ASTM_E_2729_-_09_2015.pdf

Designation:E272909(Reapproved 2015)Standard Practice forRectification of Spectrophotometric Bandpass Differences1This standard is issued under the fixed designation E2729;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This standard outlines the methods that can be used todeconvolve,at least partially,the spectral bandpass differencesof raw spectral data acquired by abridged spectrophotometry.Such differences are introduced because the spectral passbandmust be of significant bandwidth to allow sufficient energy toreach the detector.On the other hand,the spectral data thatshould be being reported is that of a virtual 1-nm bandwidthspectrum in order to be useful in the CIE method of tristimulusintegration which involves 1-nm summation.1.2 The standard establishes practices for whether,when,and how a bandpass rectification should be made to anyreflectance or transmittance spectrum acquired by abridgedspectrophotometry.1.3 It is applicable where the shape of the passband istriangular and the bandwidth is equal to the measurementinterval between passbands.Information is provided in Section7 for users when that condition is not satisfactorily met.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2E284 Terminology of AppearanceE308 Practice for Computing the Colors of Objects by Usingthe CIE System3.Terminology3.1 DefinitionsFor definition of terms used in thispractice,refer to Terminology E284.3.2 Definitions of Terms Specific to This Standard:3.2.1 virtual 1-nm bandwidth spectrum,nspectral datathat have been corrected by numerical methods so as to matchas closely as possible a spectrum from the same source but witha putative bandwidth of 1 nm.4.Summary of Practice4.1 The practice assumes that the shape of the passband istriangular and that the bandwidth is equal to the measurementinterval between passbands.This condition is thought to be metby a majority of commercial instruments in use in spectropho-tometry and spectrocolorimetry.Under those conditions,themethods of Section 6 are to be utilized to rectify the rawreflectance or transmittance data for its bandpass differencesimmediately upon the return of the data to the host computerprogram from the acquiring instrument,or before presentationof the data to the user.5.Significance and Use5.1 Failure to make such a rectification introduces differ-ences from the true value of the spectrum of about 0.02 to 0.4E*abunits.All users are required to make a rectification ofsuch bandpass differences.It is especially incumbent uponwriters of computer programs whose function it is to acquiresuch spectra from instruments to see that a competent rectifi-cation is implemented in the program before any additionalprocessing of the spectrum,or calculations involving thespectrum are accomplished,or before the spectrum is madeavailable to a user.5.2 Legacy measuring systems are explicitly exempted fromany requirements for retrofitting of hardware or software andmay continue to utilize previously accepted methods of makingthe bandwidth rectification.6.Methodology6.1 The First and Last PassbandsIn the first and lastpassband being rectified,no correction is called for.Thecorrected spectral value Rs,should be set equal to themeasured spectral value Rm,.Rs,15 Rm,1(1)Rs,n5 Rm,n1This practice is under the jurisdiction of ASTM Committee E12 on Color andAppearance and is the direct responsibility of Subcommittee E12.04 on Color andAppearance Analysis.Current edition approved April 1,2015.Published April 2015.Originallyapproved in 2009.Last previous edition approved in 2009 as E2729 09.DOI:10.1520/E2729-09R15.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 where the subscripts 1 and n refer to the wavelength index ofthe first and last passbands being corrected.6.2 The Second and Next-to-last PassbandsThe secondand next-to-last passbands being rectified are subject to thefollowing correction:Rs,25 20.10Rm,111.21Rm,22 0.12Rm,310.01Rm,4(2)Rs,n215 20.10Rm,n11.21Rm,n212 0.12Rm,n2210.01Rm,n23where the second subscript refers to the wavelength index ofthe bandpass considered.6.3 The Remaining Interior PassbandsThe remaining in-terior passbands are subject to the following five-point rectif