WO2009004375A1

WO2009004375A1 - A device for contrast assessment

Info

Publication number: WO2009004375A1
Application number: PCT/GB2008/050520
Authority: WO
Inventors: Hilary Dalke
Original assignee: Hilary Dalke
Priority date: 2007-06-29
Filing date: 2008-06-30
Publication date: 2009-01-08
Also published as: GB0712610D0

Abstract

A portable device for assessing the contrast between two surfaces has a light source (18) for illuminating a surface and a colour sensor (17) both mounted on a handheld body (10), the sensor detecting light from the source and which has been reflected back from a surface under test. A processor (22) converts the sensor output into a colour space determination and then extracts from that the (5) light reflectance value Y of the illuminated surface, the Y values from at least two surfaces then being stored in a memory. The body (10) has a display (11) for immediately showing the difference between the Y values of a chosen two surfaces or of different areas of the same surface.

Description

A DEVICE FOR CONTRAST ASSESSMENT

This invention relates to a device for assessing the difference (contrast) in light reflectance values (the Y values within a colour space) of two surfaces, but which in a preferred form may also be used to assess the light reflectance value of a single surface relative to a datum, conveniently expressed as a percentage.

Building regulations and standards, accessibility guidelines and the British Disability Discrimination Act may require various critical surfaces both externally and internally of a building (and particularly a building to which the public has access), public transport vehicles, public spaces and environments all to have a certain minimum contrast difference between adjacent surfaces. This applies both to structures themselves, as well as components, elements and contents of the structures. Other areas where minimum contrast between adjacent surfaces may be required may include text on packaging for products, signage, street or pavement markings, stair nosings and treads and so on. This minimum contrast is required in order that the adjacent surfaces may have adequate visibility, especially for visual impaired and disabled people.

For example, a surround to a door in a wall of a care home where there may be people with impaired vision, and also the door handle on the door itself, may be specified to have a sufficient contrast to the door, in order to meet safety requirements. Thus, the regulations may specify that the difference in light reflectance values between adjacent or closely proximate surfaces (such as a door and door surround) should exceed a pre-set threshold. Further, the light reflectance value of a surface should not vary by more than a specified amount over that surface, or should have an average value of more than a specified minimum. This applies particularly for variegated surfaces not having a uniform reflectance, such as natural wood.

Apparatus such as colourimeters and spectrophotometers able to measure the colour and light reflectance values of a surface are well known for colour measurement and quality control purposes. Apparatus of this kind allows the assessment of colour in a so-called colour space within which the characteristics of colour and light reflectance values can be defined. Such apparatus is relatively expensive, difficult to use and relatively heavy, the apparatus is therefore not readily portable. Further, apparatus of this kind is somewhat over-specified for a simple light reflectance value determination and then a contrast evaluation. Consequently, it is very expensive to perform contrast evaluation tests on surfaces for example within buildings, on objects and other items (such as signage) and as a result such contrast evaluation tests are often overlooked, notwithstanding a requirement within the regulations for those surfaces to have minimum light reflectance and contrast differences, especially in buildings and other environments used by people with visual impairment.

The colour of a surface is perceived by the human visual system in a particular way which is not directly representative of the spectrum of light either emitted by or reflected from the surface. A ray of light having a given spectrum stimulates the three types of colour receptors (cones) in the eye by different amounts and it is the combination and analysis of these three stimulation levels by the brain that allows the surface to be perceived as being of a particular colour. From this, it will be appreciated that two lights with different spectra can appear to be the same colour - and that is why display screens with only three types of phosphor (and so of different colours) can be used to represent most of the colours that a human can see.

In order to specify a colour (i.e. a particular input to the human visual processing system, as distinct from a spectrum of light), only three numbers are required. These could correspond to the three stimulation levels described above for the receptors in the eye but for practical reasons - and in particular the difficulty in establishing the actual spectral response of human cone cells - colour is not normally specified in this way. In 1931 the Commission Internationale de I'Eclairage (CIE) defined the "CIEXYZ" or "CIE 1931 " colour space with the co-ordinates of X, Y and Z. For convenience, Y was defined to be the same as the luminance function.

CIExyY was then defined with x = X/(X+Y+Z) and y = Y/(X+Y+Z) where the Y value is the same as in CIEXYZ. This made a slightly more convenient colour space in which (x,y) specifies the chromaticity ("colour") of a light source and Y its brightness.

Other colour spaces are known, and mention may be made of the CIEL^*a^*b^*, CIEXYZ, CIExyY, RGB, CMY, CIELUV, YUV, YIQ, YCbCr, 11 1213, LSLM, UVW, HSI, HIS polar, HSV, HSV polar, LHC and LHS colour space systems. These have been developed for various reasons; some of these have been defined as functions of the (X,Y,Z) values in order to represent more accurately perceived differences between colours.

There is a subtlety that if the light source is a reflective surface rather than an emitting body, the apparent colour will depend on the chromaticity and brightness of the light illuminating the reflective surface. There is a standard technique of scaling the readings for brightness so that a perfect reflector has a Y of 100 and a CIE-specified D65 standard illuminant may be used to control the chromaticity.

The CIEXYZ and CIExyY colour spaces are fundamental to colour measurement and are well understood by those skilled in the art. As such, no further explanation of these colour spaces will be given here.

When a colourimeter is being used to determine the light reflectance value (Y value) of a surface, this is normally performed indirectly by calculating the light reflectance value from other measurements performed on the surface. Thus, the apparent reflectivity may be extracted from the colour space data determined for example by a colourimeter.

This invention aims at providing a relatively simple, easy-to-use, readily portable hand-held device primarily intended for assessing a difference (if any) in the light reflectance values of two surfaces, but which in a preferred form may also be used to assess the light reflectance value of a single surface relative to - A -

a datum, as compared to a "standard" surface, and further to average the light reflectance values of different parts of a single surface.

Accordingly, this invention provides a portable hand-held device for assessing a difference (contrast) in light reflectance values (the Y values) of two surfaces, which device comprises:

- a manually-grippable body;

- a colour sensor mounted on the body and comprising a light source for illuminating a given surface and a receptor to detect light emanating from the light source and reflected back from an illuminated surface, to provide an electrical sensor output;

- processing means contained within the body and to which the sensor output is supplied, the processing means being arranged to convert said sensor output into an appropriate colour space determination and then to extract from the colour space determination the light reflectance value (Y) of the illuminated surface;

- memory means for storing a plurality of extracted light reflectance values, the processing means being arranged to operate on a plurality of said stored values to provide a comparison signal; and

- output means mounted on the body and arranged to output said comparison signal thereby to indicate the difference in light reflectance values of the compared surfaces.

It is fundamental to the function and operation of the device of this invention that the difference in the Y value between two surfaces can be used to predict whether those surfaces can be distinguished by a person with visual impairment - for example one of the surfaces may be a door surround and the other surface the door itself. In order to obtain the Y value for each surface, a colour sensor provides an output which is processed into an appropriate colour space, and preferably either a CIEXYZ or CIExyY colour space, from which the Y value may then be extracted. The respective values of two surfaces may then be used to calculate a light reflectance value difference. In order to allow the construction of a portable hand-held device for this purpose, the body of the device contains a microprocessor which runs a predefined program contained in firmware, also within the body of the device. Further, the body contains a memory device (which may be on-chip with the microprocessor itself) for storing determined Y values so that the microprocessor may subsequently effect an average of a certain number values, if required, and a comparison between stored values.

The light source of the colour sensor may comprise any one of a light emitting diode, an incandescent lamp, a fluorescent lamp or a gas discharge lamp but most preferably one or more light emitting diodes are employed in view of the relatively low power consumption for a given brightness. The receptor of the colour sensor preferably comprises at least one photodiode arranged to receive light emanating from the light source and reflected from the surface under test. The combination of the light source and receptor may take one of several forms in order to achieve the required functionality. For example, a white light source could be employed with three photodiodes having differently coloured filters associated therewith, in order to give the correct spectral responses for measuring the X, Y and Z light reflectance values. In this case, the photodiodes may be associated with one or more dye-based RGB or CIEXYZ filters. Another possibility would be to use several coloured LEDs as the light source and a single photodiode as the receptor with a light reflectance assessment being performed by energising the LEDs in sequence.

The output of the or each photodiode may then be associated with one or more transimpedence amplifiers to produce the sensor output. The processing means conveniently operates on a digital basis and so the sensor output should be supplied to an analogue-to-digital converter, for subsequent conversion to the selected colour space.

In order to achieve the required functionality of the device, it is preferred for the processing means to include comparison means to determine the difference between two light reflectance values and then compare that difference with one or more pre-set criteria. For instance, a pre-set criterion may be an acceptable threshold value for the difference in light reflectance values, so that the comparison signal is indicative of an acceptable or unacceptable light reflectance value difference of those adjacent surfaces. The memory means allows the storage of extracted Y values. For example a variegated surface may require several separate assessments to be made on different parts of that surface and the Y value for each of those assessments is stored in the memory means. This may be achieved by including a manual control such as a push-button on the body of the device which when operated commits the instantaneously assessed Y value to the memory. A plurality of such values from a single surface may then be averaged for subsequent comparison. A further control such as a second push-button may be provided on the body for electronically notifying the processing means that subsequent assessments are on a second surface, for comparison with a previously stored Y value or averaged Y value. In the alternative, a longer depression on the first push-button may perform this function.

The output means may comprise a visual display device, such as a LCD display, a LED display, one or more coloured indicator LEDs or lamps or the like. Alternatively or in addition, the output means may comprise a sound transducer, for issuing sound samples or synthesised or pre-recorded speech. Further, the output means may include a data transfer arrangement, to permit the transfer of data from the device to an external electronic device such as a computer or a personal digital assistant. Such a data transfer arrangement may include a USB port, a RS232 port, a Bluetooth or other radio frequency wireless transmitter or an optical or infra-red communication link.

Calibration of the device of this invention may be performed by using the device with a pair of standardised surfaces, one having near perfect reflectance and the other having near perfect absorption (black). Such surfaces may be in the form of appropriately coloured tiles. The processing means should be set to a calibration mode and then the device is used with those surfaces in order to store in the memory means the extracted light reflectance values of those surfaces. These stored values may then be used for subsequent reflectance assessments.

In a preferred form of this invention, the body is configured to be sufficiently small for holding in one hand. The body could have an elongate form, so as to be a pocketable pen-like shape, or could be more rounded or bulbous but still pocketable. The colour sensor, comprising both the light source and the receptor, may be disposed within a chamber at the forward end of the body, the chamber having a small opening for placement on the surface to be tested. The wall of the chamber defining the opening is preferably compliant to some extent whereby the opening may conform to the profile of the surface on which the device is placed, thereby excluding essentially all ambient lighting. Further, the placement of the opening on a surface may serve to activate the device to perform a light reflectance value determination. So that the device may be easily portable, the body advantageously houses a self-contained power source, such as a single use or rechargeable battery. In the alternative, an external power source may be employed, connected to the device by an umbilical cord.

By way of example only, two specific embodiments of a portable hand- held colour contrast assessment device constructed and arranged in accordance with this invention will now be described in outline, reference being made to the accompanying drawings in which:

Figure 1 is an axial section through the device;

Figure 2 diagrammatically illustrates a docking station for the device; and Figures 3, 4 and 5 are respectively perspective, side and underplan views of a second embodiment of device.

The device shown in Figure 1 is a wholly self-contained colour contrast assessment tool designed for easy use, to establish the contrast of surfaces and more importantly between adjacent surfaces wherever a minimum contrast is required or has been specified. This may be within or externally of a building, its fixtures, materials, fittings and components, public spaces and environments, packaging for products, signage and so on.

The device comprises an elongate pocketable pen-like body 10 containing the components of the device and also a liquid crystal display (LCD) 1 1 for displaying the results of the assessment. The device has an opening 12 at its forward end for placement on a surface 13 to be tested and a pair of pushbuttons 14,15 to enable operation of the device.

Internally, a colour sensor 17 is mounted at the forward end of the tool, to look through the opening 12. That colour sensor 17 is associated with a white light source 18 and also contains a photodiode, dye-based RGB filters, a transimpedance amplifier and a current-to-frequency converter circuit to provide an analogue output signal, all on a single chip within the sensor 17. Power to the light source 18 is supplied along wire 19 and the analogue output signal is fed along wire 20 to a RGB-to-CIELAB conversion circuit 21 . A microprocessor and associated components are mounted on a circuit 22 also arranged within the body 10 and connected to the RGB-to-CIELAB conversion circuit 21 , firmware also being provided on circuit 22 in order that the microprocessor may run a suitable program to give the required functionality. The circuit 22 is also connected to the LCD 1 1 in order that the result of the processing may be displayed.

The output signal from the current-to-frequency converter of the sensor 17 typically is an analogue square wave signal. This is then converted to a digital signal and the microprocessor performs a conversion function for the RGB tri-stimulus values so as to obtain the Y value of the surface. The tri- stimulus values can be either additive or subtractive colorants (such as RGB or CMY), or made up of three attributes (such as lightness, chroma and hue) and include a selected one of the following: CIEXYZ, CIELAB, RGB, CMY, CIELUV, YUV, YIQ, YCbCr, 111213, LSLM, UVW, HSI, HIS polar, HSV, HSV polar, LHC, LHS. The body 10 defines a chamber 23 for containing a rechargeable battery, the adjacent end face of the device being provided with a pair of contacts 24 for recharging the battery.

Though not shown in the drawing, a switch arrangement may be associated with the forward end of the device, such that when the opening 12 is placed on a surface, the microprocessor performs a light reflectance value assessment and allows the display of the light reflectance value (LRV) relative to a pre-set datum on the LCD 1 1 . The appropriate push-button 14 or 15 may then be depressed to store that reflectance assessment; in the alternative the other push-button may be depressed to reject that assessment and cancel the operation.

After at least two LRVs have been stored in memory, corresponding to two different surfaces, the operation may be triggered to display the difference between those LRVs or the LRV contrast difference. For convenience in operation, that display may simply present a PASS or FAIL as compared to a threshold previously loaded into the device, without the device displaying the actual LRVs.

Further functionality of the device may permit the averaging of a number of assessments of the LRV of a single multi-coloured or textured surface, at points distributed over that surface. For example, natural wood or other textured surfaces may not have a uniform reflectance over the entire area of the surface, so that a number of LRV assessments must be taken to obtain an average LRV. That averaged number may then be compared with a similarly averaged number for another surface proximate the first surface, or a single measurement on a plain surface.

Figure 2 shows a docking station for the device of Figure 1 . This comprises a base 25 defining a socket 26 for receiving the end of the body 10 of the device, opposed to opening 12, the socket having a pair of contacts 27 to mate with contacts 24 on the body 10. A power supply unit 28 is disposed within the docking station and is supplied with mains power by cable 29, for recharging the battery disposed within chamber 23 of the body 10. An alternative form of the device may include a USB port allowing the uploading of data to a PC, a laptop or hand-held computer and for such a case recharging of the battery may be performed through the USB port, so obviating the need for a docking station.

Figures 3, 4 and 5 show a second embodiment having essentially the same functionality as has been described above in relation to the first embodiment. The second embodiment is configured somewhat differently and is incorporated within an ergonomically designed case which is easier to hold and use. The body 30 is rounded and has a projecting nose 31 within which is provided a colour sensor corresponding to sensor 17 of the first embodiment. The body has an LCD display 32 and operating buttons 33. This embodiment is intended to convey information numerically or by displaying alpha-numeric codes rather than specific words such as "PASS" or "FAIL". In other respects, the second embodiment corresponds to the first embodiment and specifically so far as its manner of use is concerned.

The embodiments of this invention as described above are relatively simple forms of the device. More complex versions thereof may be produced, which still fall within the scope of the appended claims and are in accordance with this invention as defined hereinbefore.

Claims

1 . A portable hand-held device for assessing a difference (contrast) in light reflectance values (the Y values) of two surfaces, which device comprises:

- a manually-grippable body;

- processing means contained within the body and to which the sensor output is supplied, the processing means being arranged to convert said sensor output into an appropriate colour space determination and then to extract from the colour space determination the light reflectance values (Y) of the illuminated surface;

2. A device as claimed in claim 1 , wherein the body is configured to be sufficiently small for holding in one hand.

3. A device as claimed in claim 1 or claim 2, wherein the light source comprises one of a light-emitting diode, an incandescent lamp, a fluorescent lamp or a gas discharge lamp.

4. A device as claimed in any of the preceding claims, wherein the body supports more than one light source.

5. A device as claimed in claim 4, wherein the spectra emitted by the multiple sources differ and are used in sequence to perform a single assessment from the output of the receptor.

6. A device as claimed in any of the preceding claims, wherein the receptor of the colour sensor comprises at least one photodiode.

7. A device as claimed in claim 6, wherein there is a plurality of photodiodes associated with one or more dye-based RGB or CIEXYZ filters.

8. A device as claimed in claim 6 or claim 7, wherein the or each photodiode is associated with one or more transimpedance amplifiers.

9. A device as claimed in any of the preceding claims, wherein the processing means is arranged to convert the sensor output into one of CIEL^*a^*b^*, CIEXYZ, CIExyY, RGB, CMY, CIELUV, YUV, YIQ, YCbCr, II 1213, LSLM, UVW, HSI, HIS polar, HSV, HSV polar, LHC and LHS colour space.

10. A device as claimed in any of the preceding claims, wherein the processing means includes comparison means to determine the difference between two light reflectance values and compare that difference with one or more pre-set criteria.

1 1 . A device as claimed in claim 10, wherein the pre-set criteria includes an acceptable threshold value whereby the comparison signal is indicative of a preset acceptable or unacceptable light reflectance value difference.

12. A device as claimed in any of the preceding claims, wherein the processing means is arranged to permit the storing in the memory means of a plurality of extracted light reflectance values for a selected surface and then to average those values for that surface, for supply to the output means.

13. A device as claimed in any of the preceding claims, wherein the body supports at least two manual controls to allow the storage of an extracted Y value and the comparison of stored Y values to obtain said comparison signal.

14. A device as claimed in any of the preceding claims, wherein the output means includes one or more of a visual display and an audible sounder.

15. A device as claimed in claim 14, wherein the output means comprises one or more of a LCD display, a LED display, a coloured indicator LED or lamp, an OLED display, sound samples, and synthesised or pre-recorded speech.

16. A device as claimed in claim 14 or claim 15, wherein the comparison signal comprises a Y-value and a light reflectance value percentage, and the output device is arranged to allow the visual display of the light value contrast difference between two surfaces.

17. A device as claimed in any of the preceding claims, wherein the output means includes data transfer means arrange to permit the transfer of data from the device to an external electronic device.

18. A device as claimed in claim 17, wherein the data transfer means comprises one of a USB port, a RS232 port, a Bluetooth or other radio frequency wireless transmitter, and an optical or infra-red communication link.

19. Apparatus as claimed in any of the preceding claims, wherein the body includes a chamber having an opening for placement on a surface thereby to exclude external ambient light from the chamber, the colour sensor being mounted in the chamber.

20. A device as claimed in claim 19, wherein the wall of the chamber defining the opening is compliant whereby the opening may conform to the profile of a surface on to which the device is placed.

21 . A device as claimed in claim 19 or claim 20, wherein the placement of the opening on a surface activates the device to perform a Y-value light reflectance value determination.

22. A device as claimed in any of the preceding claims, wherein the processing means is arranged to permit the determination of the Y-value light reflectance value of a single surface relevant to a datum.

23. A device as claimed in any of the preceding claims, wherein the body includes a power source comprising one of a mains operated power supply unit, a rechargeable battery or a single use battery.

24. A portable hand-held device for assessing a difference (contrast) in light reflectance values (the Y values) of two surfaces and substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.