bcrawf

I have a good close-up bellows rig to shoot negatives or slides 1:1 (with my full-frame Canon digital camera), but I need to discover how to convert the image of a color negative to a positive. (I did not find useful comments in search here.) I have strobe flash light for the exposure. Any helpful experience?

rmalarz Loc: Tempe, Arizona

Photograph them as they are. In your processing software, there should be an Invert command. That will do the trick.
--Bob

via the lens Loc: Northern California, near Yosemite NP

Lightroom allows you to do this in the Tone Curve Panel. Just reverse the line in the tone panel histogram. I often do it with photos just to see how they turn out.

burkphoto Loc: High Point, NC

Make the RGB curves look like a back slash (\) instead of a forward slash (/). Then bend them individually and set shadow and highlight points for color correction.

Be patient! It takes a while to get the color right. Every brand, type, speed, and emulsion batch of color negative film is different!

Oh, know that color negs are meant for 3200 K tungsten illumination behind color printing filters. You may need an 85B or Full CTO filter over the flash head...

robertjerl Loc: Corona, California

What PP apps do you have? Some have a command for this, but we need to know which app to tell you where it is and what they call it.

blackest Loc: Ireland

Vuescan isn't bad, old color negatives tend to have changed color over the years and are very hard to fix well.

Here is one manual method invert the curve in lightroom to get a positive with a cyan cast find something grey to set a custom white balance. It will still have a cast as the lowest temperature that lightroom works with is 2000. Go to export as tif with lightroom adjustments to say silverfx and cancel. You just want the tiff file now try for a grey again and it should come in fairly close.

You might just make a preset to invert the negative , export as a 16 bit tiff and then try to color balance that. Save that color balance as a preset and you might be ok with that kind of film. You can also adjust the start and end points of the rgb curves individually... Color negatives pig of a job to balance manually but some of the scanner software does a fair job. flash might not be a great source of light. I'm using an enlarger head and a macro lens myself i'm not too upset with the color balance. Another way for removing the color cast is in photoshop with the match color tool. Getting all the shades of red green and blue correct is pretty difficult. If you are not too OCD acceptable it is possible. Your fighting quite a battle to be fair with the orange mask way more red values are collected than green and blue. Which leaves you with lots of red information and not much blue and green.

If a negative is badly exposed skip it, you will never get a decent scan out of it. It makes sense to only work with the best shots anything badly composed or out of focus isn't worth your time.

Converting to black & white is a reasonable path when faced with a difficult negative.

burkphoto Loc: High Point, NC

All good advice. I’ve had similar experience, based on years in the lab.

Color negative film layers each have a different “slope” to their response curves. If a normal exposure is properly color balanced, an overexposure of the same scene may be light and cyan, while an under exposure may be dark and red.

We had nine $50,000 Kodak Bremson HR500 scanners in our scan room. Setup involved a lengthy process of calibrating offsets for slope, using negatives at +2 to -2 stops away from normal, at 1/2 stop intervals. Once set, the driver software could automatically correct color over that range.

blackest Loc: Ireland

There is good reason why they cost 50,000. An 80a blue filter can help a bit this will tone down the orange and allow a longer exposure which would bring up the detail in the blue and green channels. It may make getting a good color balance that bit harder.

bcrawf

Thanks to several here for the several assists. I am using Photoshop CC. I found the Auto Tone command to be the most help (which was after I inverted the image and got a very blue result which looked as if it were a B/W image with blue toning. I think that is probably the result of the color temperature of my studio strobe. I see the suggestion of using a filter for that. I had a lot of adjusting of color balance to do, but got a pretty good result.

blackest Loc: Ireland

About the lowest color temperature you get with photoshop is 2000 degrees the controls work backwards n an inverted image. if you save a 16bit tiff once the raw file is inverted , that tiff will act like a regular color file and the sliders are all back in the middle position. Photoshop doesn't know the starting values that generated that tif just the values that were saved after inverting.

rook2c4 Loc: Philadelphia, PA USA

Exactly.
As next step, target the area outside of the image frames (which have turned from brownish to bluish by the tone curve reversal in the first step) for white balance adjustment. This will neutralize the blue tint and give you a good starting point for tonal fine-tuning as needed.