Color films that are designed to produce positive images directly often feature the suffix “chrome” in their brand names, in contrast to the term “color,” which is typically used for negative film types. These chrome films are also known as color reversal films due to the specialized reversal processing they undergo. The results from roll films and sheet films are generally referred to as transparencies, while 35mm results are known as slides. Historically, these materials were predominantly used by professional photographers.
The amateur market for slide film has completely declined, and digital technology is rapidly replacing transparency film in the commercial sector as well. Slide and transparency films have traditionally been preferred for printed materials due to their high image resolution, unlike most prints which have to pass through a lens twice. However, in the present day, commercial magazines and newspapers primarily utilize digital files. Advances in digital imaging technology have facilitated the direct transfer of suitable image files via the internet, leading straight to print.
Reversal films possess a multi-layer structure incorporating blue-, green-, and red-sensitive emulsions, and most include yellow, magenta, and cyan dye-forming couplers, similar to those in color negative film. The results, however, exhibit stronger contrast and color saturation, and lack the ‘masking’ characteristic of color negatives, which means they do not have the overall pinkish tint. When viewed on a lightbox or projected as slides, reversal film images display a broader range of colors than is possible with paper prints.
In the initial stage of processing, only black and white developer is used, forming black silver negatives in the various layers. Subsequently, dyes form where the unused halides remain, so that when all silver is removed, a positive, correct-color image is produced.
All reversal color films require chromogenic processing using the E-6 development kit, similar to the C-41 process for negatives, which can be performed either by a photographer or in a laboratory.
Color balance must be more precisely matched to the type of lighting compared to negative materials, as corrections are more challenging. While digital corrections or printing adjustments are possible, projecting images from slide film complicates the process. Most color slide films are balanced for daylight and flash, but some are designed for 3200 K tungsten light. Daylight film requires a bluish filter when used with tungsten light, while tungsten-balanced film needs an orange filter for daylight or flash. Image color can be easily ‘burnt out’ by overexposure or darkened by underexposure, necessitating greater accuracy, as minimal correction is possible later, aside from some speed-rating compensation during processing.
Reversal films are available in a wide range of speeds and color contrasts, particularly in 35mm format, from ISO 25 to ISO 1600. Most films up to ISO 1000 are also available as roll films, while sheet films range from ISO 64 to 160. Tungsten-balanced films, typically ISO 64, have largely been discontinued. Most reversal films with ISO 200 or higher can be up-rated and push-processed to double their normal speed rating to correct exposure errors or facilitate shooting in dim lighting. Some films are specifically designed for up-rating, allowing up to four times the speed rating shown on the box, although increased image contrast and graininess are limiting factors.
Processed reversal film results are brighter and richer in hue than color negatives, requiring the brilliance of appearance expected in a final image, unlike an intermediate tailored for neg-pos-color printing paper. Different reversal films produce subtle variations in image colors due to the different dyes used by manufacturers.
Depending on the subject and desired mood, photographers can choose films with very saturated colors, warm saturation, optimized skin tones, or slightly warm balance for outdoor shooting in cloudy conditions. It is crucial not to mix reversal films from different manufacturers for a single assignment, as variations in hue and contrast will become conspicuously apparent.
