Outline: Metering!

• What makes metering hard? ! – the meter doesn’t know what you’re looking at ! The Art, Science and Algorithms • histograms ! – Rule of thumb! of Photography! • metering technologies ! • metering modes (center, evaluative,...) shooting modes (Av, Tv, P, M) ! Exposure & Metering! • exposure compensation! CSCI 4900/6900! • background topics ! – Ansel Adams’ zone system! Maria Hybinette! – Zone system and digital photography! • Quiz!

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Quiz: Metering! What Makes Metering Hard?! 1. On Auto: you metered black on black (BB), white on white (WW) and grey on grey (GG): How did the images differ?! • light meters are not magical they don’t know 2. For black subject on white background (WSWB), Which what you are looking at & what you want.! metering from (1) worked best?! 3. For a white subject on a black background (WSBB) Which • so they assume the scene is “middle” gray metering from (1) worked best?! (18% reflective) [12%-14%]! 4. Assume you had reading available from (BB), (WW) and (GG) • the world is full of hard metering problems...! but now your meter is broken:! a) For a black subject on a white background (BSWB) how would you expose your image? [you can still adjust shutter and aperture)! b) How about a white subject black background?! 5. Suppose you did not have a metered reading for (GG) but only for BB and WW, how would you now expose BSWB and 3! WSBB?! 4!

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Metering Modes! Shooting Modes!

• Centered average! • Aperture priority (Av, A)! • Spot! – Photographer sets aperture (so depth of field) an! – Camera sets shutter! • Smart metering! • Shutter priority (Tv, S)! – Learn from database of images (Nikon 30,000 images) , – Photographer sets shutter (so motion blur)! decision process may depend on:! – • How much brightness from different “areas” of grey?! Camera sets aperture! • Local contrast, where is the subject, foreground, background! • Program (P)! – Nikon 3D matrix (multiple segments)! – Camera sets both, some trade-off options! – Canon evaluative! • Manual (M)! • Incident (hand held light meter)! – Photographer sets both (must meter)! – Histogram may help! – Measure incoming light! !"#$%%&&&',0/1*3;4.36,)2)-*',)/%+-+)*302(%!3(+)4*0/(7'!+/:

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Histograms (simplified for now)! Idea!

11! 12! White on White: High Key! What the Camera Did!

• Underexposed originally left (made it grey)!

13! 14! • Corrected on the right!

High Key! Low Key!

• Rule of thumb:! – End up with underexposed images! • No blown (or clipped) channels or highlights! • More forgiving! – Higher signal to noise!

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Low Key!

• Prone to overexposure! • Details cannot be recovered.!

• Overexposed: clipped/blown channels!

17! 18! Contrast! Quiz 2!

• Narrow range low contrast e.g., (fog no texture on the left)! • Broad range, high contras e.g., (texture water with a range of tones).! 19! 20! !"#$%%&&&';0/3.6(@/)6;(',)/'0-%+-+H!3(+)4*0/'!+/2:

Quiz 2: Answer! Impossibilities!

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21! !"#$%%&&&';0/3.6(@/)6;(',)/'0-%+-+H!3(+)4*0/'!+/2: 22!

What to do?! Bad Histograms?!

• Fill flash ! • Graduated Neutral Density Filter! • Take multiple exposures (and blend)! • But a better camera (film) or a Nikon D3X! • Go home!

23! 24! How much latitude in Camera?! Film Exposures!

• Make sure you are exposing the important • Nine stops (each stops is double in brightness from its areas within the film latitude! neighbor) contrast range, plus all black and all white! – Underexposing darkest will fall off! – (12 stops Hasselblad, 10 stops Nikon D3X)! – Overexposing you get flat areas without contrast • Seven stop contrast range, plus all black and all white! (no texture)! • Five stop contrast range, plus all black and all white ! !"#$%%&&&'B)*#!)+)4*0#!@',)/%!)&8+)(%J)6.%J)6.7'!+/225! : 26!

Film! Film Exposure!

• Exposure controls shadows! • Best to expose for the shadows, to the left! • Development time controls the highlights! – Also: the higher the contrast, and the greater the difference between black and white. ! • Rule of thumb, ideal exposure is to place all the tones of the object except all black, just within the films threshold to the left. ! – Allows for smallest aperture! – Not too dark! – Fine grain, !

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Digital Exposure! Zone System!

• roughly 1 f/stop per zone! • Expose to the left: Danger Noise!! • X = “maximum white of the paper base”! • IX = “slight tonality, but no texture: flat • Digital cameras have disproportional fewer darker snow in sunlight”! • VIII = “textured snow, lightest wood at tones than we see with our eyes (lots of bright tones)! right” ..... [digital exposure]! • Full tonal range of scene:! • VII = light/pale skin tones ! • V = 18% gray card, sky, light foliage! • III textured shadows [film exposure]! • II first hint of texture! • I stuck with these cant contract or expand after exposure.! • 0 = “maximum black that photographic paper can produce” ! • lesson for the digital age! !"#$%%&&&',0/1*3;4.36,)2)-*',)/%+-+)*302(%;343+028.?#)(-*.8+.,!63K-.('!+/29! : 30! Left to talk about!

Exposure/Metering! • Gamma! – S/N! • Bits / RAW and dynamic range! • HDR (beginning)! Next up:! • Lenses, focal lengths, distortion and DOF ! • Camera hacking !

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Quiz: Metering! 1. On Auto: you metered black on black (BB), white on white (WW) and grey on grey (GG): How did the images differ?! 2. For black subject on white background (WSWB), Which metering from (1) worked best?! 3. For a white subject on a black background (WSBB) Which metering from (1) worked best?! 4. Assume you had reading available from (BB), (WW) and (GG) but now your meter is broke! a) For a black subject on a white background (BSWB) how would you expose your image? [you can still adjust shutter and aperture)! b) How about a white subject black background?! 5. Suppose you did not have a metered reading for (GG) but only for BB and WW, how would you now expose BSWB and 33! WSBB?! 34!

Slide Credits/Resources!

• Prof. Fredo Durand! • Prof. Marc Levoy! • London, Stone, Upton Textbook! • Wikipedia! • http://www.luminous-landscape.com/tutorials/expose-right.shtml! • http://www.cambridgeincolour.com/tutorials! • http://www.bythom.com/graycards.htm! – ANSI standard is 12% gray (1/2 stop less than 18% gray on Kodak Gray Cards).! – http://david.spielman.com/Gray_Card/ ANSI_PH3_49_1971.PDF!

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