GB2462263A

GB2462263A - Sign with high spatial frequency image.

Info

Publication number: GB2462263A
Application number: GB0813835A
Authority: GB
Inventors: Stuart Greenshields
Original assignee: TRL Ltd
Current assignee: TRL Ltd
Priority date: 2008-07-29
Filing date: 2008-07-29
Publication date: 2010-02-03
Also published as: GB0813835D0

Abstract

A first portion 110 of sign 100 is provided with a high spatial frequency image 120. The first portion is formed, e.g. of a semi-transparent diffusing screen, so that it transmits light from a background scene, to form a low spatial frequency image. A second portion 130 which is transparent may be provided extending beyond the first portion. The first portion may be retroreflective. When viewed from beyond a threshold distance (D), only the low spatial frequency image of the background is visible. When viewed from less than the threshold distance (D), the high spatial frequency image 120 is visible, contrasted against the low spatial frequency image. The sign may reduce visual intrusion. The invention also comprises a traffic control system or an information system for pedestrians or people in a building, and a method of manufacturing a sign.

Description

Field of the Invention

The present invention relates to the field of signage.

The invention may be applied, for example, to road signs, or signs for pedestrians.

Background of the Invention

Signs convey information to people. Signs may be used in a wide variety of locations, both indoors and outdoors.

Major uses of signs include roads, workplaces, building sites and pavements.

The factors determining the legibility of signs include: (i) size of writing or image; (ii) whether or not the sign is illuminated; (iii) visual acuity of the reader; (iv) location of the sign; (v) contrast with the surroundings.

In many conventional applications, a sign is manufactured to be as prominent as possible. In order to achieve this, the size, location and/or illumination of the sign are usually chosen to maximize its visual impact and legibility.

Known problems with signs include visual intrusion. At least two aspects of visual intrusion can be identified: (i) Visual clutter' . Visual clutter occurs when the number and/or size of signs detracts from the visual appeal of a location, for example an attractive landscape.

I

(ii) Information overload' . The number of signs and/ or the total amount of information on the signs may lead to too much information being presented to an observer. If the observer then makes mistakes, misses vital information, or becomes confused, there may be adverse implications for safety.

A prior art arrangement involves first and second images arranged on the same medium. The first image is of relatively low spatial frequency, and the second image is of relatively high spatial frequency. With this arrangement, the first image is legible from further away than the second image. Such an arrangement is often termed a hybrid image'

For examples of these prior art arrangements, see:

(i) Huang, G. T., Step away from this page', New Scientist, 31 March 2007, pp 35-37.

(ii) Oliva, A. Torralba, A., and Schyns, P.G., Hybrid Images' http://cvci.rnit.edu/hvbrid/Taik Hybrid S.igqraphO6pdf (iii) Schieber, F. Using the "Blur Tolerance" Technique to Predict and Optimize the Legibility Distance of Symbol Highway Signs' http: //www usd. edu/schieber/pdf/bpredict pdf (iv) Oliva, A., Torralba, A. and Schyns, P., Hybrid Images' ACM Transactions on Graphics, 2006, pp. 527-532.

Reference (i) above highlights how two images of different spatial frequency can be placed on the same medium, and are each separately viewable from different distances.

The mechanism underlying this effect concerns each image's spatial frequency, which is the number of

contrast changes per degree of field of view. Only

certain frequencies can be viewed by the eye, and registered by the brain. The degree of field of view of an image changes with the distance of the eye from it, which leads to the changes in viewability outlined above.

The Gestalt effect' is also known in the prior art. This effect involves the brain forming whole images from a collection of light and lines. From far away, the brain interprets a low spatial frequency image as being more defined than it is in a gestalt' way. A high frequency image is not interpretable from this distance. From a closer distance, the high frequency image is viewable against the background of the relatively low frequency image, in part because of the contrast between them.

Statement of Invention

In accordance with a first aspect of the invention, there is provided a sign as claimed in claim 1.

In accordance with a second aspect of the invention, there is provided a traffic control system in accordance with claim 17.

In accordance with a third aspect of the invention, there is provided an information system for pedestrians in accordance with claim 18.

In accordance with a fourth aspect of the invention, there is provided a method of manufacturing a sign in accordance with claim 19.

The appended dependent claims provide details of further preferred features of embodiments of the invention.

This invention allows for a reduction in the long-range visual intrusion of signs. This is particularly important where an observer might be subject to information overload, or in areas of scenic beauty. The invention may be used for signs for drivers, indoor and outdoor pedestrians, cyclists, advertising or variable message signs, but is not limited to these applications.

The invention also overcomes a drawback of prior art images, which is that the images on the medium are fixed, and cannot alter to suit the surrounding environment.

This is the case, for example, with the images prThted on a single medium shown in the Huang prior art reference (i) discussed above. With the invention, the low spatial

frequency image is actually the blurred background

scenery behind the signboard, and is dynamic. The

background image appears on the signboard, but is

actually light transmitted through the signboard.

Brief Description of the Drawings

Figure 1 shows a sign in accordance with the present invention.

Figure 2 shows a sign in accordance with the invention, viewed from beyond a threshold distance.

Figure 3 shows a sign in accordance with the invention, viewed from less than a threshold distance.

Figure 4 shows two signs, and the location of an observer.

Figure 5 shows a traffic control system.

Description of Preferred Embodiments

With the arrangements known from the prior art cited above, any images on a medium are fixed. The images therefore do not alter to suit the surrounding environment.

With the invention, the low spatial frequency image can be provided by diffuse light from the surrounding background. One mechanism for achieving this is by using a semi-transparent diffusing screen.

The inventors have also addressed the problems of signs that cause visual intrusion, which may contribute to visual clutter and/or information overload. The visual intrusion arises in situations where signs are visible beyond a distance that is needed for reading the sign.

Such visual intrusion may be a particular problem for highway signs. It may also occur, for example, in buildings and pedestrian streets.

The invention may involve the signboard portion of a sign providing the diffuse light from the surrounding background. Wording and images of a relatively high spatial frequency would be placed onto the signboard, which may comprise a semi-transparent diffusing screen.

With this arrangement, the signboard and wording would not be registered by the brain at a long distance.

However, the wording or images placed on the signboard would be registered when closer.

This arrangement would substantially reduce or eliminate the visual intrusion of signs when viewed from beyond the distance that is needed for reading the sign.

The invention can be understood using the example of a visual sign used in transportation. In this example, the sign might welcome drivers to a village in a rural area.

The sign is not of importance for safety, but is located in an area that is sensitive to visual clutter.

The outline of the graphic of the sign would be laid upon a signboard. The width of the outline of the worthng can be optimised to a high spatial frequency that can be viewed from a predetermined distance. That distance might, for example, be in the region of lOOm.

The signboard itself may be semi-transparent over only part of its surface. In this case, the semi-transparent part lies behind and around the area where the graphic, e.g. wording, is placed. The semi-transparent part blurs images that are seen through it. However, the signboard might be completely transparent in other areas, further from the area where the graphic is placed.

From a distance in excess of a predetermined threshold distance, the sign cannot then be perceived by the naked eye, because the light diffused through the signboard is perceived by the brain as part of the general scenery. At the predetermined threshold distance or closer, the graphic on the sign becomes perceptible to the naked eye.

The contrast between the blurred image of the background and the sharpness of the graphic allows the graphic to be seen clearly.

Figure 1 shows a sign 100, in accordance with an embodiment of the invention.

Sign 100 comprises a first portion 110. First portion 110 is adapted to transmit light from a background scene, to form a low spatial frequency image. The background scene consists of objects located behind sign 100.

A high spatial frequency image 120 is located on the first portion 110. As an example of a high spatial frequency image 120, figure 1 shows the words Lay-by' Figure 1 shows sign 100 as it would appear when viewed from a distance that is less than a threshold viewing distance D. At a viewing distance less than threshold viewing distance D, the high spatial frequency image 120 is clearly visible. Threshold viewing distance D s not shown on figure 1, but is explained further in connection with figure 4 below.

The invention therefore provides a hybridised display of a high spatial frequency image 120, and a low spatial frequency background image on first portion 110. Rather than printing the low spatial frequency image to the signboard, this image is actually the blurred background or scenery behind sign 100. The blurred image of the background scene appears on sign 100, but is actually light transmitted through sign 100.

First portion 110 of sign 100 provides a dynamic low spatial frequency image, rather than the fixed images

discussed above in connection with the prior art.

The image is dynamic in at least two ways: (i) As an observer moves to various different viewing points in front of sign 100, the set of objects in the background changes. This is because the background scene for an observer comprises all the objects approximately in line of sight behind first portion 110.

(ii) The objects in the background scene may change, as they move. If there are plants in the background scene, for example, they will move on a windy day. The perceived colour of objects in the background may also change by time of day and season.

The first portion 110 of sign 100 may be made up from a semi-transparent diffusing screen. The effect achieved by such a screen is to cause blurring of the light transmitted through it. This blurring provides a predetermined low spatial frequency of the light transmitted through first portion 110 from the background scene.

Sign 100 may comprise a second portion 130, the second portion 130 being transparent.

Second portion 130 may extend at least from an edge of the first portion 110 to an object on which the sign is mounted. However, embodiments of the invention may alternatively be constructed without second portion 130, in which case first portion 110 is mounted directly on an object.

The purpose of second portion 130 is to support the sign, i.e. to hold up first portion 110. By being transparent, second portion 130 does not contribute to visual intrusion, since it is possible to see through this portion of the sign to whatever is behind. To an observer who is far from the sign, second portion 130 is not readily visible.

Second portion 130 is connected to the object on which the sign is mounted. That object might be, but is not limited to, the ground, a wall, a vehicle, a cable, a string, a window, or a post.

Sign 100 may be permanently affixed, for example by embedding the lower extremity of second portion 130 in a verge beside a road. However, sign 100 may be portable, and/or releasably mountable on an object.

In order to understand the effectiveness of the sign, reference is made to figure 2.

Figure 2 shows the same sign as figure 1, as it would appear when viewed from a distance that is greater than the threshold viewing distance D. In figure 2, the sign 200, first portion 210 and second portion 230 are all visible. However, the high spatial frequency image is not visible.

Figure 3 shows sign 300, with first portion 310, high spatial frequency image 320 and second portion 330.

The outer part of first portion 310 comprises an edge portion 340. The inner boundary of edge portion 340 is shown on figure 3 by border 350.

The surface of first portion 310 within border 350 allows for a constant blurring of light transmitted through it

from the background scene. However, the amount of

blurring reduces progressively from this constant level down to zero across edge portion 340, moving outwards from border 350 to the outer boundary of edge portion 340.

This reduction in blurring is referred to as dithering'.

The effect of this dithering is to reduce the visual effect of the contrast in spatial frequency between light transmitted through the part of first portion 310 within border 350 and light transmitted through second portion 330. This reduction occurs because the contrast in spatial frequency between the edge portion 340 and the second portion 330 is lower than that between light transmitted through the part of first portion 310 within border 350 and light transmitted through second portion 330.

In embodiments of the invention that do not have second portion 330, the effect of this dithering is to reduce the visual effect of the contrast between light transmitted through the part of first portion 310 within border 350 and light that passes outside first portion 310, directly to an observer's eye from the background scene.

Various advantageous features are now described with reference to figure 1, although these also apply to the embodiments of figures 2 and 3.

First portion 110 may comprise minor deflections as part of its shape, whereby the first portion 110 is retroreflective. In addition, the high spatial frequency image 120 may be retroreflective.

First portion 110 may be manufactured using a clear material as the starting point. First portion 110 is then subjected to a treatment including one or more of the group of working, applying substances, and applying processes to the material. The result of this treatment is that first portion 110 blurs the light coming through it, so as to lower the spatial frequency of the light image passing through it. The working, applying substances and/ or applying processes to first portion may also render it retroreflective.

The treatment of first portion 110 may include at least one from the group of: blasting; sanding; applying greases; a chemical process; or providing an adhesive object. The adhesive object may comprise a sticker or some other form of adhesive laminate. The adhesive object may provide first portion 110 with the retroreflective property referred to above.

First portion 110 may therefore be made of the same material as second portion 130. In this case, the manufacturing process could therefore start with a large sheet of clear material. The sheet would be treated in the region of first portion 110, over a sufficiently large area for first portion 110 to completely underlie and surround the area on which high spatial frequency image 120 is to be created.

High spatial frequency image 120 may comprise a pre-determined number of contrast changes per degree of angle of viewing, at a threshold viewing distance (D) . The pre-determined number of contrast changes may be chosen to make the high spatial frequency image 120 illegible beyond the threshold viewing distance (D) . Put more simply, once the desired maximum viewing distance is known, the number of contrast changes needed to ensure illegibility of high spatial frequency image 120 beyond that distance can be set. This and other aspects of the design of the sign may, optionally, be determined by the use of a software design tool.

A number of contrast changes that lies in the range of 4- 8 changes per degree of viewing angle allows an image to be visible to a person with typical visual acuity. So the image cannot be made out clearly if the observer s further away than the point where he perceives 8 contrast changes per degree of viewing angle. If the threshold viewing distance D is to be set at 50 metres, then the image on the sign can be designed such that an observer located 50 metres from the sign sees 8 changes per degree of viewing angle. If the observer moves to a point further than 50 metres from the sign, then the image will no longer be visible.

Considering a high spatial frequency image 120 with a certain range of contrast changes per degree of viewing angle, it is clear that various type-faces or drawing styles may be used. The thickness of the line used in the image, particularly in wording, is a function of the viewing distance required for the wording. The invention is not restricted to the outline' style of letters used in figures 1 and 3. For some desired threshold viewing distances D, with an ideal spatial frequency, the wording could be a solid typeface.

There is some natural variability in visual acuity, between different people. The threshold viewing thstance (D) for a given sign may therefore vary within a small percentage for different individuals with unimpaired vision.

If the number of contrast changes is chosen to be 6 changes per degree of viewing angle, the visibility is optimized. Importantly, at distances above the threshold viewing distance (D), the number of contrast changes lies above the maximum number in the range 4-8 changes per degree of viewing angle, and for this reason the high spatial frequency image is illegible above the threshold viewing distance (D) . The viewing distance at which the predetermined number of contrast changes is 6 would therefore be significantly below the threshold distance, in typical applications of the invention.

The invention therefore offers the possibility of designing a sign that: (i) Has a threshold viewing distance, and is illegible from further away; and (ii) Has a settable optimum viewing distance', at which the sign's legibility is maximized.

If the number of contrast changes is chosen such that the optimum viewing distance is, for example, 100 metres, then the threshold viewing distance might then be around 133 metres. This is because the optimum viewing distance is the point where there are 6 changes per degree of viewing angle, and few individuals can read the sign at a distance where there are more than about 8 changes per degree of viewing angle. So the threshold viewing distance D is likely to be around (8/6) times as great as the optimum viewing distance, in most applications, i.e. 33% greater. Even an observer who could read signs with a range of 4-10 changes per degree of viewing angle would find that the threshold viewing distance D lies (10/6) times as far away as the optimum viewing distance, or 66% further away.

The example of figure 1 shows the simple phrase Lay-by' as the high spatial frequency image 120. However, high spatial frequency image 120 may comprise at least one, but is not limited to, the group of: wording; pictures; symbols; a direction indicator; a border; a number; a projected image; a moving image.

High spatial frequency image 120 may be created by at least one from the group of: machining, stamping, printing, chemical process, providing an adhesive object, light projection. However, this list is not limiting, and high spatial frequency image 120 may be created in other ways.

As mentioned above, the spatial frequency of the wording may be set for the desired maximum visual sighting distance, i.e. threshold viewing distance D. However, perception is increased with contrast. So the invention may be further enhanced by optimising the colour of high spatial frequency image 120 to provide contrast with a

likely prevailing background colour.

This may involve selecting a colour, or be achieved by using a polarizing filter for the high spatial frequency image 120 that will provide a high degree of contrast

with colours of the likely prevailing background.

Second portion 130 of sign 100 is made of a transparent material that allows the transmission of light through it. Clear glass or plastic are suitable materials. For road traffic applications, plastic may be more suitable, due to the risk of impacts. For a sign mounted within a building above head height, for example, the aesthetic appeal of glass may however prevail.

Sign 100 could incorporate mouldings or shaping to increase its strength, in order to withstand external forces such as wind. The signboard could also be continuous to the ground, i.e. second portion 130 may extend from the lower edge of first portion 110 all the way down to the ground. The signboard material could be a material which shatters safely when impacted by a large moving object, such as a vehicle.

The advantage of transparent second portion 130 is that the first portion 110 does not appear to be directly attached to anything. At distances beyond threshold distance D, sign 100 may therefore be almost entirely invisible to a casual observer.

The quality of the sign depends on a number of issues, including: (i) The accuracy of the blurring of first portion 110 to produce the correct spatial frequency of the light of the background image transmitted through the signboarcl; and (ii) Choice of the correct spatial frequency of the image and/or wording making up the high spatial frequency image 120.

The sign can be optimised by correct dithering of the blurring of edge portion 340, enabling a reduction of the contrast between the blurred area and the non-blurred areas.

Advantageously, in some applications measures may also be taken to limit the reflection from sign 100. This may be important in outdoor uses of the sign, such as beside a highway, where low sun angles might lead to reflections and hence glare. A non-reflection surface, treated in such a way that it reduces reflection, may therefore be provided. This might provide, for example, a satin' surface. Such a surface would reduce the glare from sunlight and from the headlights of vehicles. If second portion 130, 230 were large, then a non-reflection surface would be of particular advantage when applied to that portion.

Figure 4 shows two signs, and the location of an observer. These signs might be indoors or outdoors.

Sign 410 in figure 4 is closer to observer 420 than the threshold distance D. The words Lay-by' are therefore visible to observer 420. The words Lay-by' stand out in contrast to the low spatial frequency image of the background provided by the first portion of the sign 110, see figure 1.

Sign 430 in figure 4 is located further from observer 420 than threshold viewing distance D. The image on sign 430 is therefore not visible to observer 420. Sign 430 has been shown as a dotted representation. This is to indicate the location of sign 430 for the purposes of this figure.

Threshold viewing distance D is a parameter that may vary between signs. So the threshold viewing distances for signs 410 and 420 may differ. Figure 4 is simply designed to illustrate a situation where observer 420 is closer to sign 410 than its threshold viewing distance, but further from sign 430 than its threshold viewing distance.

Figure 5 shows a traffic control system 500. A section of road 510 stretches into the distance. Part of a junction at the beginning of the road is shown as dotted line 520.

A stop line' at the end of the road is shown as line 530.

Signs 540, 550, 560 and 570 are located at successively greater distances along the road. These signs are oriented towards a driver traveling in the direction from line 520 to stop line 530.

Signs 540, 550 and 560 are constructed in accordance with the embodiment of the invention as described with reference to figures 1 to 3 above.

The high spatial frequency images on signs 540 and 550 are visible from the start of the road at line 520.

Sign 560 is not visible from the start of the road at line 520. This is because sign 560 is located further from the start of the road than threshold distance D. Sign 570 is a conventional high visibility sign, and bears the word STOP' . Sign 570 is designed to give as much advanced warning as possible to a driver. Sign 570 is therefore visible from the start of the road at line 520.

The combined effect of signs 540, 550, 560 and 570 is to reduce distraction for a driver located at the start of the road 520. Sign 560 is not visible to that driver, allowing the driver to focus earlier on the content of sign 570.

The traffic control system of figure 5 may therefore reduce both visual clutter and information overload. The overall traffic control effect achieved by the arrangement of figure 5 is therefore superior to prior art arrangements that comprise only signs designed to maximize the distance at which the signs are visible.

Sign 570 could also be a conventional' non-high visibility sign, i.e. neither a high visibility sign nor a sign designed in accordance with the principles outlined in connection with figures 1-3 above.

Although the arrangement of figure 5 is an outdoor setting, analogous applications of the invention to indoor scenes are possible. A long hospital corridor, a railway station or an airport terminus are settings where a series of signs of the form shown in figure 5 could be applied to regulate the amount of information visible from one location. In such an information system, signs designed in accordance with the principles outlined in connection with figures 1-3 above would be used together with conventional signs. These conventional signs may include a wide variety of printed, embossed or lit indoor signs.

At an airport, the invention might be applied to signs for passengers on foot or on moving walkways withTh the terminus, or to aircraft moving on an apron or runway.