Auto Levels vs Auto in Levels

[Val Patel]

Hi,

I'm using Photoshop 7.0.1. Why do I get different results when using Auto Levels vs going to Levels and using AUTO? Is there a way to set it up so that identical results are achieved?

Thanks,

Val Patel

[YrbkMgr]

How do you know you are getting different results? The levels dialog gives you access to what is used in AL; they can't be different.

[Madsen]

Val Patel wrote:

> I'm using Photoshop 7.0.1. Why do I get different results when
> using Auto Levels vs going to Levels and using AUTO?

It could be that your Auto button in Levels is set to something
other than Auto Levels. It's possible to do that but the default
setting is Auto Levels when you press the Auto button in Levels
(or in Curves).

> Is there a way to set it up so that identical results are
> achieved?

What happens if you press the Options button in Levels or in
Curves? The algoritm should be 'Enhance Per Channel Contrast'
(which is the same as Auto Levels).

Black: R=0, G=0, B=0.
Midtones: R=128, G=128, B=128.
Highlights: R=255, G=255, B=255.

The shadows should be set to 'Clip 0.50 %' and the highlights
should be set to 'Clip 0.50 %' also.

Maybe you have changed those default settings to something else?

--
Regards
Madsen.

[Colin Walls]

I tried this very carefully. I took a reasonable image and wound down the brightness lots, then duplicated. On one copy I did Auto Levels on the other Levels, Auto. If there's a difference, I'm darned if I can find it. Choosing a couple of spots and zooming in really close [600%], the actual pixels look identical.

So, I'd rephrase Tony's question: what makes you think they're different?

[YrbkMgr]

Even though you didn't even acknowledge me, I thought I'd help anyway.

Options by selecting Find Dark & Light Colors and Snap Neutral Midtones.




That's AutoColor, not Auto Levels.

[Madsen]

Val Patel wrote:

> I changed the Options by selecting Find Dark & Light Colors and
> Snap Neutral Midtones.

If you choose Image > Adjust > Auto Levels, Auto Levels is what you
get, but if you press the Auto button inside the Levels or the Curves
dialog box, you'll get Auto Color, because you've changed it to Auto
Color by selecting 'Find Dark & Light Colors'.

--
Regards
Madsen.

[YrbkMgr]

I'm invisible. I give.

[Madsen]

YrbkMgr wrote:

> I'm invisible.

I can see you. :)

--
Regards
Madsen.

[Val Patel]

Thank you all (YrbkMgr, I'm sorry for not mentioning your name in my first reply) for your replies. Are any of the you using the settings I'm using (from Scott Kelby's book)? What settings give you the best results? Please let me know.

Regards,

Val

[Stroker]

I believe
Image > Adjust > Auto Levels
works on the composite.

While
Image > Adjust > Levels > Auto
works on the seperate R, G, and B channels.

I think that's the case.
Shouldn't be too hard to verify or debunk with some help from Histogram.

edit:
I just did some testing and I'm not getting any difference between the two. Originally I did, but I was using sloppy selections. Once I cleaned up my act, I got the exact same results with both methods.

Copy photo.
On one layer, Image > Ajust > Auto Levels.
On the copy, Image > Ajust > Levels > Auto.
Set the top layer to Difference and you should be looking at pure black.
I did this several times with various photos and I got pure black every time.

[Val Patel]

Stroker,

I'm glad to hear that you see no difference. Can you please tell me what settings you have in OPtions and Eyedroppers when you go in Levels or Curves?

Thanks,

Val

[Val Patel]

Hi,

Is there a way to change the settings of Auto Levels and Auto Contrast and Auto Color individually?

Thanks,

Val

[Stroker]

Val, all of my stuff is default. At least they should be.
Let's see...

Algorithm = Enchance Per Channel
Snap Neutral Midtones = no
Clip/Clip = 0.5%

Eye Colour Dropper Picker Dohickies and Shadows/Midtones/Highlights:
Black = 0,0,0
Gray = 128,128,128
White = 255,255,255

On the rare occassion that I change the colour points, I *always* make it a point to change them back as soon as I'm done. I've banged my head too many times because I changed them and then forgot. You know, along the lines of hitting ctrl + h and forgetting about the selection.

[Val Patel]

Stroker,

Is there a way to reset all these to original default values?

Thanks,

Val

[dave milbut]

it's in the manual val. try f1. i harly ever use it or i'd tell you right out, but i know i've seen it in there...

[Stroker]

I just do it manually.
Maybe someday I'll look for the shortcut that Dave mentioned.

[Madsen]

Val Patel wrote:

> Is there a way to reset all these to original default values?

I guess that you have to trash the preference file if you want to
reset those settings.

--
Regards
Madsen.

[YrbkMgr]

Or set them to the defaults listed in the earler post. You change values, apply them to the image, and you are promted if you want to use the new values as the default.

[dave milbut]

click options in the levels or curves dialog. to reset to default, hold the alt key. it changes the cancel key to reset. sheesh!

[Madsen]

dave milbut wrote:

> click options in the levels or curves dialog. to reset to default,
> hold the alt key. it changes the cancel key to reset. sheesh!

As far as I can see, it changes the settings that you have applied
to the histogram inside Levels, but it doesn't reset the settings
behind the Options button inside Levels to the default.

--
Regards
Madsen.