dimana <math>V_{out}</math> dan <math>V_{in}</math> adalah relasi bolak balik ([[bahasa inggris|en]]:''reversal'') antara reaksi substrat perak nitrat pada negatif film dan iluminasi yang mengenainya. Relasi ini dipetakan menjadi diagram yang disebut '''characteristic curves''',<ref>{{cite web | url = http://www.kodak.com/global/en/professional/support/techPubs/f4017/f4017.jhtml | title = KODAK PROFESSIONAL TRI-X 400 Film / 400TX | Kokak Professional Support}}</ref> '''Hurter–Driffield curves''',<ref name=palmer/> '''H–D curves''',<ref name=palmer>{{cite book|title = Advanced University Physics|author = Stuart B. Palmer and Mircea S. Rogalski|publisher = Taylor & Francis|year = 1996|isbn = 2884490655|url = http://books.google.com/books?id=TF6Igz5lJLgC&pg=PA349&dq=hurter-driffield-curve+h-d-curve&lr=&as_brr=3&ei=songR5KAJIWusgOWlPQU&sig=FgC6_uAklssPUpNaUyyr2lS0hNk }}</ref> '''HD curves''',<ref>{{cite book|title = Multielement Detection Systems for Spectrochemical Analysis|author = Kenneth W. Busch and Marianna A. Busch|publisher = Wiley-Interscience|year = 1990|isbn = 0471819743|url = http://books.google.com/books?id=9H0W1J-Rku4C&pg=PA339&dq=h-d-curve+density&lr=&as_brr=3&ei=qYzgR46lBYbosQOrzpgV&sig=_kTikTsCw2-7B8XvfO6y73rmTkc#PPA341,M1 }}</ref> '''H & D curves''',<ref>{{cite book|title = Principles of Radiographic Imaging: An Art and a Science|author = Richard R. Carlton, Arlene McKenna Adler|publisher = Thomson Delmar Learning|year = 2000|isbn = 0766813002|url = http://books.google.com/books?id=oA-eBHsapX8C&pg=PA318&dq=h%26d-curve+density&lr=&as_brr=3&ei=to3gR5GCLI6eswOs98kV&sig=s_vE4f5PMysrrCtgM7_HJrsRu_Y }}</ref> '''D–logE curves''',<ref>{{cite book|title = Remote Sensing Geology|author = Ravi P. Gupta|publisher = Springer|year = 2003|isbn = 3540431853|url = http://books.google.com/books?id=74T8X1zqgF4C&pg=PA62&dq=d-log-e-curve+density&lr=&as_brr=3&ei=eY7gR4qWEILusgO60YCrAg&sig=MBImrU6KwlZwoV29Xl1PywwEINQ }}</ref> or '''D–logH curves'''.<ref>{{cite book|title = The Focal Encyclopedia of Photography|author = Leslie D. Stroebel and Richard D. Zakia|publisher = Focal Press|year = 1993|isbn = 0240514173|url = http://books.google.com/books?id=CU7-2ZLGFpYC&pg=PA794&dq=d-log-h-curve+density&lr=&as_brr=3&ei=BI_gR6qIGIiUtgOY5tEV&sig=wfoH3l-C-AKifDLLObbnYn7FrHg }}</ref>.
Diagram ini mempunyai rentang linear yang disebut gamma. Pada rentang linear tersebut berlaku:
sehingga variabel <math>\gamma</math> disebut '''gamma correction''' atau '''gamma nonlinearity'''.<ref>{{cite book|title = Digital Video and HDTV: Algorithms and Interfaces|author = Charles A. Poynton|publisher = Morgan Kaufmann|year = 2003|isbn = 1558607927|url = http://books.google.com/books?id=ra1lcAwgvq4C&pg=RA1-PA630&dq=gamma-encoding&lr=&as_brr=3&ei=WHfDR6q4J4OmswOGiZXPDw&sig=OYiWf7BJ2ACTek1UAsbcXOIlvP0 }}</ref> Pada saat <math>\gamma > 1</math> sering disebut '''expansion gamma''' atau '''decoding gamma'''. Sebaliknya pada saat <math>\gamma < 1</math> sering disebut '''compressed gamma''' atau '''encoding gamma'''.
=== Pemetaan (''data binning'') densitometri ===
Baris 68:
spectra) of human cone cells, S, M, and L types]]
'''Densitometri''' merupakan kuantifikasi respon daya serap suatu medium perak nitrat pada film terhadap iluminasi yang mengenai permukaannya. Jika pada gamma menunjukkan akumulasi partikel perak nitrat, pada densitometri menunjukkan penurunan iluminasi akibat akumulasi substrat tersebut. Nilai logaritmik dari resiprok transmisi cahaya yang didefinisikan sebagai ''absorbance'' atau ''density''<ref name=davies>{{cite book|title=The Focal Digital Imaging A-Z|first=Adrian|last=Davies|url=http://books.google.com/books?id=j7l0CxBUwGwC&pg=PT44&dq=density+dmax+dmin+logarithm&ei=2j23R7OwKJbWzAT4gpXGBQ&sig=DqqcRgdi1GeJs_J5GnzBIS3ZB44|publisher=[[Focal Press]]|isbn=0240519809|year=2005}}</ref>. yang serupa dengan respon visual (''spectral sensitivity'') manusia pada ''rod cell'' dan ''cone cell'' retina mata yang disebut ''scotopic vision'' dan ''photopic vision''. Pada [[fotografi]], film dan sensor sering dijabarkan dengan menggunakan istilah ''spectral sensitivity'' untuk menjelaskan karakteristik respon bersangkutan terhadap iluminasi.<ref>{{cite book|title = Advanced Photography|author = Michael Langford|publisher = Focal Press|year = 1998|isbn = 0240514866|url = http://books.google.com/books?id=Z92UjOE93SIC&pg=PA73&dq=%22spectral+sensitivity%22+intitle:photography&lr=&as_brr=3&sig=2Ex5bPhpeRKM-lqFd1uACWiD06Q }}</ref>
