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February 01, 2006
[ BLACK AND WHITE ENVY ]
“Why doesn’t my Nikon D70s digital single lens reflex take black and white pictures?” an inquirer asks. After all, just about every digital camera on the market, from the cheapest up, has a monochrome mode selectable in the menu. Why does the superior Nikon not have it? And why does the more expensive, new Nikon D200 come with black and white mode?
The answer to the plaintive question is probably that Nikon thought a monochrome mode unnecessary when the D70s was designed but for some reason -- perhaps customer complaint -- they have included it in the D200.
There is a serious argument amongst digital photographers over the best way to render images in shades of grey. The weight of opinion from the aficionados favours post-camera conversion of the coloured original. In fact there is some haughty contempt for the in-camera black and white image because it is, in fact, an RGB image that has been desaturated in all channels, so you might as well do it yourself.
dpexpert has been playing around with images from the Nikon D200, comparing the in-camera greyscale images with converted colour in Photoshop.
Our preferred conversion method consists of opening the colour image, converting the Image/Mode to Labcolor, selecting the Lightness channel and then changing the mode of the Lightness channel to greyscale. Then create a Duplicate Layer, change the Blend mode to Multiply in the Layers palette and adjust the Opacity slide until the image looks about right.
At that point flatten the layer and tweak the Curves.
A simpler method is to open the Channels and examine the red, green and blue channels individually and choose the channel that seems to have the best tone rendering and convert that to greyscale and tweak with curves. This method can produce good results.
Simpler still is to open Image/Hue & Saturation and desaturate the image completely. This is more or less what the in-camera system does.
The monochrome image straight from the Nikon D200 is a fairly flat, low contrast picture, which is not a bad thing. It has the qualities of a well-exposed and developed negative. Just as a negative with a wide tonal range from black to white is ideal for printing so a similar digital file gives a lot of scope for manipulation in the digital darkroom.
In the end we could not tell much, if any, difference between the in-camera and the converted colour method of getting a monochrome image. The final judgements about black point and white point in the picture and the breadth of the tonal range are subjective anyway and the same end results can be achieved using either approach. The most important thing is to make sure that the original image has detail in both highlights and shadows. If they are not there in the original they cannot be put back later. With film and paper the general rule of thumb was to expose for the darkest area in which you wanted detail preserved (in other words, over-expose) and then develop for the highlights (under-develop). With digital the best approach is to expose for the highlights (underexpose) because digital sensors seem to be better able to preserve shadow detail than highlight detail. And blown highlights are uglier than inky shadows.
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Posted by terry at February 1, 2006 08:00 PM