Brain teaser #1: Recreating curve settings

PE
Posted By
phoney.email
Oct 25, 2003
Views
580
Replies
6
Status
Closed
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.
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Warren Sarle
Oct 25, 2003
"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.

You might not be able to determine the exact number and placement of knots, but you could come close enough for most practical purposes. Mathematically, it’s just a matter of fitting some splines to the image data. You could do this easily with SAS if SAS could read image files, but I don’t know any easy way to do that. Matlab is pretty good at both math and image processing, so if you have access to Matlab somewhere you might give it a try. There’s a Matlab news group somewhere you could ask about the details.
F
Flycaster
Oct 25, 2003
"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?

Automagically, I don’t think so. But you can get fairly close by making a curve adjustment layer, using the color picker values as references, and then SAVE it..

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PE
phoney.email
Oct 26, 2003
On Sat, 25 Oct 2003 21:08:22 GMT, "Warren Sarle" wrote:

"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.

You might not be able to determine the exact number and placement of knots, but you could come close enough for most practical purposes. Mathematically, it’s just a matter of fitting some splines to the image data. You could do this easily with SAS if SAS could read image files, but I don’t know any easy way to do that. Matlab is pretty good at both math and image processing, so if you have access to Matlab somewhere you might give it a try. There’s a Matlab news group somewhere you could ask about the details.

Yes, that’s exactly what I was thinking. It’s all numbers in the end.

I was just wondering if there was an automagic way to do it in Photoshop e.g. with the difference layer or whatever.

Anyway, thanks!

Don.
PE
phoney.email
Oct 26, 2003
On Sat, 25 Oct 2003 16:51:33 -0700, "Flycaster" wrote:

"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?

Automagically, I don’t think so. But you can get fairly close by making a curve adjustment layer, using the color picker values as references, and then SAVE it..

As I said, it’s not a question of forgetting to save but a theoretical question. I could have a (convoluted) real life application of this.

Anyway, thanks for the tips!

Don.
T
tacitr
Oct 27, 2003
Question:
Given images A and B how do I automagically recreate the curves used?

In Photoshop? You can’t. You have to eyeball it.

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PE
phoney.email
Oct 27, 2003
OK, thanks!

Don.

—

On 27 Oct 2003 02:43:48 GMT, (Tacit) wrote:

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

In Photoshop? You can’t. You have to eyeball it.

—
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