Digital BW, The Print

What filtration does is to attenuate specific wavelengths of light. For 
example the yellow filters will attenuate blue light the "12" will 
attenuate more blue light than the "8".  This has the effect of changing 
the relations of the light power of the colors in the scene on the 
sensor. For example B&W film - and the same would apply for monochrome 
CCD sensors - various levels of yellow filtering can be used to darken 
the areas of primarly blue light ( the sky and areas lit primarly with 
skylight, i.e. the shadows vs. the other aeas ).

What I take away from the thread this type of filtering during image 
capture could be an advantage since it might compress the dynamic range 
in the image. The effect of this filtering can then be inverted in 
follow on processing. This inversion would probably work pretty well for 
B&W - I did some playing aroun with it about 3 years ago. On the other 
hand the inversion would probably be very problematic if a color image 
was your desire.

One the other hand I am not sure it will buy you much most of the time. 
For example in the example above, in general the sky is not the brightes 
area in a scene - hence the exposure won't be dictated by the sky. The 
yellow filter will, however, lower the values of the shadows lit by 
skylight (primarly blue) which may actually increase the dynamic range 
requirement if the shadows are important to the shot. Also the use of a 
yellow filter will reduce (one the average) by 1/2 the light power 
hitting the sensor and hence would require a slower shutter speed and/or 
lower f-stop.

In my experimentation a few years ago, I didn't see that it made much 
difference. However, I must admit that I was more interesting in 
determining how the use of the traditional B&W filters could be used to 
change the color make up of the captured image and how that related to 
filtering after the fact and how that related to the final B&W image. I 
didn't do in dynamic range test.

With film we have many options to expand or compress the dynamic range 
of the film through development. The dynamic range of film can be 
expanded quite a bit by using different developers, different dilutions, 
two part development, different agitation, etc. In digital the dynamic 
range we get is that offered by the sensor and the electronics in the 
circuit. You get what the designers give you.  I would expect that in 
the next 5 years we will see improvments in dynamic range of the 
sensors. It seems till now the camera have been playing the "megapixel" 
game rather than increasing the dynamic range of the pixels. Today the 
improvments in more pixels - at least in the DSLR - seemed to have 
reached the level of dimishing marginal returns. Now maybe someone will 
concentrate on the sensitivity and dynamic range of the sensor and 
associated electronics.

Truman

schrochem wrote:

>Interesting read Paul. I was just wondering what advantage this has 
>over just using "filters" in Photoshop? 
>Now to pose a question I have been wondering about: if a sensor were 
>made specifically for B&W, what would be changed?  Admitedly a novice 
>in this area, I am merely thinking out loud here.  If we knew what 
>would be changed perhaps there is a filter set that can be used 
>to "alter" what the sensor sees.....which I guess was the reason for 
>your email, LOL. I guess I was thinking more along the lines of 
>a "standard" filtration set for most B&W situations instead of 
>fiddling around with different filters for each shot.
>
>Scott
>  
>

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