Using auto contast verses histogram sliders – which is best?

IW
Posted By
ID_Williams
Mar 2, 2004
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167
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4
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Closed
Hello,

Is it better to use auto contrast or the histogram sliders on an image that requires slight darkening? I have observed that both techniques seem to produce the same result.

If you use the histogram sliders, what is the correct method of using the sliders?

I do the following:

1. Look at the histogram and note how much area is to the left or right of the main histogram. If there is room for slider adjustment, I;

2. Then using the left side middle triangle I move it to where the histogram begins to start. I may do the same for the right middle slider as well. (this seems to produce the same result as auto contrast?)

Is this the correct way???

Does moving the slider do the same as auto contrast?

Many thanks………….Iain
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SS
Susan_S.
Mar 2, 2004
Yes, auto contrast works in pretty much this way – taking the endpoints of the (composite) histogram and setting them as black and white (auto levels does the same with the three R, G, B channels separately) – you can choose values other than pure black and white for the endpoints by double clicking on the eyedroppers in teh levels dialogue box.

However for an image that is different than the average this may not be appropriate – in a high key image for example you may not want to force the darks to be that close to black, but keep the image tone lighter. Similarly in a deliberately dark image – silhouettes at sunset, for example – you may well not want to have the lightest tone all the way up to pure white. in these cases you may well want to do things manually.
Susan S
IW
ID_Williams
Mar 3, 2004
Thanks Susan – It seems that it really depends on the image. Auto contrasting most images will do fine, but others may require more individual slider adjustment within the levels box.

I take it then that what I am doing with regard to the sliders is correct then – using the left middle and right middle triangles only?

Cheers………….Iain
SS
Susan_S.
Mar 3, 2004
Iain – If you mean what I thought you meant which is the sliders on the bottom of the input levels box – then they are the main ones to use. If you want to overall darken or lighten the average brightness of the image you can use the centre slider too.

Anyone know what the bottom (output level) sliders are good for? (I know what they do – I just can’t think of what I’d use it for….)

Susan S
IW
ID_Williams
Mar 3, 2004
Susan, Yes this is what I meant – the sliders directly under the histogram, but above the output levels. Thanks for your help. I’m about to spent considerable time redoing my images and I want to ensure I do them correctly the first time around.

On another note, I solved my gamma and colour hassles by buying an Eye-One which creates a ICC profile. Thanks again………Iain

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