by
MichelB » Tue Apr 01, 2008 9:14 am
The real question is not IF you should shoot in colour then convert to B&W, but WHY you should do so...
Its' just because your camera does shoot 3 colors views in Red, Green, Blue at the same time. The raw data recorded is the addition of 3 distinct B&W shots taken with 3 different coloured filters (see this topic in the Newsletter #5). The built-in processor in your camera can keep this data for you to process later on, or it uses an average combination of the three shots to convert it to a usable RGB jpeg (or tiff) file.
If you shoot raw, the raw data is still there, even if you have chosen a B&W conversion mode on your camera. What you'll have recorded is a side note to the raw data indicating to the raw converter what your INTENT was. You can always change your mind afterwards. With more sophisticated cameras, you can even choose between several B&W conversion modes (portait, flowers, landscapes...) That's the same as the option PSE6 offers as B&W conversion, except that PSE6 let's you fine tune those preset choices.
Some have argued that a camera made specifically to shoot B&W would be much better for B&W. You can have a few highend cameras to be modified to do without the coloured filters and record only one view instead of three. In practice as well as theory, you get much more sensitivity as well as sharpness. Yes, but you lose the opportunity to work with the 3 channels. If you want to take advantage of coloured filters on your lens like you did in film days, you have to know it before... and you lose luminosity.
So, let's go back to all those who asked this question: they all have cameras shooting in 3 colours, even the simplest phone cell cameras... shooting in colour keeps all the recorded data for ulterior use. Either you can shoot raw or not.
If you can shoot raw, you have an enormous advantage. You can recover more than on stop of Dynamic range. It's even more important than when you want to shoot in colour, because in colour you could recover partly blown highlights, sacrificing colour accuracy. The other advantages of raw are still valid, especially working in 16 bits instead of 8 bits (much finer gradations).
If you don't shoot raw, you are not shooting with a DSLR or highend P&S, and your sensor has a very small area... then the quality of the recording in each R,G,B channel is less than perfect. Generally the green channel is OK (2 photosites, 1 for red, 1 for blue...), the blue channel is often very noisy and the red channel very flat... Examining the channels from a DSLR and those from a phone cell camera makes this very obvious.
On the other hand, the 3 channels may have specific qualities, not only defects when used to convert to B&W. Depending on your subject, you can use the blue channel to increase local contrast, the red one to soften skin, the green one to sharpen...
And don't forget that your software lets you use the channels to get the effect of coloured filters. You can even use them for different parts of an image. Think of a portrait with a skin with acne and light blue eyes... masking can give you the right luminosity and contrast in every part of the image, before converting, even if you don't work directly on channels, using hue/sat for instance. You don't need to be aware of the channels to do that, but you should not deprive your software of this important piece of information.
