IPL Calibrated Color Image Database:
Natural Objects under CIE D65 and CIE A

About the Color Image Database

Why a NEW Color Image Database?

Calibration and Experimental Procedure

Database Organization & Download

Images and colors in the Database

Related Papers (citation of the database)

Colorlab (The Matlab Color Science Toolbox)

About the Color Image Database

The database
consists of 130 calibrated color images of natural objects under calibrated illuminations:
  • Calibrated images: images are given in CIE XYZ tristimulus values
  • Natural objects imply complex textures, mutual illumination and shadows, which induce non-linear effects in the tristimulus values.
  • Calibrated illuminations include diffuse CIE D65 and diffuse CIE A illuminant.
The database is suitable for accurate studies on color image statistics, chromatic adaptation in natural environments and color constancy.

Why a New Color Image Database?

This color image database was collected in the context of a chromatic adaptation study based on color statistics. In this context the following facts are relevant:
  • The proper way to describe the physical input to any (artificial or human) visual system involves either (i) absolute radiances, hyperspectral images, or (ii) absolute tristimulus images.
  • Even if the spectral reflectance of objects is known, the simple flat-Lambertian world assumption to estimate changes in tristimulus values when changing the spectral radiance of the illuminant is not valid in natural objects due to mutual illumination, shadows and specular reflections. For the same reason, estimating the reflectance by simply dividing the radiances by the spectrum estimated from a white reference sample in an hyperspectral scene is not correct either.
  • Accurate results on chromatic adaptation (as for instance, data on corresponding pairs) are usually given under controlled illuminants (e.g. CIE D65 and CIE A). In order to derive the psyhophysical behavior from color statistics under these illuminants, a wide enough ensemble of natural reflectances is required to have a continuous enough distribution of samples in the tristimulus space.
Many of the available image color databases have the following limitations related to the above issues:
  • Uncalibrated data (digital counts of conventional cameras instead of radiances or tristimulus values).
  • Spectroradiometric image databases do not generally include the reflectance of the objects, but it has to be estimated using a white reference sample. Even if the illuminant in some of the available images is similar to the required illuminant (e.g. CIE D65 or CIE A), the scene is not usually available under both illuminants. Even if you dont impose such a restrictive requirement (same scenes under both illuminants), but you just look for the same class of objects under both illuminants, you usually find that the databases are not large enough to ensure that the scenes under the desired illuminants include a wide enough set of similar reflectances.
  • The above is also true for the available tristimulus image databases.
In this situation, we decided to collect and make publicly available this calibrated database including a wide set of natural objects under a pair of calibrated illuminants.

Calibration and Experimental Procedure

We used a Macbeth Executive ligth chamber (Macbeth Inc.) equipped with standard CIE D65 and CIE A illuminants and we took the CIE XYZ pictures using a calibrated image colorimeter Lumicam1300 (Instruments and Systems Inc.) in the configuration shown below.
Experimental Setting

CIE D65 Illumination           
            CIE A Illumination

In every picture the exposure time for each filter (X,Y,Z) was adjusted to avoid over or under exposition in order to ensure the picture was taken in the optimal operating range of the camera. Pictures with misregistered channels (due to motion) and scenes outside the operating range of the camera (very dark and very bright regions in the same scene) were discarded.

The accuracy of illuminants and measurements was checked by taking pictures of 10 hues pages of the Munsell Book of Color. We checked the accuracy in chromaticity by comparing the measured CIE xy chromaticities with those computed from the known reflectances of the samples and the known spectral radiance of the illuminants. In this case (flat matte samples) we neglected geometrical factors and applied the flat Lambertian assumption in the theoretical prediction. Experimental and theoretical results are shown below. Luminance accuracy was checked with a PR-670 SpectraScan spectroradiometer on the standard white background of the pages of the Munsell Book of Color.
The accuracy in luminance was roughly within the limits provided by the manufacturer (~3%).

Organization of the Database

The database includes 65 different scenes of natural objects under two illuminants (130 images) plus 10 scenes displaying different hue pages of the Munsell Book of Color (20 images). The image size is 1000x1280 pixels. The images are classified as follows:

Download Files
matlab images_munsell_D (.mat - 273Mb)  
matlab images_munsell_A (.mat - 273Mb)
Calibration set (20 Munsell Images):
10 hue pages of the Munsell Book of Color (20 images), mainly matte flat surfaces without mutual illumination.

matlab images_natural_I_D (.mat - 1,36Gb)
matlab images_natural_I_A (.mat - 1,36Gb)
Natural Objects I (100 images):
Scenes of colored textures with complex spatial geometry (non-flat surfaces).
28 scenes of plants and flowers (56 images),
13 textured natural materials (26 images),
9 samples of textured colored fabric (18 images).
matlab images_natural_II_D (.mat - 416Mb)    
matlab images_natural_II_A (.mat - 417Mb)
Natural Objects II (30 images):
Scenes of office material with simple spatial geometry (mainly flat surfaces including bright objects).
matlab readme_database (2kb) How to load the database in Matlab:
See the sample file readme_database.m on how to read the images.
matlab IPL_color_image_database (.zip - 4 Gb)
Download the complete dataset (all the above files):

Images (Matlab arrays of size 1000x1280x3) are stored in a Matlab structure in each of the corresponding *.mat files above.  Images in the structure are sorted according to the order in the pictures below. Chromatic diagrams with all the colors in each set are also shown below. For your convenience we include a file to load the images in Matlab.

Calibration set (20 Munsell Images)

Blue: experimental Munsell colors under CIE D65 illuminant (above pictures).
Black: theoretical Munsell colors under CIE D65 illuminant.
Yellow: experimental Munsell colors under CIE A illuminant (above pictures).
Red: theoretical Munsell colors under CIE A illuminant.
Natural Objects I

colordgm_real_I_D colordgm_real_I_A
"Natural" Objects II

colordgm_real_II_D colordgm_real_II_A

Related Papers (database citation)
Colorlab (The Matlab Color Science Toolbox)

If you found this database interesting, you may be probably interested in accurate colorimetric computation in Matlab. Please check this link for more information on COLORLAB: The Matlab Color Science Toolbox!.