Curvemeister Forum

Hello All,

In the past I have scanned several thousand color negatives to 48 bits TIFF images treating them as positives. I used a Minolta Dimage Scan Elite 5400 machine. The reason I didn't use the Minolta software option to scan them as negatives, thus obtaining positive images is that I didn't trust their conversion algorithm. I used Photoshop to do my own conversion, with varying success.

Is there a way to use CM to do the conversion? I have available in nearly every scan a small area of the orange background, and I suspect that using this information, apply the correct gamma and invert the image, this should be possible. But I lack experience with CM to do the "backgroud subtraction" and the conversion. Is there anyone who could help me?

I attach an example (24 bit jpg) reduced to 20% just to illustrate the kind of images I have available.

There is a technique that works reasonably well.  Here is a short summary of the technique:
http://www.curvemeister.com/tutorials/what_ails_you/

I'm heading out the door right now but will try to give your image a try later on.

I'll look at the link you gave tomorrow.
Is it useful to send you the original 48bit Tiff, e.g. as a "WeTransfer" file? That is the kind I want to process.

I had a shot at your image with CM.

Hello Ganna,

Great!
That is exactly as I remember the colors! How did you do it? Please let me in on your secret? Is it difficult? For one I can't find how to invert colors in CM, I had to do it in Photoshop. Lightroom also doesn't have the invert colors function.

Alex, have you done a CM 101 class with Greg? I see there's one coming up soon. Greg will teach you how to do it. I did this in about 4 steps in CM,firstly by moving the diagonal line in the lightness canal of Lab through 90°, so that the lower end is right and upper end left. After that I did a color correction by the numbers firstly through RGB and lastly  a color boost in Lab.

Alex,
I have created a short video which I will be posting out to YouTube and I'll link it back to the forum.
This is a really good question for Curvemeister users.
It is about 4 minutes...

Greg

Everyone,
Here is a link to the Video describing how to make this conversion in Curvemeister.

http://youtu.be/lrIDpLVpqTk

Greg

Ganna: Yes I did the class several years ago. Also I studied the book Photoshop LAB Color by Dan Margulis, but I don't remember seeing anything in it that would be helpful.

I did try to reverse the L-channel line, but the result is disapointing: the image is totally off color. In a different image a bright red cushion shows as a dark green one. I don't see how this could lead to a more natural image. Shouldn't the a and b channels also be inverted?

Greg:
This is really very enlightening, your video. I'll come back when I have tried it a few times on different images. Do you think there could be a library file (.acv) made that does the job for a set of color negatives made under the same conditions?

I am ashamed to say that I have used CM very little these past few years - I have to find out all about it again!

Thanks very much, Greg!