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Clari-Fi

Clari-Fi uses blurring to simulate the challenges of viewing small details on packs and display screens

 

Introduction to assessing printed materials and packs

Clari-Fi can be used to help evaluate the visual clarity (i.e. perceptibility) of digital artwork for flat printed materials and packaging.

This webpage describes the benefits of using Clari-Fi and presents a worked example, firstly for a viewing distance that corresponds to scanning a supermarket shelf, and then for a handheld viewing distance. Finally, further details are provided on who should perform the assessments, how to perform the assessments, and a summary of the population perspective.

On this page:

Checking the visual clarity of printed materials & packs is only available in the Photoshop version of Clari-Fi.

Why use Clari-Fi to assess printed materials

Clari-Fi speeds up the process of designing printed materials that have excellent visual clarity (i.e. perceptibility), because it enables quick and iterative evaluation of the critical details within the artwork, while it's being developed in Photoshop. It uses blurring to simulate the challenges of perceiving the critical details when the artwork is printed at its intended size and viewed at its intended distance.

Clari-Fi is recommended as a quick and approximate check that is intended to be used iteratively at the earliest stages of the development process, and which can eliminate designs that are not worth testing with real users.

The levels of blurring that Clari-Fi uses are calibrated to population data, so provide a rational basis for target setting within design. The check levels are particularly suitable for specifying the level of visual clarity that a design agency's output is expected to pass.

If the printed materials already physically exist, then we recommend that they are assessed using the Cambridge Simulation Glasses because these take better account of the lighting, surface finish and contrast differences between foreground and background colours. The different levels of blurring used within Clari-Fi have been set so that they directly correspond with the degree of impairment simulated by 1, 2 and 3 pairs of these simulation glasses. This is described in more detail within the panels titled Clari-Fi Levels for things viewed at a distance and Clari-Fi Levels for things that are handheld (which are further down this page).

Important notes on checking visual clarity

1. Visual details should be checked with both Clari-Fi AND a contrast checker

  • Passing Clari-Fi means that visual details are presented at a big enough size, but visual details also need to be checked to ensure there is sufficient contrast between the foreground and background colours.
  • We recommend using the Accessible Perceptual Contrast Algorithm (APCA) to check that the Lightness contrast (Lc) is greater than 60 (ideally), or greater than 45 (as an absolute minimum).
  • Some people also have particular sensitivities to extremely high contrasts, which can cause headaches. The APCA Lightness contrast (Lc) should therefore be less than 90.
  • An APCA contrast checker is bundled together with the PowerPoint and Photoshop versions of Clari-Fi (available from the Assessment tools page), and is also freely available at contrast.tools.
  • The APCA Lightness contrast is recommended instead of the contrast ratio that appears in the Web Content Accessibility Guidelines (2.2), because the latter overestimates the contrast of black text on coloured backgrounds, and underestimates the contrast for white text on coloured backgrounds. These different methods for calculating contrast are discussed further in the article titled Does the contrast ratio actually predict the legibility of text?.

2. Visual details should also be checked with a colour vision deficiency simulator

  • Some people may have difficulty perceiving graphical details for reasons other than visual acuity. In particular, colour vision deficiency (often called colour-blindness) affects approximately 8% of men and 0.5% of women. This typically makes red details on black backgrounds (and various other colour combinations) extremely difficult to perceive.
  • We recommend using a freely available colour vision deficiency simulator to check the colour combinations within your artwork, for example:

3. Clari-Fi should complement, not replace user involvement

  • Clari-Fi is a form of expert appraisal that focuses on ensuring details are presented at a big enough size, but real users may have many other issues with perceiving visual details.
  • These include difficulties with determining where to look to find the information, and difficulties with understanding the meaning of the information.
  • Clari-Fi is a great preliminary check that can reject designs that are not worth testing with real users, but passing Clari-Fi does not replace the need to validate with real users.

Worked example

A worked example for packaging will now be presented, based on the artwork shown opposite, which corresponds to a pack that is 12 cm wide. The artwork is first assessed at a viewing distance of 1m (approx. 3 feet), which is fairly typical for scanning a supermarket aisle. At this distance, the following messages are assessed:

  • Recognising the brand: ‘Dove’;
  • Reading the variant name: ‘beauty cream bar’;
  • Reading the benefit claim: ‘1/4 moisturising cream’ (in the bottom gold bar).

The same artwork is then assessed again, assuming the shopper has approached the pack and picked it up to check some of the specific details. The following messages are assessed at a handheld distance:

  • Reading the benefit claim: ‘1/4 moisturising cream’ (in the bottom gold bar);
  • Reading the numerals in the top right that communicate the pack size: '4x90g'.

Clari-Fi levels for things viewed at a distance

Clari-Fi works by processing an image to apply blurring at a few different levels of severity. These levels have the following names, and apply the following degrees of blurring:

  • The 1% Level: Applies a degree of blurring that simulates mild visual impairment1. This is approximately equivalent to someone with good distance vision wearing 3 pairs of Cambridge Simulation Glasses.
  • The 3% Level: Applies a degree of blurring that simulates someone who is not visually impaired1, but is at the limit of the range considered to be normal vision. This is approximately equivalent to someone with good distance vision wearing 2 pairs of Cambridge Simulation Glasses.
  • The 30% Level: Applies a degree of blurring that simulates a level of vision ability where roughly one third of the population have better vision, and roughly two thirds have worse vision. This is approximately equivalent to someone with good distance vision wearing 1 pair of Cambridge Simulation Glasses.

The degree of blurring associated with The 1% Level has been calculated so that:

If the visual details are only just perceptible at The 1% Level, then about 1% of people cannot perceive these details2, at the specified viewing distance.

See the Calculation assumptions for information on how these percentages are calculated. The naming of the other levels follows a similar convention.

The 1% Level applies the most severe degree of blurring, so visual details need to be quite large in order to pass this level. If the visual details pass this level, then there will be very few people who cannot see them.

Conversely, The 30% Level applies much less blurring, so the visual details don’t need to be as big to pass this level.

The images shown opposite show the various different levels for the worked example of the Dove bar packaging, for a viewing distance of 1m.

Assessments should be performed by first checking visual details against the most severe level of blurring (The 1% Level), and then working through to the least severe blurring (The 30% Level). Following this process for the blurred images shown opposite gives the following conclusions:

  • The brand ‘Dove’ is bigger than the bare minimum needed to pass The 1% Level, so less than 1% of people cannot perceive the brand2 (at the viewing distance of 1m).
  • The variant name ‘beauty cream bar’ is bigger than the bare minimum needed to pass The 3% Level, but not big enough to pass The 1% Level, so between 1 and 3% of people cannot perceive the variant name2 (at the viewing distance of 1m).
  • The benefit claim ‘1/4 moisturising cream’ is not big enough to pass The 30% Level, so more than 30% of people cannot perceive this benefit claim2 (at the viewing distance of 1m).

Footnotes

  1. Mild visual impairment is defined in the WHO World report on vision as 20 / 50 to 20 / 60 vision. The 1% Level simulates 20 / 60 vision, which means the person can ‘only just’ perceive test chart letters that are 20 feet away, where the strokes that make up the letters subtend an angle of 3 arc minutes (0.05 degrees) on the retina.
    The 3% Level simulates 20 / 40 vision, which means the person can ‘only just’ perceive test chart letters that are 20 feet away, where the strokes that make up the letters subtend an angle of 2 arc minutes (0.033 degrees) on the retina. In real world terms, 20 / 40 is about the borderline for being able to drive, but it's not severe enough to be classified as visually impaired.
  2. This refers to the percentage of people who cannot perceive the text and icons, because they are too small for them to see, while wearing any glasses or contact lenses that they usually wear for the majority of the day. See the Calculation assumptions panel for further details.

Clari-Fi levels for things that are handheld

Some people have good near vision ability but poor distance vision ability, and some people have good distance vision ability but poor near vision ability. In order to correctly take account of this, the names, population percentages and the degree of applied blurring that is applied for ‘things that are handheld’ are different to those used for ‘things viewed at a distance’.

The levels for ‘things that are handheld’ have the following names, and apply the following degrees of blurring:

  • The 1% Level: Applies a degree of blurring that simulates someone who is roughly in the middle of the range considered as moderate visual impairment1.
  • The 4% Level: Applies a degree of blurring that simulates someone who is at the least impaired end of the range considered as moderate visual impairment1. This is approximately equivalent to someone with good near vision wearing 3 pairs of Cambridge Simulation Glasses.
  • The 20% Level: Applies a degree of blurring that simulates someone who is not visually impaired1, but is at the limit of the range considered as normal vision. This is approximately equivalent to someone with good near vision wearing 2 pairs of Cambridge Simulation Glasses.
  • The 50% Level: Applies a degree of blurring that simulates a level of vision ability where roughly half the population have better vision, and roughly half have worse vision. This is approximately equivalent to someone with good near vision wearing 1 pair of Cambridge Simulation Glasses.

The degree of blurring associated with The 1% Level for ‘things that are handheld’ has been calculated so that:

If the visual details are only just perceptible at The 1% Level, then about 1% of people cannot perceive these details, at a handheld viewing distance.

See the Calculation assumptions for information on how these percentages are calculated. The naming of the other levels follows a similar convention.

The 1% Level applies the most severe degree of blurring, so visual details need to be quite large in order to pass this level. If the visual details pass this level, then there will be very few people who cannot see them.

Conversely, The 50% Level applies much less blurring, so the visual details don’t need to be as big to pass this level.

The images shown opposite show the various different levels for the worked example of the Dove bar packaging, for a handheld viewing distance.

Assessments should be performed by first checking visual details against the most severe level of blurring (The 1% Level), and then working through to the least severe blurring (The 50% Level). Following this process for the blurred images shown opposite gives the following conclusions:

  • The size description '4x90g' is bigger than the bare minimum needed to pass The 20% Level, but not big enough to pass The 4% Level, so between 4% and 20% of people cannot perceive the size description (at a handheld viewing distance).
  • The benefit claim '1/4 MOISTURISING CREAM’ is bigger than the bare minimum needed to pass The 50% Level, but not big enough to pass The 20% Level, so between 20% and 50% of people cannot perceive this benefit claim (at a handheld viewing distance).

Footnotes

  1. Moderate visual impairment is defined in the WHO World report on vision as 20 / 80 to 20 / 200 vision, and 'Not visually impaired’ is defined as 20 / 40 vision (or better).
    The 1% Level is approximately equivalent to 20 / 140 vision, which means the person can ‘only just’ perceive test chart letters when the strokes within them subtend an angle of 7 arc minutes (0.117 degrees) on the retina3.
    The 4% Level is approximately equivalent to 20 / 90 vision, which means the person can ‘only just’ perceive test chart letters when the strokes within them subtend an angle of 4.5 arc minutes (0.075 degrees) on the retina3.
    The 20% Level is approximately equivalent to 20 / 40 vision, which means the person can ‘only just’ perceive test chart letters when the strokes within them subtend an angle of 2 arc minutes (0.033 degrees) on the retina3. In real world terms, 20 / 40 vision is about the borderline for being able to drive, but it's not severe enough to be classified as visually impaired.
  2. This refers to the percentage of people who cannot perceive the text and icons, because they are too small for them to see, while wearing any glasses or contact lenses that they usually wear for the majority of the day. See the Calculation assumptions panel for further details.
  3. Visions tests for 20 / X vision are conducted at a viewing distance of 20 feet. For apps and websites, near vision equivalents are needed, and the best available approximation is to assume the same threshold visual angles, and a viewing distance of 40cm (1.3 feet).

Setting targets for inclusive communications

Inclusive graphic designs should aim to pass The 1% Level, if possible. If there are unavoidable constraints that mean it’s not possible to pass The 1% Level, then aim to pass the smallest percentage level (i.e. most severe blurring) that can be achieved, within these constraints.

In general, near vision is much more affected by age than distance vision, so near vision exclusion levels tend to be much higher. For many things that are handheld, The 4% Level may be the best that’s pragmatically achievable.

Who should perform Clari-Fi assessments?

Using Clari-Fi to assess printed materials is more objective than an assessor looking at the digital artwork directly, and deciding if they think the critical messages are communicated clearly enough.

However, some degree of subjectivity remains in the process, because the assessor's familiarity with the graphic design of the artwork (and its wider context) can influence the details that they need to perceive in order to understand the critical messages conveyed by the artwork.

For example, if Clari-Fi was being used to assess a map for a building, then the map shouldn't be assessed by the person that designed it, and it shouldn't be assessed by someone who already knows their way around the building. Instead, it should be assessed by someone who hasn't seen the map before, and whose knowledge of the building is similar to that of the intended users of the map.

Nevertheless, the person who designed the map will still gain considerable insight from performing the Clari-Fi assessment themselves, as long as they:

  • are consciously aware of the advantage that their prior experience gives them in perceiving the details that they are assessing;
  • do their best to mitigate this issue when performing the assessments.

Having the designer of the visual materials perform the Clari-Fi assessment allows for very fast iteration cycles of improvement and testing. However, it's important that these Clari-Fi assessments are validated by someone else who hasn't worked on the project, and ultimately validated with real users, as described further in the panel titled Important notes.

The assessor's eyesight ability doesn't usually matter, as long as their vision is good enough to drive, and they don't have any specific issues with near vision (wearing glasses or contact lenses if needed).

How to perform a Clari-Fi assessment

To assess printed materials at The 1% Level:

  1. Recruit an appropriate assessor, as described in the panel titled Who should perform Clari-Fi assessments?
  2. Set up a laptop or monitor screen for the assessment, so that The 1% Level version of the image is visible on the screen (at the largest possible size), and nothing else.
  3. Show this image to the assessor. The exact size at which the image is presented, how far away the monitor is and whether the assessor has perfect eyesight don’t usually matter. Within reasonable variations of these parameters, it’s the applied blurring that limits the graphical details that can be perceived.
  4. Ask the assessor to look at this image, and see if they can successfully perceive the critical messages that the image intends to communicate. These messages pass The 1% Level if the assessor can determine them from the blurred version of the image.

If any of the messages fail at The 1% Level, this procedure can be repeated to test at the other levels that apply successively less blurring.

It is fine to repeat the test procedure multiple times at successively less blurring, but it is never suitable to repeat the test at a level that applies more severe blurring than the previous test, because the details that you have already seen within the mildly blurred version of the image will subconsciously assist your perception of the more severely blurred version.

Taking a population perspective

Firstly, follow the assessment procedure, which was described previously in the panel titled How to perform a Clari-Fi assessment. A summarised description of this procedure is:

  1. Recruit an appropriate assessor, as described in the panel titled Who should perform Clari-Fi assessments?
  2. Ask them to look at The 1% Level blurred version of the image, and see if they can perceive the critical messages that the image intends to communicate.
  3. If any of the messages fail at The 1% Level, then test again at the other levels that apply successively less blurring.

Having completed this procedure, consult the statements below, which relate the outcome of this assessment to population data, firstly for ‘things viewed at a distance’, and then for ‘things that are handheld’.

Population perspective for ‘things viewed at a distance’

  • If the visual details are bigger than the bare minimum needed to pass The 1% Level
    then less than 1% of people cannot perceive these details1.
  • If the visual details are bigger than the bare minimum needed to pass The 3% Level,
    but not big enough to pass The 1% Level,
    then between 1 and 3% of people cannot perceive these details1.
  • If the visual details are bigger than the bare minimum needed to pass The 30% Level,
    but not big enough to pass The 3% Level,
    then between 3 and 30% of people cannot perceive these details1.
  • If the visual details are not big enough to pass The 30% Level,
    then more than 30% of people cannot perceive these details1.

Population perspective for ‘things that are handheld’

  • If the visual details are bigger than the bare minimum needed to pass The 1% Level
    then less than 1% of people cannot perceive these details1.
  • If the visual details are bigger than the bare minimum needed to pass The 4% Level,
    but not big enough to pass The 1% Level,
    then between 1 and 4% of people cannot perceive these details1.
  • If the visual details are bigger than the bare minimum needed to pass The 20% Level,
    but not big enough to pass The 4% Level,
    then between 4 and 20% of people cannot perceive these details1.
  • If the visual details are bigger than the bare minimum needed to pass The 50% Level,
    but not big enough to pass The 20% Level,
    then between 20 and 50% of people cannot perceive these details1.
  • If the visual details are not big enough to pass The 50% Level,
    then more than 50% of people cannot perceive these details1.

Footnotes

  1. This refers to the percentage of people who cannot perceive the details, because they are too small for them to see at the specified viewing distance, while wearing any glasses or contact lenses that they usually wear for the majority of the day. See the Calculation assumptions panel for further details.

Calculation assumptions

Population percentages refer to people who cannot perceive particular visual details, because they are too small for them to see at the specified viewing distance. Importantly, there are many other reasons that might cause people to have difficulty perceiving these details. Clari-Fi assessments should be accompanied by checking contrast, simulating colour vision deficiency, and testing with users, as described in the Important notes section (earlier on this page).

All population figures presented on this page are estimated based on a household based UK survey1 with 362 participants conducted in 2010, which tested people’s near vision and distance vision. To find out more about the survey, see the page titled Relating the Clari-Fi levels to population data.

The tests intended to measure people’s ‘real-world’ vision ability (i.e. the level of near vision ability that they have for the majority of the day). So, if participants were wearing glasses or contact lenses before the test, then they kept them on. If they weren’t wearing any glasses or contact lenses before the test, then the test was conducted without glasses or contact lenses.

On this basis, all population figures on this page refer to the percentage of people who cannot perceive particular details ‘natively’, without any assistive strategies2 or assistive devices3. This matches the aim of inclusive solutions, which shouldn’t require people to use assistive strategies or devices.

Footnotes

  1. Towards better design, 2010. [data collection]. UK Data Service, SN: 6997. Available at: dx.doi.org/10.5255/UKDA-SN-6997-1
  2. One common assistive strategy is to use a mobile phone, either as a portable magnifier, or by taking a photo and then zooming in. For people who are heavily shortsighted viewing things that are handheld, another possible assistive strategy is to drop the glasses down low on the nose, look over the top of them, and hold the stimulus very close to the nose.
  3. Common assistive devices include handheld magnifiers and reading glasses.

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