BOLD: Birmingham Object Lighting Database
Technical pages

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This page provides technical information and files to support to the BOLD image database

Height Maps for surfaces

Height maps for the milled surfaces OGAB1-4, OISO1 and 2 and OSINE. These height map images were used to generate the milled surface for the surface photographs and they are registered with the photographs except that whereas the photographs have a border these image stop at the surface edge. Pixels in the height maps had side length = 0.045mm in the models. 1 grey level in the height maps corresponds to 0.001447mm in the z-direction of the models.

Colour space conversions

MatLab code for converting images from their LinearRGB format to sRGB, XYZ and lu'v' formats. The photographs in the database are colour balanced for the sRGB format but have 'linear to luminance' intensity values rather than gamma compressed values. A photograph of a ColorChecker chart (X-rite Inc MA; similar to a MacBeth colour chart) taken with our cameras and converted to lu'v' assuming standard illuminant A gives colour co-ordinates that are a good representation of the ColorChecker colours under a tungsten illuminant as measured with a SprectCAL spetroradiometer. Similarly outdoor images of the ColorChecker card converted to lu'v' assuming a D50 illuminant produce colour values that match those measured. Note our cameras have not been colour calibrated but when compared to a standard they seem to produce good results.

You can download comparisons between the colour rendition from our cameras and Spectroradiometer readings for the tungsten lights tungsten lights and for daylight. Note the linearity of the camreas can be verified in these spreadsheets although some saturation occurred for the white most tile of the ColorChecker in the outdoor case. You can also download the spectral characteristics of our light sources, including daylight.

Lighting Positions

Lighting positions and specifications for the object, surface and face photographs. Absolute sun positions (Azimuth and Elevation) are given for the external photographs along side the relative (ie relative to the camera) sun positions.

Camera Geometry, toe in and registration

The centres of he camera sensors were 95.4 mm apart. For objects and surfaces the cameras were toe'ed in by 4.2 each (8.4 total toe in). The viewing distance was was 645mm. For the portrait images the toe in was 2.2 (4.4 total). External images had no toe in.

Image pairs were registered as follows:

Surfaces: These were registered to a common rectangle using a projective transformation that removed trapezoidal distortions. Zero disparity corresponds to the mean depth plane of each surface.
Objects: We assumed objects to be broadly spherical and cropped images to place objects centrally. Thus zero disparity corresponds to the object centre.
Faces: The original image pairs varied slightly in scale (zoom) and orientation. We corrected these errors by applying equal and opposite transformations to the two images so as to bring the eyes into line. Equal and opposite transformations were applied to the two images in a pair. Zero disparity is at the middle of the nose and slighting inside the head (at eye depth) for the reference frontal pose image but people will have moved between photographs with different poses / lighting.
Outdoor: Slight differences iorientation were corrected by aligning two horizontal reference points between members of a pair and slight differences in scale (zoom) were corrected based on estimate from two vertically displaced reference points. Equal and opposite transformations were applied to the two images in a pair. The zero disparity plane is not well defined (the camera axes converged at infinity) but relative disparities are useful.

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