Colours into tones in black-and-white

I used the following picture which has objects with relatively high saturations of red, yellow and green on a bright blue background.

Colour image for conversion to black-and-white

Nikon 18-70mm at 70mm: Iso 200 f16 for 1.1 seconds

I explored the conversion process and adjustments in both Lightroom (version 1.5.1) and Photoshop Elements 7.

• Lightroom "Grayscale" tool has eight sliders each of which adjusts the intensity of a specific hue. Photoshop Elements, on the other hand, is less selective with just three sliders for RGB and one for Contrast. As a result, in Elements it was less straightforward to selectively adjust the "yellow".
• Photoshop Elements also has some interesting preset profiles for conversion to black-and-white which I used when doing the Elements of Design section of the course. At that time, I chose one of the presets by going through the different profiles to see what was the effect on the resulting picture. Whilst I understood the idea that colour adjustments will affect the black-and-white tones I did not further tweak the preset profiles as I did not like the results when I attempted this.

Conversions using Lightroom

I set out below the conversions of the above photograph using the basic grayscale conversion and three others where I adjusted a different colour in turn.

Basic conversion without colour adjustment

As might be expected the red tomato and blue background are relatively dark in tone as these were both highly saturated colours. The lemon and lettuce leaf by contrast are lighter as these were brighter less saturated colours.

Conversion with additional blue

There is a market lightening of the background, as would be expected. There are relatively minor changes in the tones of the red, yellow and green objects, which quite surprised me after my experience of using the RGB sliders in Elements.

Conversion with additional yellow

The additional yellow makes the mid-yellow and yellow highlights slightly brighter relative to the other colours. The yellow shadows have not changed as much. When viewed side by side with the general greyscale conversion, the red of the tomato has also lightened slightly. Presumably, this is because in RGB system, yellow is created by mixing red and green.

Conversion with additional red

Surprisingly, increasing the red only appears to have lightened the tomato and neither the yellow nor the green appear to have changed to any significant extent. In the RGB system, red is a significant component of yellow and green hues. Therefore, both yellow and green might have been expected to change if strength of red is increased. (Compare this with changing Red channel in Elements - below.)

It is noticeable that the bottom and right hand rim of the tomato have remained dark. The shiny skin of the tomato in this area is likely to be reflecting the blue surface which is not being changed as red saturation increases.

Conversions using Photoshop Elements

As the colour sliders in Elements adjust the R, G and B channels, I checked first what were the RGB levels for the four main objects in the photograph using colour checker tool. The proportions of each channel in a bright part of the objects were as follows:

Percentages R G B

Background (blue) 3 35 64

Tomato (red) 73 27 0

Lettuce leaf (green) 38 47 14

Lemon (yellow) 46 41 13

On this basis, my expectation was that increasing red, for example, would impact the black-and-white tone of the tomato, but it could also modify the tone of the lettuce leaf and lemon as red channel is a significant contributor to those colours. Increasing green on the other hand could potentially impact the tones of all of the objects.

This was indeed what I found. Increasing the red channel, not only increased the brightness of the tomato, but it also increased the brightness of all of the colours except the blue background. In fact the yellow and green highlights became completely blown out, and I needed to reduce the contrast slider to bring the tonal range back to a median position. This is a major difference with the Lightroom adjustments where the sliders affected a specific hue only. Other colours and the overall tonal range were not affected.

Conversion using the Elements "urban shapshot" preset

I chose the "urban snapshot" preset for black-and white conversion as a reference for the other colour variations I made. This was the most "neutral" of the presets for the bright colours in this photograph.

Conversion with additional red

In Convert to Black-and-white adjustment box, I increased the Red slider a short distance from 60 to 81. I could see the highlights were already blown out, so I reduced the contrast to -12 from 0. The net result is that the tomato is much brighter relative to the background than it was. The shadows on the underside of the tomato have almost totally disappeared. The other fruit are also much brighter, but the shadows remain. Another unexpected change is that the reflection under the lettuce leaf is much brighter. The blue background has become dark grey.

Conversion with additional yellow

As there are only Red, Green and Blue sliders in the Elements Conversion box, I increased both the red slider and the green slider equally by 20. As I explained above, I was aiming to follow the proportions of the yellow colour, which was almost equal amounts of red and green with a much smaller proportion (about 13%) of blue. The effect was to drastically increase the brightness, and I needed to reduce the contrast by 40.

The appearance of the objects in the picture has changed significantly. The background is a similar mid-tone to the urban snapshot reference. The items of fruit are significantly brighter. The tomato has lost the shadows on the right side and underside away from the direction of light. Also the shadows of the fruit on the background have diminished in intensity.

Conversion with additional blue

Following the same thought process that I used for increasing yellow, the blue in the background comprised about 64% pure blue and 36% green according to the measurements that I noted above. Accordingly, in the Elements conversion box I increased blue and green in the proportion of roughly 2:1, green from 28 to 38, blue from 12 to 46. As before, I reduced the contrast to prevent the hightlights from being blown out.

The effect has been to reduce contrasts and shadows so that the blue background, tomato and darker areas of the lettuce leaf and lemon and a similar mid-grey.

Conclusions

This exercise has been instructive for several reasons:

• Adjusting colour saturation during conversion to black-and-white is a valuable tool to control the balance of tones in producing a monochrome picture.
• Lightroom and Elements seem to have a fundamentally different approach in the modules for conversion to black-and-white. In Lightroom, the controls seem to allow selective control on a hue by hue basis. In Elements, the three RGB colour controls affect items in the picture in a much less predictable way. The effects can simultaneously change a range of colours in the photograph. Potentially, this is more difficult to control.
• Elements has a number of preset conversion settings which produce quite a variety of different effects, e.g. infra-red, press. I found that these provide a useful variety of settings for many situations when I used these when I converted my photographs into black-and-white for the previous assignment and exercises.