I can not find the word luminance in my dictionary. Luminescence
Originally Posted by jdef
I can find; an emission of light. Do I need a bigger dictionary? Dan
From The Focal Encyclopedia of Photography:
Originally Posted by dancqu
The visual experience that is approximately correlated with the luminance of objects seen as light sources. Since brightness is a psychological concept, there are no units of measurement as there are for luminance, a psychophysical concept.
L. Stroebel and R Zakia
The quotient of luminous intensity of an extended surface in a specified direction by the projected area in that direction (i.e., candelas per square meter). The luminance of an extended source or surface is invariant with viewing distance. Luminance is also invariant within a lossless optical system because changes in image size are balanced by inverse changes in solid angle. The luminance of a Lambertian (ideal) diffuser is invariant with viewing angle because the reduced power reflected off-axis is balanced by a reduction in projected area.
Luminance is the property of a source of surface that most closely correlates with the subjective perception of brightness, which, because of adaptation and contrast effects of the visual system, cannot be used as a reliable measure.
Syn: photometric brightness (obsolete)
Last edited by Stephen Benskin; 04-14-2005 at 09:58 PM. Click to view previous post history.
Luminance is that quality of a finished print that makes it seem to light up the room it's in. Yes, good topic and a lifetime to learn. I was thinking along these lines today. I bought a set of filters that are no longer made. Colored polarizers (g-y-r-bl) and I was looking at each one trying to decide what the different effects would be on B&W film. It's something that's not as easy for me as some other aspects are.
Reading last night in Adams book 5 on artificial light and his take on luminance was refreshing. He compared brightness and luminance in very simple terms.
His explanation of brightness deals with the inherent property of reflected light from an object, without necessarily dealing with the amount of light directed at it. A side in shadow reflects x amount of light and a side in full light reflects y amount of light, simple zone system parlance and metering.
His take on luminance deals not with the reflected light from surfaces, but with the light falling upon it. He then explains how light intensity can be manipulated (additive or subtractive) to allow for creative interpretation of a given subject in a finished print. It really is a shame he died so soon, as his understanding of light and the ability to explain it was wonderful.
I would have liked to have seen him in a discussion of techniques with Phil Davis. We owe both of them a huge debt.
Thanks Jay for starting this thread. I believe this is an important topic. We all have a tool box of techniques that we carry with us when shooting, so why only use the same one or two tools? It is just part of visualization after all. The problem is to find a good example to start.
For very short luminance ranges.
I have this image of a detail of a gravestone. It was late in the day. The weather was dark, windy, and with light rain. It was a typical day in Ireland. The stone had almost no separation. The light was so soft, there was virtually no "shadows" cast.
I wanted the final image to be very dark where it looked almost totally black until you walk up to it. I decided to place the exposure of the stone just under the midpoint, or about Zone IV. Even though I wanted the image dark, I didn't think it would work without a lot of local tonal separation. Extended processing has more of an affect on the upper part of the curve than the lower, so in order to maximized the amount of tonal separation with processing, I placed the exposure higher on the curve than I needed knowing I could print it down. I gave the film +2 development knowing it wouldn't be sufficient, but also knowing I could print it on a grade four paper and use a number of additional techniques if needed.
It did print on a grade 4, and I did just a touch of bleaching to emphasis a few places. Why not just push the film 4 stops? Three reasons: One, extended processing of film increases the higher densities to a greater proportion than the mid tones and shadows, whereas increasing the paper grade expands the mid tones to a greater extent. Two, the undesirable factors that come with pushing film such as grain. Three, it's also extremely difficult to visualize how all the elements will look at such an extreme contrast increase. Not over processing gives you more options.
One of the problems of extremely expanding short luminance ranges it that areas that you don't want to expand, also expand. Sometimes this creates looks of small annoying white spots, and sometimes it makes the overall image look harsh.
Some times it's easy enough to spot out the annoying stuff. I have an image of a burnt wall which I handled in a similar manor as the gravestone. It takes two hours to spot out the new created highlight speculars that now look like dust.
One way to fix that problem and when the image looks overly harsh is to deal more with only the tones you want to change. A good example is rock art. Petroglyphs are drawings created by etching through the desert patina to expose the lighter rock underneath. The contrast range is very limited, but often the sun is hitting the rock creating a normal luminance range or at least expanding the luminance range some. The question is how much can you push the film before the image just looks too contrasty and unrealistic? Using the above technique might work in certain conditions, and look harsh in others. A good way to approach such a scene is to give it normal or +1 processing, and then print it so that the rocks look natural. At this point, the petroglyphs will still look flat.
Off the top of my head, two techniques can help here. One is to use a contrast mask while printing the image. The mask will add density only to the areas you want. This will lighten up the drawings without adding contrast to the rocks. Another way is to bleach. Take a paint brush and paint over the drawings using potassium ferricyanide until they reach the point you want.
The concept that I like with this thread is that this is where theory (such as tone reproduction theory) meets creativity. It is the very essence of photography. Nice idea Jay.
Here's an interesting question. Except for special cirumstances, all scenes look best in a print when there is a full range of tones. Why can't we let a flat scene remain flat in the print (apart from artistic considerations)? It's flat in nature, why not the print? Maybe a question for another thread.
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One further thought. Mr. Robert Pace, a very experienced printer has these thoughts about making a more interesting print.
Use color transparency film.
Contrast mask the film with one color light
Make your negative with the mask in place using a second color of light.
His contention is that this method allows for far greater manipulation of tone reproduction than just the use of a B&W film in conjunction with a filter.
These thoughts are stated in his self-published book "Masking" which is the best reference that I know about on the subject of masking.
I apologize for being somewhat off topic but it seemed to fit the discussion at hand.
You're not at all off topic. Do you have information where the book can be purchased? My concern about Pace's method is that you lose a generation with the negative. Sounds like a good read though.
Originally Posted by Claire Senft
That's a great description of Applied Adams, Stephen. After that, I've become very curious to see what the result looked like! Any chance of posting it?
Originally Posted by Stephen Benskin
If you tone it down alot, it almost becomes bearable.
- Walker Evans on using color
It is exactly applied Adams, as Adams was applied tone reproduction, as tone reproduction is, well, tone reproduction. My thoughts are this is the culmination of all the technical knowledge we struggle to learn.
Originally Posted by NikoSperi
The image might not translate well here because it isn't about a full range of tones. One point I forgot to mention in the previous post is that the original, very flat, subject was primarily light gray.
Last edited by Stephen Benskin; 12-02-2007 at 01:32 AM. Click to view previous post history.
Cool, thanks for that. As they say about the thousand words and an image... I'm just starting to explore the extent of "interpretation" one can give to an exposure and development. The Adams book The Print has a fern on the cover. I have tried to replicate that fern with the same film under the same conditions. You really need to stretch the envelope to take a one-stop scene and turn it into a multi-toned print. Good job and thanks for sharing the how-to and the result.