Resolution measurements - TZ30 (ZS20) - Many images

Started Apr 3, 2013 | Discussions thread
Ianperegian
Senior MemberPosts: 2,451
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Re: Some further tests
In reply to Detail Man, 11 months ago

Detail Man wrote:

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:

https://docs.google.com/viewer?a=v&q=cache:fE3ikw9gwl8J:citeseerx.ist.psu.edu/viewdoc/download?doi%3D10.1.1.72.1595%26rep%3Drep1%26type%3Dpdf+spatial+perception+color&hl=en&gl=us&pid=bl&srcid=ADGEESiEyEcJR63juyk_QFqfdDfJSBpP9x4wKDJStnpeEOV7MvQqKawMBKl8Q6aNcQrKdt1zE8oYq29TUfb9NlJ7KeZZEP0BE2tQRiGEW8MHwgpR7n4mVBwiKWvMw25D_YuLcQt7xrDE&sig=AHIEtbRPmdPPz2nGNLErR21tMYeUPdg1Yg

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):

http://jp.physoc.org/content/359/1/381

... leading to:

http://jp.physoc.org/content/359/1/381.full.pdf+html

... and the original PDF link:

http://jp.physoc.org/content/359/1/381.full.pdf

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

http://www.perceptionweb.com/abstract.cgi?id=v070290

Thanks, Detail Man for those very interesting links.

The first link about half-tone images could also be said to be related to the way people perceive "noise" in images.  The analogy with the way people respond to pointillist paintings is interesting too.   The other links which give some insights into the physiology of human vision in relation to pairs of adjacent colours with high contrast such as red-green and yellow-blue and are also very interesting.

My reason for choosing the "visual contrast ratio" to compare with the results from Jimmy's charts was that it seemed to encapsulate the human vision aspects relating to viewing coloured text on backgrounds of different colours and with different contrasts and therefore seemed pertinent to the coloured Es charts.

There is quite a lot of information available about how the algorithm for calculating the visual contrast ratio was arrived at, and as might be guessed, ultimately there was a "committee" behind it.

As noted on this site: http://www.paciellogroup.com/resources/contrastAnalyser :
"Determining "colour visibility" is based on the Contrast Ratio algorithm, suggested by the World Wide Web Consortium (W3C)", and links are given there to further information.

This site also has a range of links relating to visual colour and contrast:
http://accessibility.umn.edu/color-and-contrast-414.html .

As I noted in my post above, it seemed that although visual contrast was generally a good indicator for predicting high or low resolution, there were several instances where a low contrast ratio was associated with a high resolution for particular coloured Es.

I have suggested that optical crosstalk on the sensor may be a an important factor relating to the poor resolution for certain colours.  However it may be that there are other factors responsible.

I'm inclined to think that the demoaicing process can't be a major factor because I tested my Panasonic SD800 camcorder using Jimmy's chart and it gave the same pattern of low resolution for the same particular colours.  Since that camcorder does not have a Bayer sensor there is no demosaicing, and yet it gives the same colour resolution pattern as given by Bayer sensor cameras.

I think the advantages of Jimmy's charts are that they provide a simple and reproducible way to compare the colour resolution from different camera systems.  I think this is something new, because all the camera review sites tend to examine only the "black adjacent to white" resolution, whether by the standard narrowing lines B&W charts or by MTF measurements on B&W sloping lines.  In actual practice, I don't think there are many people who confine their digital photography to only shooting in B&W.

I'm therefore surprised that there hasn't been more interest in Jimmy's charts, even though he has made them freely available.  They offer the only simple way, as far as I know, for the colour resolution to be easily determined as well as the B&W resolution.  I think colour resolution is a very important aspect of IQ but it seems to have been overlooked.

Ian

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