Exposure and tone curves

There are two different ways of creating image files with the D70 (or any other DSLR). Either you shoot in JPEG or you shoot in RAW/NEF. (Yes, you can set the camera up to produce both kinds of files at the same time.) A good camera should support both ways equally since they are for different purposes and occasions. If you shoot in JPEG, the camera does the image processing, converting pixel read-outs from the sensor to an image file. This involves operations like interpolation, demosaicing, white balancing, image correction, and more.

For one thing, you want the image to be exposed correctly. Nikon cameras, especially the early ones, have been accused of underexposing. This is of course not an error but a design choice. Among the serious amateur cameras, it was especially evident on the Nikon D100 which tends to underexpose down to −1/2 stop. The D70 rather tends to underexpose about −1/3 stop on average. This is inconvenient for JPEG shooters since the images often wind up darker than expected and you have to constantly apply exposure compensation to deal with it. This also leads to not paying attention to the compensation symbol +/− which would otherwise warn you about non-standard settings. For JPEG, this is a poor design choice (not a manufacturing error or malfunction). On the other hand, if you shoot RAW/NEF, the meter’s behavior is made for you. Underexposing preserves highlights which can be recovered in post-processing. You can bring the skies, for example, up in post-processing and recover details that would have been lost in a standard exposure. In 2000, Nikon were newbies in digital and worried too much about lost highlights. They designed the D100 with too big a margin. They shrunk the margin with the D70 but it is still there. I would say they got it right for RAW on the D70 but not for JPEG. The real mistake made was not making the exposure behavior configurable with each image file format. There are times when you want to shoot one format or the other. It’s not that one format is “better” than the other. They are different and made for different purposes. I would like more standard exposure when shooting JPEG but keeping the underexposure behavior for RAW/NEF.

So what did people do? Some clever people tried to use a function in the D70 called a custom tone curve to obtain an overexposuring offset to the inherent underexposure. In essence, a custom tone curve is a new contrast curve that replaces the in-camera contrast curves. At first, the idea might seem good. Back in 2004-2005, there was a number of curves being created by those people and discussed on several web forums. After some initial fuzz, they fell into oblivion because they didn’t work as intended. A longer discussion on tone curves (primarily for the D100) is found here.

There are two uses for a tone curve, the first being to offset exposure tendencies and possibly try to change the dynamic range as you go along. This is unfortunately bound to fail; the D70 does a better job than you can in automatically selecting contrast according to the image and the exposure. Thus, the only way to handle the JPEG underexposure tendencies of the D70 (and others) is the good old exposure compensation button and dial. Even toy cameras like the D3100 have that accessible through a button on the top close to the shutter release button.

The other use is much more interesting when you want to shoot JPEG and have reasonably ready images out of the camera that requires a minimum of post-processing. The D70 (and some other Nikons) have been accused of having a “dull” rendering. I would rather call it accurate, but it is not always that you want a very accurate rendering. Sometimes, you rather want a more colorful, vivid “slide film like” rendering, although not as extreme as for example Fuji Velvia which I personally find too bold and punchy. There are a lot of options possible on the D70 when it comes to image rendering. These options are called Image Optimization by Nikon and are found in the menu system. While the settings available are not bad, they are a bit conservative. The Vivid option, for example, is not very vivid. This led people to develop tone curves for this second purpose, and they can again be found on the web. Here is an example of a repository for curves for both purposes. Many of the curves available at that time mixed the two purposes up – adjusting exposure and changing the tone. Others went, in my opinion, either too far (for example trying to mimic Velvia) or missed the target. Another misconception at the time was that it should be possible to find a curve that fitted all shooting situations. There will never be such a curve.

All this led me to develop a curve with the single purpose of changing the tone balance, not compensating the exposure system of the D70. The neutral rendering of the D70, being an asset in some images, needs to be supplemented in some situations with a curve that feels more like slide film without going to Velvia extremes. The curve has been developed over many years and is, to my knowledge, the only curve still being maintained today. The curve has been derived from thousands of images of all kinds. In my view, it works well with everything from nature to street, from buildings to ants, from cars to ships, but not for people, products, or paintings that require either duller or as neutral rendering as possible. For the latter ones, it is easy to select other image options on the D70 and still keep the custom tone curve for later. The curve is called D70 Chrome and is available for download.

If you have a D70, try it and enjoy. The download to the camera requires Nikon software (Camera Control Pro) and the USB cable that came with the camera. You need not buy Camera Control Pro, the trial version is enough. You are given a 30-day trial period of which you need a couple of minutes. Once downloaded to the camera, the tone curve stays there and you need only to activate it when you want to use it just like any other, built-in tone curve.This is the way to download it from a PC:

1. Download Camera Control Pro 2 from a Nikon website to your PC. Any version from 2.5 up to 2.11 will do. From 2.12, the D70 (along with the D2-series, D200, D100, D80, D50, and D40) are no longer supported. Note that you cannot have multiple versions installed, such as 2.11 for your D70 and 2.12 for your D600 (which is only supported from 2.12 onwards). A catch-22 if you have an older camera (such as the D70 or D200) and a newer (such as the D600 or upcoming models).

2. Install Camera Control Pro and accept the trial period. If you have Windows 7, make sure the application runs in Vista SP2 mode, or you might get problems with connecting to the camera. Drivers are not fully compatible with Windows 7.

3. Restart the PC to have all drivers installed properly.

4. Download the D70 Chrome custom tone curve and save it in a directory on your PC.

5. Before connecting the D70 to the PC, make sure you use the PTP protocol. You select PTP mode under USB in the tools menu on the D70. This is a two-way protocol that allows the PC to actively talk to the camera, not only receive files as you can do also in Mass Storage mode.

6. Follow these instructions. Never mind the Japanese, your dialogue windows will look the same except for the text.

7. Enable the custom tone curve in Shooting menu > Optimize Image > Custom > Tone comp. > Custom. After this selection, you MUST select Done or your setting will not have any effect! Enjoy your shooting.


2 thoughts on “Exposure and tone curves

  1. The link given for the “D70 Chrome” curve leads to the “Just Cloud.com” website where I am invited to subscribe. No sign of a tone curve. What’s the deal here?

    • Hi! It turns out that the cloud operator that hosted the file has lost it along with all backups. For the moment, it’s all lost and gone. Hopefully, there is a copy somewhere out there that I will get hold of so that I can restore the link.

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