After a photo of a dress emerged online in February 2015, the world of social media was divided into two groups over the colour of the dress.
One group claimed that the dress was a combination of white and gold, whilst the other believed that the dress colour was in fact a combination of black and blue.
After a great deal of online debate, the actual colour of the dress was confirmed to be the combination of black and blue (Figure 3).
Figure 1. A photo of “The Dress” showing a combination of white and gold
Our Perception of Colour
The controversy over the colour of the dress led to an interesting debate and encouraged the world's media to ask several experts why people had different opinions over the colour of the dress. According to experts, everyone perceives colour differently.
Studies have shown that people interpret images differently when they see them on a computer monitor or television, compared to when view them in print form. The reason for the controversy over the colour of the dress can be easily understood if we examine the “anatomy” of a digital camera, rather than the anatomy of the human eye itself.
The Influence of White Balance
There is no difference whether the photo of “The Dress” was captured using a point-and-shoot, digital SLR (in full auto mode) or cell phone camera. Most digital cameras follow the following process in order to capture an image:
- The camera is turned on
- The camera is focused on the subject
- The shutter button is now pressed
- The camera explores the information in the centre of the scene and changes the lens focus, evaluates the light level, chooses the exposure and changes the colour balance based on the scene content
- The picture is captured and saved
A digital camera captures pictures using an array of Red, Green, and Blue pixels. These three channels are then manipulated by the camera’s technology based on the light source. This process is known as ‘White Balance.’ The accurate reproduction of colours relies on the camera settings or the content of the scene.
The camera view was centred on a dark band of the dress while taking the photo of “The Dress”, as shown by the red rectangle in Figure 2. Using the information detected in this region, the camera decided to use a longer exposure time.
However, the longer exposure time led to over exposure of the image background as the dress was hanging in front of a bright window. As a result, the dress’ black areas appeared much lighter (somewhat gold) than their actual colour.
Figure 2. When the photo of “The Dress” was taken, the camera view was centred on a dark band of the dress.
The camera was then trying to determine the correct colour scheme or White Balance. A typical automatic White Balance algorithm evaluates the information from the image to select a setting but makes a decision largely influenced by the brightest values determined in the Red, Green and Blue channels of each of the camera sensors.
In the centre of this scene, the Blue channel only responded strongly and there was no feedback from the Red or Green channels to the camera sensor. Therefore, the camera increased the Red and Green channel signals in response to what it detected, trying to balance the scene to what the program considered as a ‘real-world’ image.
In this image, if the ‘colour balance’ decision by the camera was based on the information in the red rectangle of Figure 2, the camera had access to only Black and Blue feedback and there it attempted to change the settings. As a result, the blue appeared as white.
Figure 3 shows the photo of “The Dress” in its ‘real-world’ colour or in how it looks in a photo captured under studio lighting with the help of a correctly colour balanced camera. The application of post-processing on the image shown in Figure 2 reduced its overall brightness, making the darker stripes appear black.
Figure 3. The photo of “The Dress” showing how the dress looks in real life
Figure 4 shows the final post-processing result, showing how a colour balance adjustment eliminates the amplification applied to the Red and Green channels of the image by the camera. As a consequence, the light-coloured stripes were restored to Blue. Although the image background is still overexposed, the image shows the actual colour of the dress.
Figure 4. The final post-processing result of “The Dress”
The camera’s response needs to be controlled to the available light source to allow the colour sensor to apply only the required amount of compensation in order to obtain an appropriately balanced result.
Whether taking photos under fluorescent bulbs, Halogen lamps, under a cloudy sky, or in direct sunlight, an appropriate White Balance for the colour temperature of the light needs to be established using the camera’s tools. Failing to do so, will cause all the colours in the image to be biased and misinterpreted by the viewer.
This information has been sourced, reviewed and adapted from materials provided by Lumenera Corporation.
For more information on this source, please visit Lumenera Corporation.