Red and Blue

by Gordon

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1

This question is tagged "history" so, some history -- Photographs (of course) don't have to be literal captures of a scene. Plenty of photographers (past and present) have manipulated the image to reflect their feelings about the subject (or other stuff). Pre-digital (and really, before desktop computer image editing -- which pre-dates pure digital ...


2

My understanding is that 18% grey is considered the average reflectance of light from the world around us - not snow (about 90%) or a black cat in a coal mine at the other end, but an average on an average day. Grass, for example, reflects about 18% grey, so if you are reading your meter you can take a reading off the grass and then calculate from there. ...


1

I'd like to add that eyes and silver halide emultion naturally have a logarithmic response, unlike CCD/CMOS sensors, for the same underlying reason. Consider a patch of molecules spread over the focal plane. An incomimg stimulus (two photons hitting the crystal in a certain time window, in the case of film) is recorded by changing the state of that molecule ...


4

Even beyond perceptual issues, film exposure latitude is another reason to favor 18% gray. If one tried to expose a scene so that the average gray tone on the scene would yield an exposure value of 50%, then anything which was even twice as bright as the average would get totally blown out. If one tried to expose a scene so that the average gray tone on ...


13

It's worth looking at a gamma chart for additional perspective as you think about this. Standard display gamma, for example, is 2.2. The curve looks like this: 50% grey, in an 8-bit space, is 127 (horizontal axis). This lines up with ~20% luminance output of the display. Both for display and print the concept of gamma is important as it provides the ...


16

The story goes that Ansel Adams came up with the "18% gray" figure. Back in the hay day of film photography he was developing the zone system and needed to define a "middle gray". It was a judgement call. Eventually, the idea caught on, but film and camera companies picked their own middle gray. It is a fun fact that your digital camera probably uses ...


1

Looking at http://www.firstcall-photographic.co.uk/userfiles/file/faultsonblackandwhitenegatives.pdf and http://www.olympusmicro.com/primer/photomicrography/bwprocessingerrors.html it could be one of the following things (or even combinations thereof): Underexposure Underdevelopment Inadequate fixing Variations in processing temperature (reticulation) If ...



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