Back in the day when I worked in a full service photo lab color negative (C-41) was our bread and butter. We offered traditional prints and scans along with the film developing. Even in the mid 2000's using the latest digital/hybrid minilab systems, most labs often relied upon the automated software to do the color and density adjustments. I worked with both Noritsu and Fuji Frontier labs and they both do an excellent job scanning color negative film.
Every film stock is different. That's the whole point of shooting film, right? Choosing the film that will reflect the vision you have for the subject. There are differences in overall color balance, saturation and contrast. To really dial in the best scans, I was able to create different channels for each film stock. Along with the frame # barcode along the lower edge of the sprockets, included a code. This encoded number for each film stock was different, similar to the DX code used to automatically set the ISO on your camera. The Noritsu allowed me to set up a custom channel for each code. I could name it, of course, but the power lied in the ability to create a saved set of color, contrast, density, sharpness and saturation level for each film stock.
I wasn't too concerned with tweaking contrast and saturation. Those are already baked into the emulsion through the individual stock characteristics at the time of manufacturing. This goes back to my earlier point about shooting a specific film for its look. Think Kodak Ektar 100, for high contrast and saturation, as this is created for these specific outputs. My focus was on getting the most accurate color balance so each roll did not have to be adjusted to correct imbalances - with the exception of lighting or color failure from large areas of solid color where the software really isn't able to fitness the right color.
So how did I achieve this? With the use of a set of printer control negatives. Up until the late 2000's a company called Aperion, Inc. (no longer in business) created a set of control negatives for every film stock of the day. This included a series of color patches and greyscale patches from DMIN to DMAX. In addition to the patches a head shot of a mannequin was included to reference skin tone. I used a set of these negatives to adjust the color balance of each film stock, using the color and grey patches as reference. The on board software is creating it's own balance by removing the orange mask and converting the image to a positive. Each stock has a slightly different orange/red mask and needed adjusting to get the best color balance.
I eyeballed the color of the grey patch to determine if it was neutral. If not, I would add or subtract the required color to adjust the final image to the most neutral color balance and they lock in the those C M Y values in the master channel for each stock. If you really wanted to be accurate, you could read the grey patches on a lab densitometer and read the values for each R G B channel, think 80-80-80 for example would be neutral and the "perfect color" although it was never perfect by the nmbers, I could get it pretty close. This is exactly the same method you can use to adjust color balance in photoshop and use levels or curves - grab the grey dropper to click on a known grey or neutral value in the image (black and white tones as well) and get a fairly neutral color balance.
Digital minilabs such as the Frontier and Noritsu's are able to create a much more neutral balance between normally exposed negatives and those that are under and overexposed. Traditional minilabs that did not use digital scanning, relied on a lamp projecting through the color negative image onto color paper inside the machine. That paper was then sent into the RA-4 color paper chemicals via belt and then processed through the developer, blix and stabilizer than finally washed and dried and out the sorter in about 5 minutes. Color paper was designed to handle the exposure + color balance while offsetting the orange mask to create the final color print. However, under or overexposed negatives of +/- one stop or greater posed a challenge. If you've ever printed in a conventional color darkroom using an enlarger, you quickly learn that density effects color balance. The more or less exposure you give the color paper to correct for the under or overexposed negative, the color balance will shift. The same was true for photo labs that used traditional printing from color negatives. To offset this, the aforementioned Aperion company created an identical image as the standard "normal" exposure and provided an under exposed and overexposed on the same negative strip. Before digital scanning, the operator created similar channels for each film type and this also included an under and over setting separate from the normal. This was called the slope setting, as the characteristic curve of the paper differed with shorter or longer exposure times reflective of the density of the negative being printed. While a "normal" exposure looked balanced, the "under" frame, when printed would shift color, due to the slight difference the paper received to light exposure. It often had slight magenta shift. By using the under exposed balance negative, you could subtract magenta and save it within the under slope or the under setting. This would correct all future prints that were underexposed when the customer used that particular film type. The same adjustment can be applied to the overexposed channel as well. This provided a clean, color balanced set of prints for the customer even if the entire roll was not perfectly exposed.
As Aperion, Inc is no longer, there is no other way to get a control negative without creating your own. I haven't been able to locate any, even on ebay. The film stock options available 20 years ago are no longer manufactured. It would be nice to have some of those old packs to use today for creating custom channels when scanning those stocks today. Which I have done! I used a color checker and Kodak color patch and exposed each film stock against a neutral grey background in daylight conditions. I exposed the set 3 ways, normal, under and over. I can take this control negative, scan it on my Epson V850, Plustek 8300i or use my DSLR scanning setup to create a custom channel either in Silverfast or in Negative Lab Pro. Referencing the neutral color patches with the white balance tools each the software will create a custom white balance from each film stock. Those values can be saved and then opened in the future when converting the files to positive images. As soon as I get the film developed, I will update the blog and create a how to video! The setup negative scan image shown above was created using Kodak Gold 100, as it was presumed back in the day that you would set up your printer using Kodak Gold 100 as your "master" color balance. Some labs preferred to use Kodak Gold 200 as that was more commonly used film stock.
Chris
