real usage for auto levels?


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superhero

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Apr 24, 2002
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#1
i noticed some people use auto levels for all their pics...

for me , i use it sometimes when i feel the pics is too dark.

but what is its real usage for??
do we always need to use it to assure gd printouts ?? :dunno:
 

roygoh

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Jan 18, 2002
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#2
Auto-level maximizes the dynamic range of the picture. It stretches the histogram of each colour to utilize the entire available range. In the case of 8-bit RGB, it will expand the histograms of each colour to span from 0 to 255, and pic the appropriate centre point.

The effect is generally an increase in contrast, and in some cases more accurate and vibrant colours.

It will not work on all pictures. In pictures where a particular colour dominates, using auto-level will shift the colour too much, making the picture unreal.

The level controls can be seen as a "limited edition" of the curves control. Adjusting levels is the same as adjusting curves but using only straight lines to map the inout values to the output values.

Disclaimer: I am not quoting the qbove from any books or reference text or websites. Just my own understanding.
 

StreetShooter

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Jan 17, 2002
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#3
Auto levels is a quick and dirty way to adjust the histogram and colour balance, as Roy said. Sometimes it works, sometimes it doesn't.

What I do is simply Shft-Ctrl-L, and if I like it, I keep it and maybe tweak a little bit more. If it's totally off and looks unreal, I simply Ctrl-Z and adjust manually.

I find it VERY useful for adjusting colour balance when I convert negatives to digital by using a macro lens and taking a picture of the negative against a fluorescent light box. In fact, I batch process these, doing a simple inversion followed by auto-levels. Sure beats adjusting the colours manually. You can always tweak a little bit more later.
 

roygoh

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#4
I usually apply Auto Levels first, if the results are OK, I will then fine tune it with Curves for more accurate colour and contrast adjustment.

If the Auto-Levels makes things worst, then I will undo that and use only curves.
 

denizenx

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Feb 1, 2002
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#5
it also solves the all-frequent problem of distance haze...

See my example

if you can, click the url above to see... when I shot it the place was having after-rain mist...
 

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