Camera-based Colour Contrast Evaluation

• This project studies whether or not a digital camera can be used to evaluate colour difference or colour contrast. When characterizing a test object that changes colour over time it is not always possible to do a normal colour measurement with a spectroradiometer. The alternative could be to use film or rapid fire photography to record the changes and extract the colour data from the digital information. This project involves development of a method where spectroradiometric data of a colour chart is compared to digital data taken from photos and film of the same colour chart using Photoshop. In each measurement 22 colours have been evaluated by calculating the colour difference between a direct spectroradiometric measurement of a single colour and data taken from Photoshop of that same colour. The data is compared in the CIELAB colour space using the ?E94 metric which should faithfully represent how the human eye perceives colour difference. Three sets of measurements are made .Two sets where the spectroradiometric data is compared to data from still photos, first with photos directly from the camera and then with RAW-data from the camera. The third measurement compared the spectroradiometric data with data from a frame from a video. The results show that the 22 colours are reproduced with varying degrees of accuracy in photos and video compared to a direct measurement using a spectroradiometer. For the two photo measurements the results span from ?E94 = 0.82 for the best colour reproduction to ?E94 = 17.01 for the worst reproduction. The average deviation was ?E94 = 7.48 and ?E94 = 8.46 respectively where a colour difference of ?E94 =1.0 is considered a just noticeable difference. For video the deviation spans from ?E94 = 4.89 to ?E94 = 18.11 with an average deviation of ?E94 = 11.59. ?E94 has also been used to evaluate how the colour contrast between two different colours differ between the spectroradiometric measurement and data from Photoshop. The results show that for photos the colour contrast deviates quite a bit between the two methods. A deeper evaluation of the video method shows that as long as the contrast between two colours is small the deviation compared to the spectroradiometric measurement will also be small.

Publikations- och innehållstyp

ref (ämneskategori)

rap (ämneskategori)