Creating a Custom Color Negative Film Setup for Imacon Scanners
By Michael E. Fox Last Rev: 25-Mar-2003
Note: Screen shots would be helpful. I'll add them when I have some time. However, the text should be self explanatory to any Imacon Flexcolor user.
Scanning color negatives can be difficult since the scanner operator does not have a positive original for comparison purposes. If the scanner is not set up properly for the type of negative film being used, the resulting scan will contain color shifts due to incorrect neutralization of the amber mask of the negative and due to the differences in the color palette of the film. Without a positive original for comparison purposes, the scanner operator may have quite a bit of difficulty correcting these color shifts since the operator won't know what the positive image is supposed to look like.
In the past, it took years of training to learn to scan color negatives well. But today, software such as Imacon'sFlexColor includes setup files for many types of negative film. These setup files adjust the scanner for the particular characteristics of each film type and allow repeatable results.
Unfortunately, film emulsions vary and film processing varies. So the individual photographer may find, as I did, that the setup files supplied with the Imacon scanner do not provide satisfactory results. That's o.k., because Imacon also provides the tools to create custom setup files. With the excellent tools available in the Flexcolor software, the operator can quickly create a custom color negative film setup file that will produce excellent scans over and over again.
As with any type of profiling or setup in a color managed workflow, it is best to update this setup file whenever there is a significant change in the workflow. I would certainly recommend making a new setup file if you change processing labs. Determining whether other changes (emulsion batches, etc.) are significant or not is an exercise left to the individual photographer.
The purpose of creating a custom negative setup is to create a known, repeatable environment that produces a positive image that is as close as possible to what is captured on the film in negative form. From that point, other controls can be used, either in the scanner software or in image manipulation software like Photoshop, to make enhancements to tonality, saturation and other image characteristics.
In creating the customer color negative film setup file, there are two principle goals to be achieved:
- neutralize the amber mask of the color negative film
- set the black and white points to the full range of possible values so that no clipping of shadows or highlights occurs.
In neutralizing the mask, it is important that we neutralize the shadows, the highlights AND the midtones. Only by neutralizing all three areas can we achieve a close match to the true colors represented by the negative. Of course, neutralizing the shadows and highlights is dependent on where the black and white points are set, respectively.
Setting the black and white points is important from an overall contrast perspective. Since we are creating a set-up file for a particular film type, the goal of this procedure is to set the black and white points as close as possible to the maximum dynamic range of the film -- NOT the maximum dynamic range of any one image.
Setting the black and white points to the maximum range of the film insures that no future scan is clipped in either the shadow or highlight area. This insures that the full range of highlight and shadow values will always be contained in the scan. The result, of course, is that many images will appear rather low in contrast. But more contrast can be easily applied either in the scanner software or the image manipulation software (such as Photoshop). Going the other way (reducing the contrast), can be difficult, especially if a given image does not have perfectly white white and a perfectly black black.
So, to summarize, this procedure will set the black and white points to the worst case black and white values possible. The image will then be neutralized at the black point, the white point, and a midtone.
- Locate or create two images.
- Both images should be on the negative film for which the setup file is being created.
- Both images should be carefully created in the proper light. For daylight film, be sure to shoot the image in light balanced for daylight film and/or use proper filtration. The more exact your light balance in the original negatives, the better the setup file that you will create.
- Both images should have been processed using whatever the normal processing procedures are.
- One image should be a normally exposed image that contains a neutral gray patch. A good example is to shoot a properly exposed image of a Gretag Macbeth Color Checker chart. In fact, the best choice is the Gretag Macbeth Color Checker DC chart since it contains many different neutral gray patches.
- The second image should be a dramatically over exposed image that contains a neutral white patch. A good example is a second shot of the Gretag Macbeth Color Checker chart but overexpose by a lot say, 7 stops.
- It is easiest to use either 35mm or medium format film since this makes it easier to place both images in the film holder. However, if concerned about emulsion batches, any size film can be used.
- Place both images into the film holder
- Use a film holder that will allow both images to be placed in the holder together. Regardless of the film type used, this is easiest with the 6cm x 6cm x 2 medium format holder or the 35mm strip holder.
- Insure that the overexposed white patch is visible.
- Insure that the normally exposed gray patch(s) is(are) visible
- Insure that some of the unexposed border (the area between shots on roll film or surrounding the image on sheet film) is visible
- Select a random color negative film setup file from the Setup menu
- It doesn't matter which one you select since it will be changed and then re-saved as a custom setup
- Perform a Preview
- Press the Preview button
- The image will probably look terrible. That's o.k.
- Reset any settings that may be in place
- Press the Reset button located in the Correction area (next to the Auto button)
- The image may now look even worse. That's o.k.
- Open the Histogram Tool
- Window >> Histogram
- Set the Black Point
- Click on the Black Eyedropper (far left) in the Histogram tool
- Move the eyedropper over the unexposed border area of the film. Find the darkest part that you can find (values as close to (0,0,0) as possible) and click there.
- This does two things:
- It sets the low end of the tonal range to the lowest possible value for this combination of film and developing. This value is typically called Film Base + Fog. No shadow value in an image will ever be darker than this black (lighter than this on the negative) so you know you that future scans won't clip any shadows.
- It sets the RGB values to (0,0,0) so that the low end of the tonal range is neutral
- Set the White Point
- Click on the White Eyedropper (third from the left) in the Histogram tool
- Move the eyedropper over the overexposed white patch. Find the lightest part that you can find (values as close to (255,255,255) as possible) and click there.
- This does two things.
- It sets the high end of the tonal range to the highest possible value for this combination of film and developing. This is typically the maximum density (Dmax) that this negative film will support. No highlight value in an image will ever be lighter than this white (darker than this on the negative) so you know that futures scans won't clip any highlights.
- It sets the RGB values to (255,255,255) so that the high end of the tonal range is neutral
- Neutralize the midtones
- Click on the Gray Eyedropper (middle one) in the Histogram tool
- Move the eyedropper over the neutral gray patch in the normally exposed image and click.
- If you have multiple shades of neutral gray shades in the image (like from a Gretag Macbeth Color Checker DC card), try clicking on different shades of gray.
- While looking at the actual Color Checker card (or whatever target you used in your images), compare the results on your screen with the actual colors in the card. Check the light, pastel colors and the dark colors. Check the saturated CMYK and RGB patches. Click on different gray patches until the best match to the original image is found.
- Configure Color Management settings
- Go to the Setup menu and select the ICM (PC) or Colorsync (Mac) tab. Set it to match your current profile settings.
- Create the new custom setup
- While in the Setup menu, click on the General tab.
- Click the New button
- Type in a name for your customer setup, then click O.K.
- Then click O.K. on the main Setup window
The procedure outlined above is designed to create a setup file for the worst case dynamic range that might occur on a particular film type. The benefit of doing this is that neither shadows or highlights will be clipped in any future scans. The downside is that the dynamic range may be too wide for some low contrast images.
One possible enhancement to the procedure is to create multiple setup files. One could be created according to the procedure above and used for maximum contrast images. Another setup file could be created using a lower value for the white point and possibly a higher value for the black point. This would result in a properly neutralized scan which has a more narrow dynamic range (higher contrast). This second setup file could be used on low contrast images. However, care should be taken not to allow clipping of either the highlights or the shadows. Simply check the histogram. If clipping is present, use the setup file with the wider dynamic range.
Application to other film types
A similar procedure can be applied to transparency film. Doing so would obviously make it easier to neutralize the color palette of a given transparency film. Of course, this may or may not be desirable. Only the individual photographer can decide.
Application to other scanners
Some film scanners provide an automated method for neutralizing the amber mask of color negative film. The procedure usually involves selecting or clicking on an unexposed but developed piece of film (or unexposed border), followed by the scanner software automatically creating a set-up file.
I have found this to produce only marginal results since this only neutralizes the shadows and not the midtones or highlights. It also doesn't set the dynamic range.
For these types of scanners, a custom setup file as described above is not possible. However, a similar procedure can be used on each scan. Simply include the two test images used above in the Preview of the actual film to be scanned. In other words, when scanning a piece of negative film, put the negative plus the two test negatives into the scanner at the same time. During the preview, use the two test images to set the black point, white point and neutral midtone. Then adjust the selection to include just the desired negative prior to performing the real scan.