1. in the first example this section is left fairly "normal", almost standard settings.
2. Crank the saturation a bit to exaggerate differences later.
3. The grey histogram in this box is what the first three sections (WB, tone and prescence in the "basic" part of the pane) leaves after they've done their work.
4. And then the "curves" go to work on the grey histogram in (3.). Here, no change.
5. This, the top histogram shows what the final produce is, after passing "Tone Curve", "HSL", "Split Toning", "Detail" and "Vignettes. This is delivered to the output section of LR to be converted into your chosen output ColourSpace and maybe output sharpening and resizing before export.



Then all over again, but this time I first compress the picture a bit (lower contrast and exposure, higher brightness) before adding the same amount of saturation. Then i use an S shape in the curves section to shape the histogram back to fairy normal (the grey histogram in (3.) is noticeably narrower than in the first example). Note that the final histogram in (5.) look almost the same as in the first example. Note also that the partly yellow/orange cast in the face is gone even if I haven't touched the WB or colour controls. The shadowy part of the face, and the nose on the dog also shows another hue than the "normal" processing.
The important thing is that the differences between the two pictures are almost entirely in how the saturated areas behave, the dark knit, the backdrop and the grey parts of the dog's nose is almost identical.



rattymouse
Registered: Feb 04, 2006
Total Posts: 4929
Country: China

Thank you VERY much for the incredible example. Fantastic portrait by the way.

What I came away from after reading your post is this line: "What we're looking for here is colour shifts when luminance varies."

This is something I am not too familiar with and need to study further. If I understand this, I think the concept you are demonstrating will make very good sense. Can you say exactly what type of shifts I should be looking for? I guess I am struggling with definitions.




theSuede
Registered: Jul 31, 2008
Total Posts: 2270
Country: Sweden

One not so good thing with LR is that it tries to keep colours saturated all the way into high brightness (white) and low brightness (black) - That's what I mean by saying that the colour shifts with luminance - maybe a more correct way is to say that saturation (how strong the colour is) changes with luminance. But if you clip individual channels you also get colour shifts as the other two channels are quite limited in what hues they can create - you need all three channels to create full colour.

If you're working with a "s" shape on the "Tone Curve" section and lower contrast in the "basic" section you are actually increasing saturation in the areas where the line in the curve is steeper >45 (in the middle) and lowering saturation where the line is less steep <45 (lying down, towards the endpoints).
Pretty simple if you think about it Saturation = how strong a colour is = difference between the RGB colour values. If all three values for R,G and B are equal you get grey. If they're different from each other you get a colour. A steep line separate values more, a flat line compress values together. 45 is linear, what goes in goes out the same way, no separation or compression.

This gives saturation in the medium luminance levels (the middle of the histogram), where they matter, and takes away saturation from very bright or very dark areas - and this is also how our eyes work.

I'm sorry, but I can't think of an easier way to explain this... To get a grip about how the effect works you need to understand why it works.