Convert from Levels to Curves

[J Isner]

Does Photoshop CC have a feature that lets you convert a Levels adjustment layer (or a Levels adjustment) to a Curve?  I seem to remember such a feature in an old version of Photoshop, but I cannot find it in Photoshop CC. 

Such a feature would have tremendous educational value for the course I'm teaching because most students don't understand how the two adjustments are related. It would also have practical value, since you may want to tweak a Levels adjustment (layer) in a way that is only possible in Curves.  Naturally there is no way to go back to Levels from Curves!

If the feature does not exist, I will post it as a feature request.

[JJMack]

Turn off the visibility of the Levels adjustment layer and add a curve adjustment layer.  They work differently IMO  one can not be converted to the other.  While a curves adjustment adjust images levels it  can adjust levels differently then levels not evenly across the image like levels.  A Curve adjustment can adjust levels like the levels adjustment when it applies the levels without using a curve its default diagonal line a linear adjustment.

[J Isner]

I understand how to achieve the effect of a given Levels adjustment using Curves.   What I asked about is whether an automatic conversion from Levels to Curves exists in Photoshop CC.

I respectfully disagree with two of your statements.

• Levels CAN always be converted to Curves (but not vice versa)
• Dragging the midtone slider in Levels produces a non-linear curve.

For example...

is equivalent to

[JJMack]

I can not believe can make a level adjustment that is like every curve adjustment that can be made. equivalent to any curves Curves  can be very complex.

[J Isner]

I never claimed you could convert Curves to Levels.  You can't!   But you can ALWAYS convert Levels to Curves.

[Benjamin Root]

I'm not aware of any such feature. Instead, why not:

• Add a Levels adjustment, set White and Black points to value
• Ctrl + Alt + Shift + E to Stamp visible.
• Move new layer to down below all others.
• Make a Curves adjustment, set White and Black points to Levels' values.
• Stamp visible
• Bring the Levels stamp visible layer up, one below Curves' Stamp visible.
• Toggle top layer's visibility on/off to demonstrate both are identical.

[J Isner]

I'm not interested in how to do it.  I know how to do it.  I'm interested in a feature that does it automatically.  As I said in the OP, such a feature would have pedagogical value, but probably not much practical value.

[Terri Stevens]

I like your idea, but as Benjamin says it doesn't exist in Photoshop and probably for good reasons. What you are asking is for 3 parameters to somehow be converted to 25 (or whatever the max current number of curves points is). How can an algorithm decide that distribution of values beyond the black and white point? I think students should be taught the significance of input and output values and understand digital imagery that way. If you just give them an easy button to press they still won't have a clue as to what is really going on.

[J Isner]

Levels has only 5 parameters.  With these 5 parameters, an equivalent curve can always be constructed.  See my example screenshot above. 

As you say, Curves have at least 5 parameters (one additional parameter for each point added), which is why you aren't guaranteed to be able to convert in the other direction.

And for the umpteenth time, I am not interested in "an easy way" to convert one to the other!  I am looking for something that would be useful in teaching students the relationship between Levels and Curves.  It is a relationship that most Photoshop users (not just students) simply do not understand.

If the feature does not exist in Photoshop for "good reasons," I'd like to know what those reasons are.  The only good reason I can think of is that PS developers don't think it's a useful feature -- and they're right: It's not very useful!  But they could easily implement it if they wanted to.  As I said my OP, I have a vague memory that the feature existed at one time.

[Ronald Keller]

I have had Photoshop since version 2.5. That feature never existed...

[J Isner]

You're right.  It was never in Photoshop.  I just realized that it was in Gimp!  I used Gimp for several years before switching to Photoshop.

As you can see in the screenshot below, the Gimp Levels panel has the same 5 parameters as in Photoshop.  If you click the "Edit these Settings as Curves" button, you'll get the Curves panel with the Levels parameters applied.  I guess I should be teaching Photoshop using Gimp!

[Trevor.Dennis]

You could place two instances in the same document, and mask off one for curves and the other for levels.  Make some adjustments to the curves properties first, and see if you can duplicate the other instance with the levels layer.  The answer is that you can't, or course, but it would demonstrate the differences and limitations of Levels.

[J Isner]

Please read my post more carefully.  You can always create the equivalent Curves adjustment from a given Levels adjustment.  Your example brilliantly demonstrates my point that the conversion cannot be done in the other direction.

[JJMack]

Please show me a levels adjustment like this curves adjustment.

[J Isner]

I never claimed you could convert Curves to Levels.  You can't!   But you can ALWAYS convert Levels to Curves.

[Benjamin Root]

Understood. If you'd like to submit a feature request, you can do so at: feedback.photoshop.com

[J Isner]

Feedback posted.

Thanks to everyone for participating in this discussion.

[JJMack]

OK Yes A cuve like an level adjustmemt is posible but since you can add these adjutment layers why would you want to convert a level adjustment you made to a curves adjustment. Why is there a need to?

[Jeff Arola · Accepted solution]

In photoshop you could use this script to generate a curves adjustment layer from a levels adjustment layer, save out the generated curves because the script creates a separate document with the curves layer and then open a curves adjustment layer in your original and load the saved curves layer.

You could also just duplicate the generated curves layer to your original document.

Not as fast or straight foreword as Gimp, but it does work.

http://www.tonton-pixel.com/blog/scripts/creative-scripts/combine-adjustment-layers/

[J Isner]

That is an amazing script!  I installed it and it works.  For my purposes this will do just fine.   Thanks for posting!