Traditionally, the AToB0 tag of an ICC printer profile, containing the perceptual transform from device specific to PCS
Lab or XYZ values, has been generated directly from measurement data without considering the color re-rendering
included in the PCS to device-specific transform found in the corresponding BToA0 tag. In this case, the AToB0 color
conversion will often not be the inverse of the color conversion in the BToA0 tag. However, with ICC version 4, the
AToBn and BToAn transforms are in general supposed to be inverses of each other, to the extent possible. This feature
supports the re-purposing of color data within an ICC color management workflow. This inversion is a challenge for
profile generation due to issues with either directly inverting 3-D interpolations or inverting every step applied in
generating the BToA0 tag. Directly inverting a 3-D LUT may not be feasible because the forward mapping is usually
not a one-to-one mapping. Mathematically, inverting every operation for generating a BToA0 tag may also be
extremely difficult if not impossible. Consequently, a closed-loop method has been developed which iteratively adjusts
AToBn tags to improve the invertibility of ICC profile transforms. The test results are very encouraging.
Newly developed standard terminology enables improved communication about color processing objectives and research goals. By clarifying specific color processing tasks, one observes that there are de-facto standard practices for many processing steps, that can be used as a baseline recommendation for implementers and future development work. The more explicit descriptions of development goals can also serve to focus research on the desired objectives. This increased clarity leads to work being both more effective at meeting design objectives, and also more apparently relevant to commercial applications. Differences in objectives and requirements for the development of color rendering and gamut mapping algorithms are discussed and contrasted. In some cases, these differences can explain the reasons for different approaches, enabling broader consensus and understanding. Differences between color appearance and reproduction models are also discussed, along with the impact of these differences on their use for imaging applications. The above concepts are related to important color reproduction considerations, such as the preference and media capabilities. If the more explicit terminology is widely adopted, it could accelerate the advance of digital color understanding across both product manufacturers and users, and enable significantly more effective research, development, and use.
The ISO TC42/WG18-20-22-23 and ANSI/I3A IT10 Technical Committees have now been developing digital photography standards for over a decade. This work has led to the publication of standards on digital imaging terminology, digital camera ISO speed measurements, resolution measurements, OECF (linearity) measurements, image formats and metadata, and picture transfer protocol (PTP). More recently, standards on color encoding specifications and color architectures, a JPEG 2000 profile for digital cameras, camera noise and dynamic range measurements, digital camera specification reporting, and scanner resolution have been finalized. Work in progress includes image quality subjective testing methods, digital camera color characterization, and scanner dynamic range measurements. This paper will review past and current technical challenges, and the state of the solutions provided. In most cases, development includes a significant and innovative research component, which is discussed in relation to fundamental imaging issues. These standards are viewed from a broad digital photography perspective, and placed in context with other work in this area. In addition to providing a forum for the development of standards, technical committees are an important avenue for interaction between companies, user groups, and the government. Such avenues can have a great impact on emerging technologies.
Chromatic adaptation transforms are used in imaging system to map image appearance to colorimetry under different illumination sources. In this paper, the performance of different chromatic adaptation transforms (CAT) is compared with the performance of transforms based on RGB primaries that have been investigated in relation to standard color spaces for digital still camera characterization and image interchange. The chromatic adaptation transforms studied are von Kries, Bradford, Sharp, and CMCCAT2000. The RGB primaries investigated are ROMM, ITU-R BT.709, and 'prime wavelength' RGB. The chromatic adaptation model used is a von Kries model that linearly scales post-adaptation cone response with illuminant dependent coefficients. The transforms were evaluated using 16 sets of corresponding color dat. The actual and predicted tristimulus values were converted to CIELAB, and three different error prediction metrics, (Delta) ELab, (Delta) ECIE94, and (Delta) ECMC(1:1) were applied to the results. One-tail Student-t tests for matched pairs were calculated to compare if the variations in errors are statistically significant. For the given corresponding color data sets, the traditional chromatic adaptation transforms, Sharp CAT and CMCCAT2000, performed best. However, some transforms based on RGB primaries also exhibit good chromatic adaptation behavior, leading to the conclusion that white-point independent RGB spaces for image encoding can be defined. This conclusion holds only if the linear von Kries model is considered adequate to predict chromatic adaptation behavior.
This paper presents a comparison between primary (RGB) and complementary (CYMG) CCD color filters arrays, as applied to digital photography. Our analysis is based upon the measured spectral characteristics of the primary and complementary color versions of the Matsushita MN3776 CCD. The important role of the color correction matrix on the quality of the image is considered both in terms of noise and color saturation. Our calculations show that there is a tradeoff between color saturation and ISO speed, when complementary filters are used. Complementary color filters only gain an ISO speed advantage when the color saturation is low. When the color correction matrix is chosen to make the ISO speeds of the two filter systems equivalent, the well capacity of the complementary CCD must be significantly higher because of the higher overall transmission of its color filters. Our comparison includes ISO speed calculations and plots of the color gamut for primary and complementary color filters with various color correction matrices. We conclude that primary color filters are superior for digital photography.
The ISO TC42/WG18 and ANSI/NAPM IT10 Technical Committees are developing the following standards related to electronic still photography: ISO 12231 - Glossary of technical terms; ISO 12232 - Determination of ISO speed; ISO 12233 - Resolution measurements; ISO 12234 - Removable memory; and ISO 14524 - OECF measurement methods. ISO 12231 is at the DIS stage, ISO 12234 and 14524 are at the CD stage, and ISO 12232 and 12233 will most likely reach the CD stage within a year. Since most of these documents are approaching final form, it is useful to examine them in some detail.
Presented here are summaries of the contents of these standards accompanied by comments on their application and state of development. These standards are viewed from a broad digital photography perspective, and placed in context with other work in this area. Significant research has been accomplished in these committees, and is discussed in relation to fundamental imaging issues. Also discussed are future projects and areas where standardization is needed but little has been accomplished. In addition to providing a forum for the development of standards, technical committees are an important avenue for interaction between companies, user groups, and the government. Such avenues can have a great impact on emerging technologies.
A data sheet is presented outlining the performance and characteristics of a Kodak DCS 200mi camera. In addition to providing information on this camera, the format and content of the data sheet could serve as a guide in the organization and display of pertinent information on electronic still cameras in general. Such data sheets are already common in silver halide photography. Pictorial electronic still photographers could benefit greatly from the publication of data sheets which enable them to judge the possibilities and limitations of the hardware and software. The proposed data sheet will contain descriptive specifications and numerical values such as sensor type, active sensor area, photoelement size, fill factor, filters, normal lens focal length, lens MTF, shutter type, shutter speed range, exposure metering modes, image storage, data output, compression, saturation speed, noise equivalent quanta (NEQ) speed, resolution, spatial frequency response (SFR), optoelectronic conversion function (OECF), noise power spectrum, effective bit depth (and spatial frequency dependence), peak equivalent image quality (EIQ) values, spectral response, etc. Where appropriate, the numerical values will be calculated according to the developing ISO standards in electronic photography. The graphical format of the data sheet as well as the information depth will be discussed.