Converting Color Film Negative to Positive Using Photoshop by Removing the Orange Cast
|by Jeffrey Sward
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|Orange Cast in Color Negatives
All color film negatives contain an orange cast throughout the negative. The orange cast is clearly visible in unexposed areas, such as the around the edges or around the sprocket holes. The reason an orange cast was added to color film negatives is because of imperfections in the cmy dyes. A technical discussion of the orange cast can be found in this article about color negative orange cast. Because the entire film stock contains the orange cast, the lightest part of a color film negative (and hence the darkest part of the scene) can be no lighter than the color of the base orange cast. This equating of the base orange to the lightest negative part is important theory when removing the cast using the Type IIa method below.
|Converting Digital Scan of Color Negative Into Digital Positive
Photoshop contains a simple command for converting negatives to positives and vice versa, namely image => adjustments => invert. Invert works perfectly with black and white negatives. However, when starting with a digital original of a color film negative, the orange cast in the color negative will be converted into a purple cast in the positive if invert is used by itself. Therefore the simplest way to convert color film negative scan to positive is to first remove the orange cast. After the orange cast is removed, then image => adjustments => invert works correctly.
|Type I: Original Made by Film Scanner
If the digital image of a color film negative is made with a film scanner, then most of this article is irrelevant. All film scanning software comes with color negative options. Look for color negative options in the scan software. Typically a variety of color negative film types are presented in the film scanner software, such as Kodak Gold 100, Fuji NPS, etc. Ideally, match the film type of your color negative to the list of films in the scanner software. If you do not know the type of film of the color negative, check the edges of the negative. Often the manufacturer shows the film type on the edge. Do not panic if your film is not listed in the film scanner menu or you cannot determine the negative type. If the match is unknown, experiment and select the combination which works the best.
After scanning a color negative with a film scanner using the color negative software setting, the resulting file will be a normal positive image. If the output of the film scanner is not a positive image, check the software settings and try again.
When doing any film scanning, either of negatives or positives (slides), the objective of the scan is to avoid clipping in all of the color channels, not making the scan look good. Clipping can be checked by examining the histogram of the scan. Most scanning software allows a preview of the histogram before the final scan. Otherwise, the histogram should be checked in photoshop. A good histogram will show a "bell shaped curve" in each of the color channels, with none of the histogram bumping either the left or right edge. Bumping the left or right edge indicates clipping, which is equivalent to a resulting value of either 0 or 255. If the histogram shows clipping, then repeat the scan after adjusting exposure, contrast, etc.
Once a film scan is made which contains full and complete data is each channel, then a regular workflow is applied to the image in order to correct and optimize the tones. Refer to this author's discussion of photoshop workflow.
|Type II: Original Made by Digital Camera (or Scanner Could Not Convert Negative)
Another method for making a digital file of a color film original is with a digital SLR camera, macro lens, film stage, and light source. There are various commercial gadgets which will facilitate photographing a slides or negatives with an SLR camera. An example of a film-to-digital-SLR-camera gadget can be found at Specialty Photographic. Or, it is possible to construct your own setup with a copy stand, macro lens, enlarger film carriers as the stage, an electronic flash, a diffuser, and a box to hold everything. Since the result here is a picture of the color negative, the orange cast will remain and must be removed at conversion to positive time.
|Correcting Type II, Method A: Conversion by Photoshop Only
As noted above in the background discussion, the lightest part of the negative (and hence the darkest part of the scene) can be no lighter than the color of the base orange cast. Therefore, if the orange cast can be converted to pure white in the negative file (black in positive), then the remainder of the colors by definition will be converted correctly since nothing can be lighter than the base orange.
Note: per this author's discussion of Photoshop workflow, the "save as" method is recommended in general and is reflected in the steps below.
The following process works well. Note: every type of color negative film has a slightly different orange cast, and the orange cast will vary from scan to scan. Therefore, the following steps need to be taken individually for each image.
|Type II Method A Conversion Example
|Correcting Type II, Method B: Conversion by Photoshop Plug-In or Commercial Software
At least two software products will convert the color film negative digital file with orange cast to positive. Neither of these has been tested by the author, so inclusion here is information, not an endorsement.
A Photoshop color negative plug-in (ColorNeg) is available at c-f systems.
VueScan is stand alone software which runs scanners and will reportedly also "scan" a digital original in tiff or jpeg format. VueScan is available from Hamrick
A canned photoshop action is avaialbel at https://photoshopcolornegatives.weebly.com/.
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