How can I avoid red-channel clipping when DSLR-scanning color negatives?
Asked 10/19/2015
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I’m digitizing color negative film with a DSLR and having trouble getting clean inversions because the red channel clips easily before I even invert the image.
Current setup: Nikon D810, 100mm Tokina macro, copy stand, LED light pad, enlarger film carrier, RAW capture, custom white balance around 2900K. My workflow is to photograph the negative, use an unexposed film leader from the same roll to help neutralize the orange mask, then invert and adjust levels/curves in Photoshop.
The main issue is exposure: to keep the red channel from clipping, I have to underexpose the capture significantly. Some negatives convert much better than others, and denser orange masks seem harder to handle.
Is there a better way to balance the RGB channels before capture so the red channel doesn’t get compressed or clipped? Would filtration at the light source help, and if so what kind? Also, is using an enlarger with a color head a better approach for DSLR scanning color negatives?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
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I filter the orange cast of the color negatives via the light box so that the red channel on the D810 camera I use is not shifted and compressed using 3 sets of gels. My light box is powered with two SB700 flash units and a CFL bulb for focus and composition. I have described my setup twice on this forum before. Here are the gels I use.
Cinegel #3202: Full Blue (CTB),
Cinegel #3204: Half Blue (1/2 CTB),
Cinegel #4415: 15 Green
You can buy the blues on Amazon.com and the green you have to get from Rosco.com. Keep in mind that some negatives have a strange color and you may have to play with the gels combo some but usually not. Main thing is to control the channels RGB to get them to line up better. Some negatives are more yellow and some are more magenta.
If you do not do this with the gels then your capture accuracy of the colors in the negative is poor and subsequent edits in Photoshop yields weird colors. This technique also keeps you from clipping the red channel. Ideally if you had a perfect camera with more than 14 bit capture you might be able to skip the gels but I found there really is no camera that can handle all that orange! Just make sure no matter what camera you use that you use the widest byte capture. Most DSLRs have a 14 bit RAW option. Also when converting your RAW image pre Photoshop and invert, use the Camera Neutral calibration.
Also you should expose less than you would normally think when capturing color negatives on a digital sensor. Remember that the shadows in the original scene are the clear (minus the orange cast) areas of the film so overexposing those makes your shadows in your final inverted image weird and the highlights look strange as well. The color gets crossed over and strange casts in highlights often and sometimes shadows. Middle tones are easy.
Lastly I should state that unless the camera you are using has excellent color rendering you will have issues. I have a D7000 and a D5000 and get poor results with both. Final image grain is high in the highlights (dark areas on the negative) and the colors are strange and never look right (crossed over) no matter what I do. I went with the D810 for better color and resolution and now get stellar results. It is much more linear in the shadows and highlights and thus works great for color negatives capturing and inverting.
See my physical setup on http://www.fechnerimaging.smugmug.com
Originally by user45778. Source · Licensed CC BY-SA 4.0
user45778
10y ago
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Yes—pre-correcting the light source is the key idea from the answers. Color negatives have a strong orange mask, which can push the red channel toward clipping when you copy them with a neutral light source. Instead of simply underexposing, try filtering the illumination so the RGB channels are closer together before capture.
One answer recommends adding gels to the light source, specifically blue/CTB plus a small green correction, to counter the mask and keep the red channel from being compressed. The exact mix may vary by film stock, since some negatives lean more yellow or more magenta.
If you have access to an enlarger with a color head, that can be an excellent DSLR-scanning setup. The color head can provide even illumination and adjustable filtration, letting you dial out much of the negative’s color cast before capture. The enlarger carrier also helps keep film flat.
So: expose to avoid clipping, but don’t rely on underexposure alone. Use filtration at the light source—either gels or an enlarger color head—to balance channels before shooting. That should make inversion and color correction much easier and more consistent.
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