A Possible Explanation


A Possible Explanation for the Observed Colour Resolution Differences

It seems that optical crosstalk is a possible cause for the observed low resolution for certain colours of the Es when against particular coloured backgrounds.

For digital camera sensors, optical crosstalk results in poor resolution and colour mixing, and tends to worsen as the pixel size becomes smaller.  Optical crosstalk is explained here.

An article which discusses optical crosstalk in relation to CMOS sensors can be viewed here.

I calculated a measure of pixel size (the sensor area per pixel) from the data given by DPR for various camera models, as shown in the table below (click on the image for a larger view):

The Panasonic FZ50 and the models listed below it in the above table have now all been tested using Dr J C Brown’s coloured Es charts.  In all cases these models show a similar pattern of resolution for the different coloured Es, such as the low resolution of yellow Es on a white background.  These models use CCD, CMOS or 3MOS sensors and use Bayer or non-Bayer pixel arrays.  The only common factor is that they all have pixel areas smaller than 4 sq microns.

Dr J C Brown has kindly provided me with a crop from his recent chart test image from the listed Canon DSLR in the table.  This model has a full frame sensor with very large pixels (41.1 sq microns). What is very notable is that this chart shows very good colour rendition and resolution of all the coloured Es. The image is copied below (click on the image for the full sized view):

Above: Chart image crop from Canon 5D Type II (by J C Brown)

This seems to support the conclusion that optical crosstalk, which is associated with small pixel size, is a major factor in the poor colour resolution observed for the camera models with smaller pixels.

These tests were discussed in posts on the DPR Panasonic Forum, at:

http://www.dpreview.com/forums/post/52097341 and http://www.dpreview.com/forums/post/51413807.

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