In my previous wet film life I enjoyed shooting B&W which I processed in my darkroom but I was never much of a fan of 'on camera' filters. I preferred to work on the prints in the darkroom but this exercise has shown me just what I might have been missing. Certainly the effects of colour filters on tones of grey are considerable but I am glad that I can apply these effects digitally in post production rather than having to work them out beforehand.
For a digital photographer the exercise asked us to shoot a single still life that displayed the primary colours of Red/Blue/Green plus the additive colour yellow thrown in. We were then asked to apply in post production a Black & White version plus an additional version of Black & White with Red, Blue, Green and Yellow filters applied. In Photoshop this is achieved by selecting Image/Adjustments/Black and White and then moving the appropriate colour slider.
We were also asked to shoot the image in an appropriate format such as JPG so that RAW processing wouldn't affect the initial image. In addition our exposure settings should be suitable for a neutral grey which I did separately.
So my 18% grey card shot looked like this...
... which looked like this on my camera back.
As you can see a manual setting of 100/f8.0 at ISO400 gave a nice middle of the road exposure for the grey card as can be seen on the histogram.
Under the same light conditions I shot my colourful still life in JPG format.
The rest of the exercise relied on Photoshop and the first change I made was to move the image to Black & White using the average Default settings. These were not as I expected with all colours at Zero but ran as such...
...with the final result looking like this.
I then set about changing the slider setting to simulate the RGBY colour filters but I did this in two ways. Firstly I manually set the sliders to emphasise a particular colour and then I tried again using the pre set Photoshop filter settings. They looked like this:
RED MANUAL SLIDER
Here I brought the red up to around 120% and reduced the other colours to near zero but ensuring that the textures were still clearly visible. The Red Bournville chocolate wrapper has turned almost white but the rest of the colours remain fairly unaffected except the area of the yellow sweet which had some red reflection on it as it lay close by.
RED PRESET FILTER
The big difference between my efforts and the Photoshop standard is that it raised the yellow bias to 120% whilst reducing the cyans to -50%. This has resulted in an unwelcome brightening of the yellow hue and an overly dark blue hue.
GREEN MANUAL SLIDER
The green slider had the expected effect of brightening the green hue but this change is not as impressive as the red example earlier. The green shade of grey was a mid grey in the first place so the alteration has not been so dramatic. I could have emphasised the effect further but this would have been at a loss of detail through overexposure. The darkening that I made to the other colours, however, has helped to single out the change to the green sweet.
GREEN PRESET FILTER
The pre set filter has again had the unexpected effect of raising the amount of yellow as well as green, which has been lifted less than I did to only 90%. The yellow was raised to 120%. This green increase is only up 50% from the standard B&W conversion. I am beginning to realise that these pre set amounts are probably based on a nature photograph where it would look unnatural to have grass and leaves at such a light shade. Why the yellow should be raised for a green filter escapes me at the moment.
BLUE MANUAL SLIDER
Here the blue hue has had a slightly more dramatic alteration from its original shade than occurred with the green. I was able to play with two sliders to obtain this effect and found that the cyans slider had an excellent brightening quality and although I also raised the blue slider I didn't move it as much to ensure that the texture of the sweet wrapper remained.
BLUE PRESET FILTER
The blue preset filter raised both blue and cyan to 110% and reduced Red, Green and Yellow all to 0%. This has the effect of really emphasising the blue sweet whilst rendering the others down almost into the blacks, particularly for the red and yellow hues.
YELLOW MANUAL SLIDER
As expected the yellow sweet had brightened nicely, except for the areas which showed a red reflection from the adjacent red sweet.
YELLOW PRESET FILTER
Here the Photoshop pre set effect has increased the red slider as well as the yellow and brightened both hues. This was another unexpected result.
In conclusion... it is clear to see that the manual use of the sliders can individually brighten (or darken if required) the basic primary and additive colours. Used in combination it is possible to alter the brightness of almost any colour. The pre set filter options that Photoshop provides do much more than altering an individual colour but may be more suited to an overall scene.