Visible Light Spectrum and Vision

• Visible light is defined as wavelengths between 380 nm and 780 nm.
• Peak sensitivity is at 555 nm and is determined by L and M cone spectral sensitivities, peaking at 570 nm and 543 nm.
• Some insects can see light from wavelengths 380 to 370 nm.
• The cornea absorbs light less than 350 nm, and the lens absorbs light less than 410 nm to protect the retina.

Color Wavelength Details

• Red ranges from 630 - 780 nm.

• Orange ranges from 590 - 630 nm.

• Yellow ranges from 560 – 590 nm.

• Green ranges from 490 – 560 nm.

• Blue ranges from 450 - 490 nm.

• Violet ranges from 380 - 450 nm.

• Indigo covers a very narrow range between blue and violet.

• Infrared light is above 780 nm and is not within the visible spectrum.

• Ultraviolet light is below 380 nm.

• The eye is still very sensitive to IR and UV wavelengths even when they cannot be seen.

Photopic vs Scotopic Vision

• Photopic vision is for well-lit conditions and allows color perception with cones.
• Scotopic vision is monochromatic for low light levels.
• Cones are not functioning at low light levels, so scotopic vision involves rods instead, giving no color perception.

Levels of Light

• Color discrimination is best at photopic levels, with luminance above 3.0 cd/m².
• Some loss of color discrimination occurs at mesopic levels (0.001 to 3.0 cd/m²).
• Color discrimination is further reduced at scotopic levels of less than 0.001 cd/m², with primarily rod input.
• Humans see differently at varying light levels.
• High light levels during the day (photopic vision) involve cones processing light.
• Very low light levels, like moonless nights without electric lighting (scotopic vision), use rods to process light.
• Both cones and rods support vision levels at many nighttime levels.
• Photopic vision has excellent color discrimination, while colors are in-discriminable under scotopic vision.
• Mesopic vision falls between photopic and scotopic extremes.
• Ambient light at night can be enough to prevent true scotopic vision.
• The human eye utilizes three cone types to sense light in three color bands.
• The biological pigments of cones have maximum absorption values at roughly 420 nm (blue), 534 nm (bluish-green), and 564 nm (yellowish-green).
• Cones overlapping sensitivity allows vision throughout the visible spectrum.

Attributes of Color

• Color appearance has three basic attributes, including hue, saturation, and brightness.

About Hue

• Hue perception arises from the combinations of four hues, these include blue, green, yellow, and red.
• These four colors have been classified as unique colors.
• They are organized in two pairs, red-green and blue-yellow.
• Hues do not look reddish-green or yellowish-blue.
• Red and green are in opposition, as are blue and yellow.

Hue Discrimination

• Wavelength discrimination can be described as the amount of wavelength change required to notice a difference in hue when lights are at equal luminance.
• Hue discrimination is not constant over any particular range of wavelengths.
• It is best at 500 nm in the Blue-Green region and at 600 nm in the Yellow-Orange region.

Saturation Defined

• Saturation can be described as the vividness of the color.
• The saturation scale varies from very saturated color (very little white) to completely desaturated color (i.e., white).
• Adding white light to spectral light desaturates/pastels color.
• Saturation is higher at short and long wavelengths relative to wavelengths in the yellow-green wavelengths under equal luminance.
• Saturation discrimination is often determined by the minimum luminance of spectral light necessary to make white appear noticeably different while keeping luminance constant.

About Brightness

• Brightness is the perception of the light intensity.
• Measurement of brightness is challenging because it is a perceptual phenomenon influenced by viewing conditions, state of adaptation, surrounding light, and the immediate surround of the target.

Variation of Hue with Intensity

• The Bezold-Brücke shift involves hue perception changing with light intensity.
• As intensity increases: spectral colors shift more towards blue (if below 500 nm) or yellow (if above 500 nm).
• As the luminous intensity of any particular hue decreases, vision becomes achromatic.
• This is associated with the Purkinje Shift phenomenon from dark adaptation
• The Purkinje effect causes the peak luminance sensitivity of the human eye to shift toward the blue end of the color spectrum at low levels as part of dark adaptation.

CIE Color System Defined

• The first stage in translating optical radiation into color perception is the absorption of photons by the photopigment in the cone outer segments.
• Once a photon is absorbed, the cone's response is independent of wavelength.
• The number of photons absorbed, not the wavelength, determines cone responses, which is the principle of univariance.
• Two lights differing in spectral composition may look identical if the cone responses to both lights are identical, which is called metameric match.
• The test wavelength fills the top part of a bipartite field.
• The bottom portion has red, green, and blue primaries.
• The amount of the three primaries (rλ, gλ, bλ) is adjusted to make a perfect match with the test light.
• One of the primaries may be used as a desaturant combined with the test light for an identical match between the stimulus field's halves.
• Primaries are usually in the short, medium, and long wavelength regions and are often called red, green, and blue.
• Matching all colors by the appropriate amount of three primaries has led to a color specification system based on color matches.

CIE Standard Observer System

• The figure shows the relative amounts of the 3 primaries required to match each wavelength are listed on the x-axis.
• These results are from the International Commission on Illumination (CIE) standard observer system.
• The tristimulus value is the amount of each primary needed to make a color match.
• Negative tristimulus values indicate the primary was used as a desaturant.
• Negative rλ values for 450 to 550 nm are indicative the amount of rλ had to be added to the test light to obtain a match with the other two primaries.
• RGB color matching functions were transformed to eliminate negative numbers and have one function identical to the human spectral brightness sensitivity function.
• The three primaries, called X, Y, and Z, are mathematical transformations rather than actual lights of R, G, and B primaries.
• The relative amount of the 3 primaries should not change with brightness if there is no photopigment bleaching, color specification can be simplified by applying/converting the tristimulus values into chromaticity coordinates.

Chromaticity Coordinates

• Chromaticity coordinates are designated as lowercase x, y, and z.

• They calculated from the tristimulus values for a given light.

  • x = X / (X+Y+Z)
  • y = Y / (X+Y+Z)
  • z = Z / (X+Y+Z)

• x + z + y = 1

• CIE's chromaticity diagram showcases that This conversion allows the results to be plotted in a two-dimensional system.

• Relative amounts of primaries must be used to make a color match.

• Spectral locus refers to the curved line, where the spectral lights (monochromatic lights) are located.

• All lights must fall either on or within the spectral Locus.

• The straight line between 400 nm and 700 nm is referred to as the line of purples

• Colors running along that line symbolize mixtures of 400 nm (blue) and 700 nm (red).

• Technically, CIE doesn't specifies the appearance itself/ It only specifies the relative amounts of the third, primaries required to obtain a match.

• The location to different colors within the diagram is a result of assuming that the observer is adapted to a neutral light and the light levels are representative of office lighting.

• A fundamental attribute of the CIE chromaticity diagram states that: If two colors mix, the colors are mixed together, the resulting color will lie on the line joining the two original colors/colours

• The color is created by mixing A with B, meaning it falls upon a straight line between two points and its location along such is determined due to relative amounts Of A and B

• If given the fact that more B is in the given mixture, then resulting color shall fall on the line closer to B

• Previously discussed The appearance of a specific colors' is specified by the three

• Basic attributes of colors' which includes : hue, saturation, and by brightness.

Excitation and Purity

• Due to CIE is not able to, specify the relative amounts of the primaries and brighness information gets lost. -Dominant wavelength and excitation can attempt to approximate the properties of hue and its saturation; however it can not be specified along an CIE diagram.

• With point C on 2D CIE chromaticity diagram = white light will only further illuminate this given colored objects.

• Chromaticity coordinates is set for the correct color (point F).

-Color F can also be the additive mixture between given wavelengths for pt D (487 nm) with C. (or any other colour for points that is found with these coords

• Because there is said dominant wlenght (487 n) in the previous statements. Hence, it can infer that the color is F) as itself can in face be is. As F contains hues of a hue of bluish.
• *When obtaining the dominant wavelength for pt. E), there does few more steps because The line that intersects) by expanding from whitelight that references, through E that intersects with line of the pupes that are usually located/found B that does contains no corresponding color ( wavelength
• *With this context) it does the line should be the opposite by following that this does spectral. Then its pt does can be located by(510 nm) A . (510 nm)

The wavelengths) at pts does are meant to follow an complemanty wavelength for color - L. With the previous statements if L (or any points with these given coords) are to be. With one or another. This can be achieved when there is match for reference ( white With a purple coloring, that can be the conclusion: the dominant wavelength is the complemant. For the main one itself

• (Pe) Excitation Purity is defined with an ratio with distance derived from the white stimilus that comes with distance from whites. To which is measured with WL'S.
• Wl will showcase with a, where the wl is. ( with the name of ab.
• This shows that the higher the wl / the color is at its PE states. When in other instances, with the PE color does get desaturated/ as the wl gets closer. -Color Vision Deficiency described, it it either lack of color distinction. Or that colors matches are made but outside the normal.

Color Vision Deficiency

• Mild, Severe, there differences depending on with in the problem / how difficult it will be

• *With CDV is that this can divided within as one Inherinted condition with another one that does is.

• Independent of which happens within an inheret. This can show up in system.

• Colorvision can be remained the same with/ stability through the life With Inherited condition

• Condition that does have visual asscoiated

• Conditon can progress with the

• *They less prevalent.

Congenital Color Vision deficiency

Congenital color vision deficiencies are classified as either red-green or blue-yellow depending on the colors it is likely to be confused with.
Red-green defects are X-linked recessive and relatively common, affecting approximately 8% of Caucasian males and 0.5% of Caucasian females.
Congenital blue-yellow defects are autosomal dominant with incomplete penetrance.
These defects are very rare, with a prevalence of approximately 0.1% in the general population, along with that for individuals with red-green defect (confuse colors) from L

And M cone. Another, for blue - Yellow (confuse wl's) from L +M and others...

More Vision def Types

• Vision def types includes trichromats, Dichromats, Monochromats. Another Normal and Anomauals... with 3 protanope, Tritanope, Deuteranope... Protanomalous, Deuteranomalou and others.
• Lines def show the wL def and it colors
• CTV test design/ can helps either with: Screen, Determine and or patient task. Task examples are CDV or others...
• CVD test can be performed through CTM, PT, TTs...

Color Vision Test

• Color matching test using HMC Oculus Anomaloscope Pseudoisochromatic Tests

Ishihara Test

• This edition comprises 25 plates with numerals of 1 color embedded in a background color of another color, with 13 plates. With The later shows and tells an path between XX that tells how def can happen.
• This tests is usually.
• The numeric tells its divisions, includes: demonstation and others.

Hardy, Rand

• This screens to test Y and RG colos, it attemps to grade the SD
• It contains a plate that shows its geom. Which is embedded with Dot
• The test includes 4 DT, Six screening plats (2 to make T def).
• The CV color plates is designed to detect an ,RG and or, with the sverity of T defect.

Kanon ColorDx(Adult Plates)

-PIp plates is computerzed plates plates that scrrens for all types of defs... AND diagnose svierity of the df, with that:

• IT test that follow ishi Plates

Threshold Plates ( Tests)

• Plate CCT this plate for computerized CUV tests THE test follow with C figu that tells S, h relative t0 rgre background.

   And it may be possible that ( G) ( can
  

  There for be followed... In which pt, what the gap is can tell its positions.

• *RCCT is to modulate all letter changed / is made ( Each color is select) Thattels the test that measures sc types ( for types to happen.

• CAD Test CAN test defiscnies through and that that discriminates gray or BOTH

• The CAD test is for the and it what comes from the and that discriminates as.

• *The individual squares change the luminous every ms so that sc looks as if/it is scintillating..

• With the squares is with L bottom

• In task to press appropate button that shows a correposnd direction of movement.

• FAM. It shows the CUV test in this to DO distngich from CN a CDV def

• C program also an c versn if there is subect to drag

• H types. HWA can be an c color Visito test def, or from navagational LT C.

• With these test shows to have green , and others.....