Wednesday 25 March 2015

Human Bias - The Dress Viral Phenomenon

What started out as a viral phenomenon on social media in recent weeks quickly spread into the mainstream and scientific discourse.  Everyone seemed to be talking about the dress.  I first heard about it when a discussion broke out in the office where I work, then every office across the building.  Then it even made the evening news.  Every discussion was divided between those who saw a blue and black dress and those who were equally convinced the dress was white and gold.

The scientific explanation appears to centre around ones individual perception of the lighting in the image.  Some are happy to accept that the dress is reasonably well lit and that it's blue colour in particular is correct.  Others are somehow compensating for the bright sunlight and are discounting the blue colour.  What was most interesting of all was to note the reaction of people who discovered their analysis was wrong.  The dress is indeed blue and black, as confirmed by the designer.  But it seems that it is very hard to teach the brain based on this new information.  Human bias is a powerful thing as we know.  Once the brain locks on to an idea it can be difficult to change.

Sampling of the blue fabric from the unaltered original image confirms that it is clearly blue and this is how we should perceive it from a screen.  However the stats suggest that as few as one third of people actually perceive it this way.  The black material of the dress is not so clear.  That material is reflecting ambient light and doesn't look particularly dark in the image.  Black as we know is not a colour at all but rather a luminance level.  The image as a whole is underexposed and lightened so the darker tones are not well expressed.  I.e. blacks are not entirely black in the image.  In fact in this image this material measures as a dark golden or brown colour.  It is possibly this element is part of the trick.  But some of the scientific argument also points to the bright, back light as being relevant, and possibly the real trigger.  There is obviously much more to our perception of colour and light intensity than we might first suspect.  

In the image above I have used the levels tool in Adobe Elements to adjust the white point (lower left inset) and black point (lower right inset).  It would seem that a white point adjustment alone is enough to closely match the white and gold dress phenomenon, suggesting that it is primarily a lighting perception phenomenon rather than a colour phenomenon.  That said, those who observe a white dress may be using a touch of white balance correction to remove any remaining pale blue from the image as well.

It is not unusual of course for people to disagree over optical illusions.  This image is well known to most as it may be described as depicting a young woman with her neck exposed, looking away or an older woman, wrapped up, with her face in profile.  

However, with this illusion it is easy for people to appreciate both options.  With the dress this doesn't appear to be the case.

The checker shadow illusion (below) may be similar to this phenomenon but unlike that illusion which seems to fool pretty much everyone, the dress seems to divide people in the ratio of about 2:3.

The video below is some of the clearest online analysis.  14 seconds into this video a female subject appears to experience a change in her perception from the more accurate blue and black colouration to the brighter, more washed out, false white and gold colouration.  This would suggest that there is a certain, elusive trigger for it which we should presumably be able to access, as opposed to there being an inherent difference between the visual perception of two cohorts of the population   I am sure someone will figure that out eventually and feed it back to us over social media.  For now it remains an interesting party trick and source of debate.

If the back lighting is the trigger for this anomaly, this might suggest we should watch out for this surfacing in the analysis of underexposed, back lit bird images.  I am sure there will be plenty of debate about this for years to come.  As for this blog, well this lesson has reminded me that readers of this blog may well perceive the image content here in different ways.  I believe in presenting not only what I can see in the images but what can be verified using the tools discussed.  In a birders colour pallet I came up with a method to measure and describe colour without even requiring colour vision.  This is one way in which I think we can get around the subjectivity of colour analysis.

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