Frequently Asked Questions

• What is the BTF and BRDF?
  The BTF datasets consist of a collection of material images taken for thousands of lighting and viewing (bidirectional) directions. Such data can be used for appearance rendering on arbitrary objects under arbitrary lighting and viewing conditions. BRDF can be viewed the same way, but instead of images storing only RGB triplets. Therefore, its storage space demands are substantially lower.
• What instrument do you use for measurement of materials appearance?
  Our 4-axis gonioreflectometer was developed at our department in 2011 and its abilities are steadily improving. It allows precise setting of arbitrary illumination and viewing directions with repeatability 0.03 degrees. Typically RGB HDR data are recoded, but spectral measurements are possible too. In frontal view a single pixel records spatial area of 46x46 um. You can see video at homepage or contact us for more information.
• What is the database of material good for? Is it just for rendering?
  Our database was created to provide data for material visualization in film and gaming industry, or for industrial visualization of materials (fabric, leather, wood finishes, effect coatings, etc.). However, one can use it also for general analysis of material appearance. Our data can be also used for development of material quality control methods or anywhere, where you need trustworthy digital information about visual qualities of material surface.
• Why is your database better than the common material libraries and galleries?
  If you need realistic appearance of a particular material on a 3D model, it is often difficult to achieve it faithfully with standard methods. The materials in our database are real materials measured by gonioreflectometer. As confirmed by our psychophysical research, the method is the most reliable with respect to the real appearance of the material. BTF measurements provide you with a natural look-and-feel of materials. Feel free to join the group Material Appearance - Psychovisual Studies on LinkedIn to learn more about advantages of using the bidirectional datasets.
• Are your materials free for commercial use?
  Our public datasets are free of charge for the non-commercial use only. Please, contact us if you want to use them for commercial purposes. Mention the extent of your business and the purpose you want to use our data for.
• I have filled dowload form but have not received the data yet!
  We are sorry for any inconveniences, the requests are handled individually and download links are typically sent within 24 hours. Please, send a short reminder to btf @ utia . cas . cz if your request is not resolved within this time.
• I have my own material. Is it possible to measure it?
  Yes, it is possible to measure your own material appearance. Feel free to contact us. For price quote of the measurement we would like to know the number of materials, their character, the required representation (BTF/BRDF/...) and angular density. We are located in Prague (Czech Republic). You will have to send/bring us the samples. Once you are happy with the measured data visualization, we can proceed with agreement.
• My material is rough/shiny/specular/transparent/metallic/colorful etc. - is it a problem?
  No, in general it is not a problem. Exceptionally, it may happen that some specific appearance aspects are captured with limited realism. We can measure nearly any type of material and provide you with data, so as your renderings could be as realistic as possible.
• What format are the data you provide?
  This depends on specific datasets you are interested in. BTF data are stored either as a collection of images or in a binary formats with meta-information (.big). BRDF data are offered as OpenEXR images (.exr), Matlab (.mat), or binary files (.bin). Data reading and handling codes are provided when needed. BTF data can be at individual request compressed and stored in a format (.btf) for Autodesk VRED or 3Dexcite Deltagen.
• Is it possible to use your data with my software (e.g. Blender/Maxwell/Autodesk?)
  We do not provide direct support to any rendering software; however, third party public SW exist that allows using datasets (e.g. BRDF plugin to Mitsuba renderer), BTF plugin to Autodesk VRED. Moreover, anyone is welcome to write its own plugins to rendering SW using the codes provided.
• Do you have any references? Who does use your data?
  Please contact us to get the references.