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The degradation that accompanies a reproduction is notoriously vital for the human skin’s colour. The development of the colour TV had to face this problem when standardizing the fosfors for the primary colours. Initially, in the NTSC and PAL systems, the reproduction of the skin appeared more saturated with a slightly yellow overtone. Subsequently there was a shift towards the green-blue tone. The various techniques proposed over the years have tried to yield to the majority of viewers. In general one tends towards “colourfulness”.
For example, we prefer a tanned face rather than a pale face but the preference is always subjective and personal. In some systems the cromacity can be adjusted so that anyone can find his/her own persional version of fidelity.

It is known that the source’s spectral composition that illuminates an object alters the colour aspect of the object itself. For example, a colour photograph can tend to red or green tones depending on whether the object was illuminated by an incandescent or neon lamp. Various authors have proposed mathematical methods to correct the effect as done in photo copiers, thermal and inkjet printers and in lithography. In short, the image is corrected taking into consideration how it may appear under another type of luminosity. The typical case is that of the paper copy of an image generated on a phosphor display. To equalize the colours that appear on the printout, the colours must be corrected before the image is sent to the printer.

Art 2/8 - Related article: The difficulties with reproducing the colour of the skin (part 1)

Mistrust towards the “reproduction” and the awareness of its fidelity limits are enclosed, for example, in the question to whom had the opportunity to meet, say, a TV star: better or worse when seen in person?

On the other hand it is known that not everybody uses the same yardstick when evaluating the degradion of an image. As Wright notes (The Rays are not Coloured – A.Hiler, Bristol 1967), in a family there is always one member who wants to adjust the “optimum” view from his/her point of view.

Wright reminds of the discussions that took place at the BBC, in the times before colour TV, when one wondered whether it was more important to tune the B/W or colour image..

Besides that, Wright comments the fact tht his wife exclaims “how perfect are the images on this TV set” almost always when the close-up of a face is shown.

Certainly some precision is lost during transmission but the quantity of details necessary to reproduce colours is within the televison system’s capabilities and can show a “perfect” image on a domestic TV screen. We should also not forget that, according to a recent theory, (with reference to the days when Wright wrote that book) electrophysiological “sharpening” mechanisms come into play .

Naturally, when we go too close to the screen, the image may appear to degrade as the “sharpening” mechanism becomes less effective. Similarly, when the scene is complex, with so many details that they exceed the TV system’s capacity the visual mechanism cannot improve the image. The optimum, therefore, is when the TV’s capacity meets those of the visual system. But the problem of the quantification of the information content conveyed by the “message” of a work of art is still open.

Art 1/8

Over time, methods have been developed to measure the colours of a source.

These methods are, notoriously, based on calculations, starting from spectroradiometrics, or directly through the colourmeters based on the so-called colormetric functions, or last but not least, on the color temperatures.

Let’s briefly remember that the spectral distribution of the emitting power of a source contains all the information necessary to determine the chromaticity, the color temperature and the yield index of the source being examined.
After these measurements one proceeds with the colormetrical functions defined by the CIE 1931 and 1964 standards and calculations are made with the computer connected to the exit of the spectroradiometer. Modern spectroradiometers possess the required precision to define the standards.

Regarding the colormeters, let’s remember that they can be divided in two large groups: visual and photoelectrical.

The first is based on the extraordinary capacity of our visual system to establish when two stimula are identical or are slightly different.
They are based on the trichromatical components which permit us to determine the proportions of the three primary colors which, converted to the values of the CIE colormetrical components, lead us to the tricromatical coordinates of the source.

The operator using his visual capacity must be highly motivated. The sources to compare must be positioned next to each other and must be framed with other sources of the same type, creating a union of practically uniform luminosity. The background should be greyish.

It is advised to combine the observations with the colormetric data. Two sources of different spectral composition could be identical for one observer (normal) but not for another (also normal). Furthermore, the colormetric data of the source may show a similarity, as precise as we want, but that is not accepted by another observer.

The photoelectric colormeters produce electrical output for signals from different frequencies. These signals are proportional to the CIE X, Y, Z system, obtained using the calculation method. Very much known is the colorimeter of Barnes which achieves a precision of 0.003 for the X and 0.002 for the Y value.

Article 1/7

The closest point to which the oberver can converge is called the closest point of convergence. The patient is asked to focus on , for example, a pencil kept at a certain distance and to move it slowly closer to the eyes. When the limit is reached, we will see that the eye moves outwards and the patient starts to “see double”. A closest point of convergence of more than 10 cm is abnormal. If the patient has difficulties with this excercise, he/she can be asked to move a finger close to the eyes. Often this results in a closer point of convergence.
Higher precision is reached using a piece of paper on which a vertical line is drawn; it is fixed on a sleigh along a graduated stick. The patient tells when he/she starts to “see double” and, at the same time, the examinator observes the direction of the eyes. This tool takes the name of its inventor Livingaton.

From Optometria e oftalmologia by prof. Sergio Villani

“The mystery of the absence of blood vessels in the cornea and therefore its transparency - a fundamental requirement for the eyesight - has been for 50 years a subject of scientific research. This peculiarity has made it an experimental platform used to validate pro- and anti-angiogenic substances, i.e., used to facilitate or hamper the formation of blood vessels.
Now our studies have identified the responsible for this phenomenon: the presence of high concentration of a proteine, the receptor Fit-1 - explains Sandro De Falco, researcher of the Istituto di genetica e biofisica del Consiglio nazionale delle ricerche of Naples and coauthor of a research in collaboration with the laboratories of Kentucky University of Lexington and the Medical College of Georgia (Usa) and researchers in Japan, the UK, Australia and Italy.

The researchers started off from the observation that initially seemed to be a paradox, i.e., in the cornea there is a large concentration of the Vascular Endothelial Growth Factor (VEGF).
This protein interacts with two proteine receptors, known as Fit-1 and KDR, able to transmit to the cells the signals activated by the VEGF. The Fit-1 receptor exists in two forms: a membrane able to transmit the signal and a liquid not yet anchored to the membrane. The key to the absence of blood vessels in the cornea is the presence of high concentrations of Fit-1 in liquid form and the absence of the membrane form.
To verify this hypothesis the researchers have worked with chemical and genetic approaches on various animals (laboratory mice) in which the expression of a single gene has been inhibited
“Using mice and knocking-out the Placental Growth Factor (PlGF) gene, belonging to the same family of VEGF and capable of interacting with the Fit-1 receptor, says De Falco, we have verified that also in our animal model, hampering the expression of this receptor, one obtains a spontaneous vascularization of the cornea. This test has been confirmed also using variants of the GPF proteines, generated by us.
A confirmation of the correctness of these experimental approaches used to identify the molecular mechanism has been confirmed in the cornea of the Trichecus Manatus, a walrus that lives near river estuaries. In the cornea of the walrus there is no liquid form of the Fit-1 receptor, but only the membrane which determines correctly the vascularization of the cornea - explains De Falco. “The possible benefit of our research will be the use of this molecule to hamper the formation of new vessels especially in tumors, principal cause for blindness of seniors”.

Source: Salute Europa of 26 October 2006

In exocyclovergency the superior part of the vertical meridian inclines, for both eyes, towards the temples; in incyclovergency, the same meridian inclines towards the nose.

The fusional amplitude in incyclovergency (positive cyclofusion) in a normal subject is of 8-12 degrees, while in exocyclovergency (negative cyclofusion) in the same subject it is of 7-10 degrees. The amplitude of fusional cyclovergency is more stimulated by people with vertical features than with horizontal features.

From Optometria e oftalmologia by prof. Sergio Villani

As a first step in computerized colormetrics it is necessary to know the coefficients of absorption and scatter of the deyes and materials. These data are, in substance, the factors that appear in the laws of Lambert-Beer and the equations of Kubelka-Munk. In short, one has to proceed with the so called “callibration of the materials”.

Then one proceeds with the calculation of the “first recipe” after having stored the spectral reflecting curve in various conditions: opaque material, transparent material, translucent material, printing on paper, etc…
In the case of highly glossy , one needs a measuring program that takes considers the item with and without gloss.

The computer contains the data regarding the various deyes with which the colour can be created on various materials (paint, plastic, linnen) and the conditions of dyeing. The choice is not automatic but determined by an experienced human being. An expert knows immediately 10 appropriate deyes which the computer can process considering 16 values of reflection. When the result with 10 deyes is not satisfactory, the number is increased and recalculated till we have the “recipe” of a colour with the same tricomatric components
(tristimulus values) of the sample.

Those data are sufficient for the computer to calculate the correct “recipe” within a certain tollerance (usually 0,1).

The calculation starts with an estimate of the concentrations necessary for the tricromatic components.
Then the concentrations are changed and one can see how the tricromatic components change with varying concentrations.
This serves as a guide for subsquent modifications of the concentrations till the sample and “recipe” match.

As we mentioned above, the equalization refers to certain light conditions. But certain programs allows us also to calculate the index of metamerism for other light conditions. During the calculations one can also see the costs for equalization if the costs of the deyes are stored. The process can be stopped when a given, maximum, cost is reached.

Related article: The computerization of colormetrics (1/2).

Colormetrics by prof. Sergio Villani.

As known there is also a fusional amplitude on the vertical plane; called positive when the movement is upwards with the right eye or downwards with the left eye; negative in the inverse way.

The fusional power on the vertical plane is significantlly inferior. In subjects that are considered normal variances of 1 to 6 prismatic diopters were found. When testing vertical movement one has to take in account the time left to the patient to relax the muscular contraction because it has been noted that, within the first 5 prismatic diopters, every 30 seconds there is an increase of 1 prismatic diopter. If, for example, in a subject one finds 1-2 prismatic diopters of vertical amplitude at a normal rithm, a repeated slower test one can arrive at up to 5-6 diopters.

From Optometria e oftalmologia of prof. Sergio Villani

In the modern industry there is a strong move towards the equalization of colours by computer, as well as the subsequent calculation of the colours needed to create that colour with the employment of measuring systems.

The types of computerized colourmetrics are numerous and still evolving. The advantage of computerized systems over traditional colormetrics are beyond discussion: precision is very high because avoidable errors can be minimized.

Computerized colormetrics starts on the 50s and is immediately used in the application of the law of Lambert and to resolve the equations of Kubelka-Munk.
It all started with graphical methods, then on to analogic computers, in which (manually) spectrophotometric data was stored. A very expensive large computer was used in 1970. Recently, instead, simplified spectrophotometrics are used. (abridged), with a PC (Personal Computer).

The conventional equalization required (and requires) highly specialized personnel that is not always available. Instead, computerized colormetrics can be bought and used by anyone. Furthermore, the computer is faster than the human operator, supplies a more economical recipe and with minimal metamerism to match the colour being processed.

In the case of human equalization, tests have to be performed, costing time and money. All this is reduced with computerization. As a rule, the “recipes” that emerge from the comparison, visual as well as computerized, are subject to progressive corrections in order to improve the equalization but the number of corrections

that are necessary are more in the visual case.

Colorimetrics prof. Sergio Villani.