I want 18% middle gray what do I tell the paint guy at home depot?

wolves3012 said:
Artists paints Roger...apples...oranges ;-)

Not heard the joke, that made me chuckle!

Actually, for most commercial paints, specifically domestic paints, the simplest way is to add a matting agent (usually silicas) to a gloss formula. Often there's also china clay added because it also reduces gloss, whilst adding to opacity and lowering cost (cheaper than TiO2). That's something of an oversimplification because there are other and cheaper ways, depending on intended applications. Things like automotive paints tend not to be in demand in other than gloss, few people want a matt car! Although, I've seen it done...
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Ah... exactly the same as most photographic papers, then. Thanks!

Cheers,

R.
 
I wonder if there is a software that can use the scanner to scan a swatch of something and return the reflectivity of that swatch?
 
68degrees said:
I wonder if there is a software that can use the scanner to scan a swatch of something and return the reflectivity of that swatch?
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And if there is - do you have the means to calibrate it? You'll need two known-reflectance standards to do so. Seriously, without some big investments in kit you just cannot do this with anything approaching accuracy. Reflectance isn't a simple thing like temperature. What angle are you measuring at? Specular-included or excluded? Not features to be found on a scanner - assuming you're talking about the domestic/office-type document scanner connected to a computer.
 
It's all perception, Test Match Special, Pennine Radio, The Chris Moyles Show, Infrared Sidewinders, Photographs, Disco Lights, X-rays, and treatment for prostrate cancer are all the same thing, same waves (or particles) ... we humans simply experience them differently .. It is just Perceptive

The OP is confusing The Perception of Colours in Combination with Absolute Colour Values we humans can see the former only machines see the latter.
 
wolves3012 said:
... What angle are you measuring at? Specular-included or excluded? Not features to be found on a scanner - assuming you're talking about the domestic/office-type document scanner connected to a computer.
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ya I thought there might be a software for my flatbed that knows all the angles and variables of my scanner and can calculate reflectance when it reads the surface. Just curious.
 
68degrees said:
...
Also if i were to make a gray card (which are for pussies and wimps), not that I ever would but IF i did, what instrument would I need to measure what percent reflectivity it is? No one has answered that either. I suuppose I could by trial and error arrive at the formula for the right mix of black and white paint to come up with 18% reflectivity on a given surface, with a given sheen, and a given brand.

Yes Im learning a lot not just about 18% gray, but also on how anal some people can actually be. What level of precision is required here? How scientific must this be? To my knowledge no lives or limbs are hanging in the balance to get this dead on balls 18.000000000000001% reflectivity....
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This has been an interesting and entertaining thread, let’s not let it become unpleasant. I think you have narrowed down your questions. This could be a nice research project for you to dig into - maybe do some experiments to satisfy your curiosity.

While the discussion has been interesting, it seems the lack of clear answers to the issues indicates they are not very relevant to actual photography. You may need to let it go unanswered here for now, and revisit it when you’ve found more satisfying info.

Regarding 18% reflectance as a practical matter, taking a meter reading from a grey card should show the same result as taking an incident reading with the same meter, and be likely to give you a useful exposure setting for the scene.
 
1. Paint the wall black.
2. Set up full-length (ceiling to floor) vertical, hanging, white window blinds.
3. Pull chain on blinds to taste.

Voila! You now have a 0% - 100% black/white wall.

:D
 
Doug said:
This has been an interesting and entertaining thread, let’s not let it become unpleasant. I think you have narrowed down your questions. This could be a nice research project for you to dig into - maybe do some experiments to satisfy your curiosity.

While the discussion has been interesting, it seems the lack of clear answers to the issues indicates they are not very relevant to actual photography. You may need to let it go unanswered here for now, and revisit it when you’ve found more satisfying info.

Regarding 18% reflectance as a practical matter, taking a meter reading from a grey card should show the same result as taking an incident reading with the same meter, and be likely to give you a useful exposure setting for the scene.
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Highlight: not necessarily. NO film speed criterion is tied to 18% grey. Nor should meters be calibrated to it if they follow ISO standards.

On the other hand, ANY exposure metering system can be made to work, so yes, there is no doubt you will get a 'useful exposure setting'. But neither approach (incident/grey card) is ideal for shooting negative film with subjects having a long subject brightness range, as they ignore shadows in which you may want texture and detail.

The ONLY way to be sure of full shadow detail is to meter the shadows directly, and then either use a shadow index or give about 3 stops less than the standard index on the meter indicates.

The simple truth, though, is that neg/pos photography is so flexible and forgiving that it covers up numerous errors. This is just as well for countless photographers who think they know what they're doing, but don't, or who are looking for a precision that does not and cannot exist.

Cheers,

R.
 
wolves3012 said:
Things like automotive paints tend not to be in demand in other than gloss, few people want a matt car! Although, I've seen it done...
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It's become something of a fashion. The first time I saw it, on some up-market tonka toy somewhere in the Alps I thought it quite clever, if your vehicle is going to be covered in mud and slush why not paint it that colour to start. No it seem to be favoured by the sort of people who sound systems outpower the engine.
 
Heres a beautiful photograph and a pretty good example of semi gloss paint on a car. Me likey!

BrianLASalleSemiGlossPaint01-vi.jpg
 
68degrees said:
Heres a beautiful photograph and a pretty good example of semi gloss paint on a car. Me likey!
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I can appreciate the effort that went into it and I admire the dedication. Personally, however, I think it's pig-ugly. No arguments invited, strictly personal opinion! I bet is shows fingerprints terribly too.

And I bet the stereo makes the lights go dimmer...
 
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