Hypothetical question

[Kettering_Jeremy]

I was asked a hypothetical question at work yesterday regarding black and white photographs.
The question is, is it possible to derive colour information from a black and white photograph exposed on black and white film? For the sake of argument it is assumed that no coloured filters were used in the original exposure.
Depending on the photograph it may well be possible to set maximum values for white and black, and some colours may be known (green grass, blue sky), but not the exact hue. Let us say for example that one wants to determine the colour of a shirt worn by someone in the photograph, where there is green grass, blue sky, and pure white and pure black. Is this possible – even in theory?
My gut reaction is that it is not possible. That feeling is based on the assumption that different colours could produce the exact same shade of grey, and hence could not be differentiated.
If it is theoretically possible to determine colours in this way, does anyone know of an example where this has been used?

[MickLL]

Not in my opinion or experience.

As you say different colours can (and do) produce the identical shade of grey on a mono film.

Having said that I'm sure that some clever fellow will say I'm wrong

BTW this answer is based on what you wrote not some other situation.

MickLL

[El_Sid]

Wiki on colorization...

[daft_biker]

Wiki on colorization...

Colourisation surely? Clicky.

I know I can't spell but the yank spelling makes me cringe

I suspect it's easier to work out the colour of things based on other references than just the shade of grey in the photograph. You could get different shades of grey in different lighting, with different film, with different processing and with the age of the photograph so I suspect it's impossible to do with any level of accuracy. Logic might be able to deduce a shortlist of possibilities but I suspect that would be about it.

[pilliwinks]

Many years ago this came up in Victor Blackman's Cameravaria. You're going to have to get someone to search the archives if you want to find the article, but it was probably 1963-67.

He'd met someone (can't recall whom) who claimed that the different wavelengths of light affected the grains in film differently, and that it was possible to reconstitute the colours - using some unrevealed process. VB did put him to the test, and got back a colour print with amazingly a yellow cast in the foreground caused by an out of image yellow object that VB knew was there but the other fellow didn't.

I find this as hard to believe as VB did, but it's the nearest I've ever come to hearing that it's possible.

[zx9]

Many years ago this came up in Victor Blackman's Cameravaria. You're going to have to get someone to search the archives if you want to find the article, but it was probably 1963-67.

He'd met someone (can't recall whom) who claimed that the different wavelengths of light affected the grains in film differently, and that it was possible to reconstitute the colours - using some unrevealed process. VB did put him to the test, and got back a colour print with amazingly a yellow cast in the foreground caused by an out of image yellow object that VB knew was there but the other fellow didn't.

I find this as hard to believe as VB did, but it's the nearest I've ever come to hearing that it's possible.

The 1st April issue perchance?

[MickLL]

Wiki on colorization...

Interesting but not relevant to the question.

MickLL

[pilliwinks]

The 1st April issue perchance?

As I said, I can't recall the issue - but after over 40 years I was pleased I recalled as much as I did. If it was an April issue, it will be a simple matter for an archivist to find it. But I had the impression at the time that he was completely serious.

[Kettering_Jeremy]

Many thanks for your answers so far.

The colorisation thing is interesting, but not quite what I was getting at.

Victor Blackman was writing for AP when I first started reading it back in the 1970s, but I don't recall that article. (Mind you I don't recall a lot of things these days)

Ayyway - thanks once again.