The photographs were taken in shaded daylight on a patio between a two story red brick block of apartments and some high sycamore trees. The sun was shielded by clouds for the most part.
I was initially concerned that the Automatic white balance setting might struggle in these conditions to produce reasonably accurate colours. However, when I used a grey card to set a specific white balance for the conditions I noted no discernable difference between the automatic and specific white balance setting. These photographs were taken with the white balance set to automatic.
No processing adjustments were made to the white balance or exposure levels of the photographs. The only adjustments made were to remove dust spots and to sharpen the images.
The images are ordered by exposure steps from dark to light -1, -0.5, 0, + 0.5, + 1.0:-
Image 1: Strawberries exposure adjustment -1.0
Nikon 70-210 mm at 210mm: Iso 400 f/32 at 1/15th
Image 2: Strawberries exposure adjustment -0.5
Nikon 70-210 mm at 210mm: Iso 400 f/32 at 1/10th
Image 3: Strawberries No exposure adjustment
Nikon 70-210 mm at 210mm: Iso 400 f/32 at 1/10th
Image 3: Strawberries exposure adjustment + 0.5
Nikon 70-210 mm at 210mm: Iso 400 f/32 at 1/5th
Image 3: Strawberries exposure adjustment + 1.0
Nikon 70-210 mm at 210mm: Iso 400 f/32 at 1/2
I noted some potential shortcomings in the way that I did this exercise:-
- The globular shapes of the strawberries means that there is a significant variation in tone across the surface of the strawberries. A flat coloured surface would have been better.
- Daylight was varying as clouds shielded the sun. This difference in light I believe explains the apparent anomaly that the exposure times for images 2 and 3 are the same.
- The colour of the strawberries also varies slightly.
Comparing the five photographs side by side in Lightroom, I gained the impression that the red hue in the darker two photos had a slightly bluer cast, whereas the red hue in the lighter two photos had a slightly orange cast. This rather contradicted my understanding of the theory from reading the notes that exposure levels should only impact the brightness, not the hue of the colour.
I used the "Colour checker" tool in Photoshop Elements to find the hue, saturation and brightness parameters for the colour of a point on one of the strawberries for each of the photographs above. The results for images 1 and 5 above were as follows:-
Image 1: Hue 1 degree Saturation 75% Brightness 26% (Red 26% Green 7% Blue 7%)
Image 5: Hue 2 degrees Saturation 74% Brightness 56% (Red 56% Green 16% Blue 15%)
Whilst the individual measurements were quite sensitive to the position of the point selected, I did my best to select points from the same area of the strawberry at 100% pixel scale. The trend of the 5 results were quite consistent:-
- In the 360 degree colour wheel used in the software, pure red would seem to be 0%. The hue measurements ranged between 358 degrees and 2 degrees which indicated that the colour selected was close to a pure red hue.
- The saturation was in a close range between 74% and 77% for the five different exposures. This confirmed the principle that changing exposure does not technically change the colour saturation.
- Brightness changed progressively from 26% in image 1 to 56% in image 5.
The colour checker was also useful as a way to see the difference between saturation and brightness for a selected hue. By selecting Hue in the colour checker box, the square box alongside displayed the range of saturations along the horizontal axis and the range of brightness along the vertical axis for the hue chosen. By moving the selection point in a vertical directions, the "before and after" box gives a side by side comparison of the brightness of the two points. In the same way, the effect of changing saturation could be compared by selecting two points in a horizontal direction.
In addition, I used the colour checker to test my initial visual impression that there was a slightly blue cast in the strawberry colour when underexposed and a slightly yellow cast when overexposed. I compared the tones side by side and acknowledged that the tones were in fact the same. My perception of colour is clearly rather unreliable. I wondered whether this could be linked to the fact that going from red towards purple around the colour circle, the saturated colours become darker in tone, whereas going from red towards yellow, the saturated colours become lighter in tone. I subconsciously maybe associated the darker shade with a bluey tone of red, and maybe associated the lighter shade with a yellowy tone of red.
I found it quite difficult to envisage the distinction between saturation and brightness until I used the colour checker. In the course of thinking about this, I was interested in various different ways of mapping or defining colours on screen. So far, I have come across three different methods:-
- Individual hue parameters (RGB, CMYK): Three or four main hues are defined with a separate parameter for each one. Saturation and brightness are governed by the intensity of the colours. Pure white is 100% for all parameters. In RGB, black is 0% for all parameters.
- Hue as single parameter (HSB): All of the hues are contained in a single parameter, in effect a color wheel of 360 degrees. The saturation and brightness are each individually defined by a separate parameter for any tone selected.
- Tone as a single parameter (LAB): All the tones from darkest to lightest are contained in a single parameter (L channel). Hues are split into two subsets blue - yellow in channel A and green - red in channel B. The mid point in A and B are neutral grey (representing zero saturation of both colours?).
I assume each methodology was developed for a particular purpose or type of user. It may be interesting to read Michael Freemans book "Colour" or equivalent in future.
.jpg)
No comments:
Post a Comment