Without a scanner - inverting repro-photos of black and white negatives with ColorPerfect / ColorNeg

Digital reproduction photography of black and white negatives can already present an attractive alternative to using a film scanner today. This especially holds true for users who do not own a film scanner but possess a high quality digital camera and a macro lens. The same applies for users in search of a faster digitizing workflow for their numerous black and white negatives. Since the technologies employed in scanners for the automated removal of dust and scratches generally cannot work for monochrome film both routes to digitize such film will require about the same amount of retouching.

Depending on preexisting gear and your budget there are numerous ways to approach digital reproduction photography of negatives. In general it should be ascertained that the optical axis is in the center of the negative, that it is parallel to the digital camera's sensor plane and that it is flat. An even illumination, set up in a way that allows the light to travel through the negative in direction of the camera or so that a uniform surface behind the negative gets illuminated in a uniform way, is also required.

 

Apart from the digital camera and lens the most simple setup only requires a tripod, something to hold the film flat and a light source. Commercial repro-photography solutions in the form of slide copying adaptors are available on the market from several manufacturers. These are also referred to as slide duplicators. If available a slide projector without its own lens or the head and film carrier of a photographic enlarger can also be used. The latter option is shown in our example of a reproduction setup above.

Workflow for creating linear Tiff files from digital repro-photos of black and white negatives using MakeTiff

All reproduction photos should naturally be taken in RAW mode. Our auxiliary program MakeTiff makes creating linear Tiff files from such photos very easy. Tiff files in general can be opened with Photoshop, Photoshop Elements and PhotoLine without any mandatory processing being applied to the image. Therefore linear Tiff input is required for inverting repro-photos of negatives in ColorPerfect's ColorNeg mode.

After starting MakeTiff all it takes to create such is dragging and dropping the desired RAWs onto the program's interface. The Tiff files are then created in the same directory as the photos.

The Tiff files are always created in RGB mode. If you'd like to use grayscale mode for the negative conversion process you should first assign an RGB profile to the image (Photoshop > Edit > Assign Profile) that uses the same gamma or tone reproduction curve as your desired grayscale working profile does. Possible combinations in this are: Apple RGB and Gray Gamma 1.8, Adobe RGB 1998 and Gray Gamma 2.2, sRGB and sGray. Alternatively you can also configure the desired RGB profile in MakeTiff. In that case it will automatically get assigned when creating the Tiff files.

In addition to assigning the matching RGB profile you need to use Photoshop > Image > Adjustments > Channel Mixer with its Monochrome checkbox ticked. That check box is located at the bottom of the dialog. This removes any color cast from the repro-photo. As long as they add up to 100% you are free to vary the values of the Source Channels in this process.

After this step explicitly convert to the grayscale working profile of your choice (Photoshop > Edit > Convert to Profile). The channel mixer step is required because the conversion process would impair the tonal values of the negative if the source image were colored.

As an alternative to the method above you can also exclusively use the green channel of your reproduction photo of a black and white negative. The green channel differs from the other two color channels insofar as there are twice as many pixels on the sensor that capture green light. In Photoshop choose the channels panel and select the green channel by clicking on it, select all pixels (Ctrl+A), copy them (Ctrl+C), create a new Document (Ctrl+N, Enter), paste the grayscale image into the new document (Ctrl+V), flatten it to its background layer (Ctrl+E) and then assign the grayscale working profile of your choice to it. You can read more on using ColorPerfect on monochrome images in our article on that topic.

After invoking the ColorPerfect plug-in on your image choose ColorNeg mode and set the Gamma C setting on the Start panel according to the grayscale working profile or RGB working space of your choice. To obtain consistent and reliable results always use MakeTiff and do not open the repro-photos directly. Only MakeTiff offers access to the already interpolated but otherwise unchanged sensor data which is the closest you can get to an actual linear negative scan.

Establishing the ideal exposure settings for photographing the black and white negatives

 

Because repro-photography usually allows for working with constant illumination levels it is best to take the photos using a fixed set of settings in a fully manual camera mode. In this the camera's ISO or "film speed" setting should be set to its lowest value which will minimize digital noise. Furthermore the aperture should be set to an f-stop like 8 or 11 that is suitable for the task. That leaves the camera's exposure time as the last variable in exposing the photo. It should be varied in order to find the optimal setting.

If the exposure time cannot be varied, e. g. when using a flash, intensify or lower the light level or move the light source closer to or farther away from the subject. Only after these options are depleted open the aperture further.

During searching for the ideal camera settings the camera's own histogram output can be used as a loose guideline. As soon as one thinks to be content with that a first shot should be converted into a linear Tiff file using MakeTiff and the result should be evaluated in Photoshop by looking at the histogram display there. The linear Tiff file of such a first shot could look like the one shown to the right. Because cameras will always show the histogram of a JPEG made by their intrinsic image processor that form may have very little in common with the actual sensor data's histogram we see now.

The linear Tiff file made by MakeTiff is going to look pretty dark prior to inverting the negative. That is normal and expected because when working with ColorPerfect you will have to assign an RGB color space or grayscale working profile that matches the final positive image result produced by ColorPerfect's ColorNeg mode. The perceived darkness does not go along with a lack of detail but rather is only about display settings. If we were to flag the linear data as such temporarily to better view the image on the screen it would look much brighter than its dark rendition shown before. Note that the image data itself stayed completely unchanged while doing that.

The histogram of the initial linear Tiff file is obviously not fully populated. For better orientation we have put two scales above the histogram. The upper scale shows full f-stops and the one below 1/3 f-stops. At first we are only interested in the brightest of the three color channels. If the data on that channel ends before the middle of the histogram we can add one exposure value (EV) of light. If less than one fourth of the histogram bins were populated we could add two EV. If we add 1.3 EV in our example image by lengthening the exposure time accordingly the maximal amount of detail the camera is capable of capturing will be captured.

To ease the finding of a universally applicable set of settings the test photo should include some unexposed film base because nothing on the negative film can ever be brighter than that. The repro-photos of negatives may never be overexposed. If they were you'd be able to tell by a tiny to significant spike at the rightmost histogram bin.

The differences that exist between the three color channels depend on the nature of the light source and the properties of the digital camera's sensor. Of course color compensation filters can be used to even those out but that has very little to no practical advantage for black and white negatives. Because it was so straightforward to do with our demo set up of using a color photographic enlarger as the film holder and light source we did use that anyway to produce the base image for our following quality comparison. Please note once more that it is preferable to leave some histogram bins unpopulated so that we do not risk overexposing our repro-photos.

Comparing the quality of a repro-photo made with a digital camera to the quality of a film scanner

 

In the following we are going to compare the results of film scanner and digital camera by creating two according inversions of the same black and white negative using ColorPerfect's ColorNeg mode. Our starting point for the digital camera sample image is the final state we arrived at with the exemplary set up above. That is a linear digital repro-photo that was shot using a color enlarger's head and a macro lens (Nikon AF-S Micro-Nikkor 105mm 1:2,8G VR on a Nikon D300s shooting in its 14 bit RAW mode).

To compare we will be using the linear scan of a dedicated film scanner (Nikon Coolscan LS 8000). After inverting these two captures of the same negative using ColorNeg mode the difference between the version made with the film scanner and the version made with the digital camera is remarkably small - at the very least when looking at a small to medium output image size. The two captures of the negative were processed using similar but not identical parameters in ColorPerfect's ColorNeg mode. In fact only the settings Black and White were varied a little to obtain two images that are as similar as we could make them visually.

When viewing the tonal values of the linear scan and those of the repro-photo which was converted to a grayscale form according to our instructions above we note that the tonal values start somewhat farther to the right in case of the repro-photo. That can be explained with several influencing factors being the diffuse light source, flare and intrinsic camera noise opposed to the film scan which was made using multisampling and thus entailed reading each position that became a pixel in the final image four times. In theory it should be possible to compensate for this difference prior to inverting the negative. In practice it is close to impossible not to ruin more than one could ever gain from such an attempt. Such differences can relatively easily be compensated using ColorPerfect's various tools after the inversion of monochrome images so we recommend against any kind of image adjustment prior to inverting negatives.

When comparing the quality of both versions in detail we will find that the film scanner is delivering the sharper result that shows a little more detail, too. The scan shown was resampled to about 70% of its original resolution of 4,000 dpi so that we were able to precisely overlay it on the repro-photo shown at 100% magnification. It should be noted that the example image was shot handheld with a manual camera under mediocre lighting conditions with the aperture wide open and using Kodak's T-Max TMY 400 film so that it always seems to be slightly out of focus when viewed at these high magnifications. The scan has not been digitally sharpened while the repro-photo has been to compensate for the anti aliasing filter placed above the vast majority of digital camera sensors. That filter inevitably leads to a somewhat softened capture as can be evaluated in this original version of the repro-photo that did not receive any sharpening. The diffuse light source of the color enlarger used is very likely to have intensified that softness a little further.

To create the digital positives images shown here we used the ColorPerfect controls Black and White, ColorPerfect's highlight and shadow compression, its zonal system and a FilmType from our list of virtual grades.

Doesn't this workflow also work for digitally reproduced color negatives?

A physically correct negative inversion is probably the most extreme image adjustment there is. The method described above for reproducing black and white negatives regrettably does not lead to results that equal those of a film scanner for color negatives. In developing ColorPerfect's unique PerfectRAW system we have analyzed and understood the physical basis of this. We hope that the results of that research will allow us to introduce the functionality to process color negatives captured with digital cameras in high quality in a future version of ColorPerfect. If and when that will happen is not yet foreseeable.

We are aware of the fact that some of our users do digitize color negatives using digital cameras in varying ways and report that they are obtaining results they are content with. We are pleased that they are happy with ColorPerfect in that regard. Physically all such methods that have been described to us over the years are really far out so that we will neither detail nor recommend them here. The standard for what we feel we can recommend in regard to color quality and color integrity is set high. Without those aspirations there would probably neither be a ColorPerfect nor a PerfectRAW today.

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