Resolution measurements - TZ30 (ZS20) - Many images

Started Apr 3, 2013 | Discussions thread
Detail Man
Detail Man Forum Pro • Posts: 16,707
Re: Some further tests

Ianperegian wrote:

In collaboration with Jimmy, I have done some further tests with his original Es chart printed with a range of different coloured backgrounds.  I used my ZS20 with the same testing procedure as before.  The aim was to see the effect on resolution and colour rendition of the various coloured Es when adjacent to different background colours.

Below are central 100% crops from the chart board with two different sets of background colour charts:

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:

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 calculator I used is given here .

The table, shown below, gives the calculated visual contrast ratio for each of the background colours I tested:

Comparing the resolution table with the contrast ratios table 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

A Possible Explanation

It seems that optical crosstalk is a possible cause for the observed low resolution.  This is discussed in the following post.

Characteristics of human visual perception may well be a factor.

It is well known that the capability of the human visual system to distinguish different colors drops rapidly for high spatial frequencies.

Section 2.1, Perception Model at:

One study which directly compares luminance-contrast sensitivity with chromatic-contrast-sensitivity. That can be found in Contrast Sensitivy to Chromatic Gratings, The Chromatic Contrast Sensitivity Function section (on Page 389), and through the end of the paper including the Discussion section.

The final (full) paragraph on Page 393 summarizes findings, indicating that tested human visual response to a Red-Green grating (as compared to a White-Green grating) and to Blue-Yellow grating (as compared to a White-Yellow grating) was reduced in response by an (approximately) three-to-one ratio. The study appears to have implemented comprehensive, controlled methods.

The original web-link with Abstract (February 1, 1985 The Journal of Physiology, 359, 381-400):

... leading to:

... and the original PDF link:

I also found a more recent (2007) published paper reporting on a similar study. Abstract only at:

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