Brain teaser #1: Recreating curve settings

Given this:
1. Take an image (let's call it image A).
2. Apply some curve settings to it.
3. Save this modified image (let's call it... oh I dunno... image B?).
4. Forget what curve settings were used.

Question:
Given images A and B how do I automagically recreate the curves used?

Yes, yes, I know... I can save curves, but that's not the point.

Thanks in advance.

Don.

P.S. If that's too hard, replace curves in the question above with something linear like levels.

Record the action and assign a key to it.. let's say F9.

No math needed.

"Don" wrote in message

Given this:
1. Take an image (let's call it image A).
2. Apply some curve settings to it.
3. Save this modified image (let's call it... oh I dunno... image B?).
4. Forget what curve settings were used.

Question:
Given images A and B how do I automagically recreate the curves used?
Yes, yes, I know... I can save curves, but that's not the point.
Thanks in advance.

Don.

P.S. If that's too hard, replace curves in the question above with something linear like levels.

Don wrote:

Given this:
1. Take an image (let's call it image A).
2. Apply some curve settings to it.
3. Save this modified image (let's call it... oh I dunno... image B?).
4. Forget what curve settings were used.

Question:
Given images A and B how do I automagically recreate the curves used?

An interesting question. I don't think there's an automatic way to do it. but it could be done by manually adjusting a curves layer.

I'd start by dragging image B onto image A as a new layer, and setting the layer mode to subtract mode. Then group a curves layer over image A, and fiddle with each channel in turn (click on the eye icon for that channel in the channels pallete to show only that channel) until you are as close as possible to a black image.

The most important points to get right are the end points of the curve, followed by the middle and quarter and three quarter tones.

--

Mike Russell
http://www.curvemeister.com
http://www.zocalo.net/~mgr
http://geigy.2y.net

In article ,
(Don) wrote:

Given this:
1. Take an image (let's call it image A).
2. Apply some curve settings to it.
3. Save this modified image (let's call it... oh I dunno... image B?).
4. Forget what curve settings were used.

Question:
Given images A and B how do I automagically recreate the curves used?
Yes, yes, I know... I can save curves, but that's not the point.
Thanks in advance.

Don.

P.S. If that's too hard, replace curves in the question above with something linear like levels.

Hold down option (if you're on a Mac) when selecting Curves from the menu. This works with Levels, Brightness and Contrast, and others...

Jim

-------------------------------------------------------

pester me, why not? whokid at flywheelnetwork . co . uk

Like I said in my original email, it's not a question of saving but a theoretical question (with a possible real life application).

Don.

Record the action and assign a key to it.. let's say F9.
No math needed.

"Don" wrote in message

Given this:
1. Take an image (let's call it image A).
2. Apply some curve settings to it.
3. Save this modified image (let's call it... oh I dunno... image B?).
4. Forget what curve settings were used.

Question:
Given images A and B how do I automagically recreate the curves used?
Yes, yes, I know... I can save curves, but that's not the point.
Thanks in advance.

Don.

P.S. If that's too hard, replace curves in the question above with something linear like levels.

On Sat, 25 Oct 2003 22:00:12 GMT, "Mike Russell" wrote:

Don wrote:

Given this:
1. Take an image (let's call it image A).
2. Apply some curve settings to it.
3. Save this modified image (let's call it... oh I dunno... image B?).
4. Forget what curve settings were used.

Question:
Given images A and B how do I automagically recreate the curves used?

An interesting question. I don't think there's an automatic way to do it. but it could be done by manually adjusting a curves layer.
I'd start by dragging image B onto image A as a new layer, and setting the layer mode to subtract mode. Then group a curves layer over image A, and fiddle with each channel in turn (click on the eye icon for that channel in the channels pallete to show only that channel) until you are as close as possible to a black image.

The most important points to get right are the end points of the curve, followed by the middle and quarter and three quarter tones.

Thanks, Mike!

As always, you read the question carefully and come up with exactly the answer I'm looking for!

Don.

On Sun, 26 Oct 2003 01:45:26 +0000, Whokid
wrote:

In article ,
(Don) wrote:

Given this:
1. Take an image (let's call it image A).
2. Apply some curve settings to it.
3. Save this modified image (let's call it... oh I dunno... image B?).
4. Forget what curve settings were used.

Question:
Given images A and B how do I automagically recreate the curves used?
Yes, yes, I know... I can save curves, but that's not the point.
Thanks in advance.

Don.

P.S. If that's too hard, replace curves in the question above with something linear like levels.

Hold down option (if you're on a Mac) when selecting Curves from the menu. This works with Levels, Brightness and Contrast, and others...
Jim

I'm on Windows so it's the Alternate key, but I'm not quite sure what you mean. Could you please outline it step by step. Thanks!

Don.

In article ,
(Don) wrote:

I'm on Windows so it's the Alternate key, but I'm not quite sure what you mean. Could you please outline it step by step. Thanks!

Don,

I don't know if this works on PC as I am alergic to Windoze, so you'll have to just try it with the [Alt] or [Control] keys...

On "Image 1" go to Curves as normal, make some settings and apply them.

Then on "Image 2" go back to the menu, hold down [Alt or Control] and use the mouse to bring up Curves again. If there is a God, your previous settings should still be there.

It works on a Mac, I've just checked. It also works with most items in that menu, including Levels, B&C, Hue Sat and so on.

HTH.

Now I think about it, there is a keyboard shortcut for this, which I also just tested:

[Command]+[M] = Curves dialogue
[Command]+[Option]+[M] = Curves dialogue with previous settings

Just experiment with it. The worst that can happen is that you'll wipe the internet. ;o)

Jim

-------------------------------------------------------

pester me, why not? whokid at flywheelnetwork . co . uk

On Sun, 26 Oct 2003 18:51:29 +0000, Whokid
wrote:

In article ,
(Don) wrote:

I'm on Windows so it's the Alternate key, but I'm not quite sure what you mean. Could you please outline it step by step. Thanks!

Don,

I don't know if this works on PC as I am alergic to Windoze, so you'll have to just try it with the [Alt] or [Control] keys...

Oh, believe me, I'm no friend of the evil empire or His Billness. But, then again, I also have issues with His Holiness Steve the Second. ;o)

On "Image 1" go to Curves as normal, make some settings and apply them.
Then on "Image 2" go back to the menu, hold down [Alt or Control] and use the mouse to bring up Curves again. If there is a God, your previous settings should still be there.

OK, now I get it! I was actually asking something a little different, but this is a very good tip to know! Thanks!

Just experiment with it. The worst that can happen is that you'll wipe the internet. ;o)

Well, that's one way to get rid of spam? ;o)

But seriuosly, thanks very much, Jim!

Don.

Could this also be done also by observing the histogram for each image. Again setting the end points as best as possible, then adjusting midtone while observing the pixel count at a significant point or points in the curve. (for each channel)
The difficulty of the task would increase should there be much clipping at either end of the curve.

"Mike Russell" wrote in message

Don wrote:

Given this:
1. Take an image (let's call it image A).
2. Apply some curve settings to it.
3. Save this modified image (let's call it... oh I dunno... image B?).
4. Forget what curve settings were used.

Question:
Given images A and B how do I automagically recreate the curves used?

An interesting question. I don't think there's an automatic way to do it. but it could be done by manually adjusting a curves layer.
I'd start by dragging image B onto image A as a new layer, and setting the layer mode to subtract mode. Then group a curves layer over image A, and fiddle with each channel in turn (click on the eye icon for that channel

in

the channels pallete to show only that channel) until you are as close as possible to a black image.

The most important points to get right are the end points of the curve, followed by the middle and quarter and three quarter tones.
--

Mike Russell
http://www.curvemeister.com
http://www.zocalo.net/~mgr
http://geigy.2y.net

mitch wrote:

Could this also be done also by observing the histogram for each image. Again setting the end points as best as possible, then adjusting midtone while observing the pixel count at a significant point or points in the curve. (for each channel)
The difficulty of the task would increase should there be much clipping at either end of the curve.

Absolutely - although the histogram is limited only to levels and not curves, this would work very well.

I don't think the clipping issue is important for most images, but it could be a problem if only a small subset of the image were retained. This is another of many examples of how looking at the histogram can give the wrong impression of what needs to be done. Looking at the image will give a better idea of what's happening overall.

--

Mike Russell
http://www.curvemeister.com
http://www.zocalo.net/~mgr
http://geigy.2y.net

"Whokid" wrote in message

I don't know if this works on PC as I am alergic to Windoze, so you'll have to just try it with the [Alt] or [Control] keys...

On "Image 1" go to Curves as normal, make some settings and apply them.
Then on "Image 2" go back to the menu, hold down [Alt or Control] and use the mouse to bring up Curves again. If there is a God, your previous settings should still be there.

It works on a Mac, I've just checked. It also works with most items in that menu, including Levels, B&C, Hue Sat and so on.
HTH.

Now I think about it, there is a keyboard shortcut for this, which I also just tested:

[Command]+[M] = Curves dialogue
[Command]+[Option]+[M] = Curves dialogue with previous settings
Just experiment with it. The worst that can happen is that you'll wipe the internet. ;o)

Jim

Damn! That works a treat. I never knew... (bowing in awe) ;)

Learn a new trick every day I always say, that way you'll never be an old dog.

Thanks.

Tom

In article <VVgnb.43099$>,
"Tom" wrote:

Damn! That works a treat. I never knew... (bowing in awe) ;)
Learn a new trick every day I always say, that way you'll never be an old dog.

Thanks.

Glad to be of help, Don and Tom.

:o)

Jim

-------------------------------------------------------

pester me, why not? whokid at flywheelnetwork . co . uk