ZS20 Colour Contrast Tests


Testing Resolution with Different Coloured Backgrounds

The resolution chart developed by Dr J C Brown as described in his report here has rows of the letter E in red, blue, green, black, magenta, cyan and yellow, all on a white background.  As I found in previous testing using different camera models (FZ35/38, SD700, SD800 and ZS20/TZ30), the resolution varied depending on the colour of the E against the white background.  For example, the resolution of the yellow and cyan Es tended to be lower than the resolution of the black and red Es when against a white background.

I carried out tests with my ZS20 to determine how the colour of the background influenced the resolution and rendition of different colours of the Es.  I used the same setup as before (described here) but using prints of the chart with various different fill colours for the background instead of white.


Below are central 100% crops from the chart board with two different sets of background colour charts (click on an image for the full view):

Above: Chart board 1

Above: Chart board 2

From the above charts I constructed a table of resolution (in LPH) for each of the colour backgrounds.  The table is shown below.  High resolution values (above 2025 LPH) are shown in red (click on the image for a larger view):

It was obvious from the results that visual contrast was an important factor in predicting whether Es of a particular colour would yield a high or low resolution with a particular background colour.

I constructed a table from online sources which provide calculators for determining the visual contrast ratio of coloured text on a coloured background according to international standards for webpages, the Web Content Accessibility Guidelines (WCAG) 2.0, shown here.  The calculator I used is given here .

The table, shown below, gives the calculated visual contrast ratio for each of the background colours that I tested (click on the image for a larger view):

Comparing the resolution table with the contrast ratios table above showed that in most cases, a high contrast ratio corresponded with a high resolution of the Es.  For example, 100% black Es on a white background (or v/v) has a contrast ratio of 21.0 and gives a high resolution; while yellow Es on a white background has a low contrast ratio of 1.1 and gives a low resolution.

However, the contrast ratio does not always successfully predict the outcome for resolution.  I've marked with asterisks in the table five contrast ratio values which demonstrate this.  For example, cyan Es on 100% magenta or on 100% yelow backgrounds give a high resolution but the contrast ratios are low.


From the results I have summarised below the colour combinations which perform best and those which perform poorly in terms of resolution:

Combinations giving very good resolution:
Red on cyan, or white, or yellow, or pale grey
Green on dark blue
Blue on cyan, or white
Magenta on white, or pale grey, or yellow
Cyan on dark blue, or black, or dark grey

Yellow on dark blue, or black, or dark grey
Black on white, or green, or pale blue, or pale grey, or cyan

Combinations giving poor resolution:
Red on dark blue, or magenta, or mid grey
Blue on black, or dark grey
Green on pale blue, or cyan
Magenta on red, or mid grey
Cyan on pale blue, or green
Yellow on pale grey, or white
Black on dark blue

On the following page I have suggested a possible explanation for the observed variations in resolution.

Continue to A Possible Explanation

Return to ZS20 Resolution Testing Part 3

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