Color meter and colour charts

[shutterboy]

I am trying to understand the utility of hand held colour meters and colour charts (like macbeth) for accurate colour representation. I understand that films, unlike digital sensors have a "baked" white balance in it and is pretty tolerant towards coloured light. So, where does a hand held colour meter like a Sekonic C-500 fit into the workflow? Also, how does a colour chart fit in?

Thanks

 

[chriscrawfordphoto]

They're actually more useful for film than for digital. With digital, you can adjust the white balance after you shoot (if you shot a RAW file rather than a JPEG). With film, the film is made for one color temp (5500K) and if you shoot under light that is not that color temp, the colors in the photo will be off. The color meter tells you what filters to use on the lens to get the color perfect. This is for slide film mainly, since color neg film can be color corrected in the printing process. So, for slide film, the color meter is useful, for digital or color neg, its not important.

 

[bernard_L]

With film, the film is made for one color temp (5500K) and if you shoot under light that is not that color temp, the colors in the photo will be off.

This statement, as it stands is not correct.

This is for slide film mainly, since color neg film can be color corrected in the printing process.

That is correct. More precisely, negative film can be corrected as long as it's not close to underexposure: under, say a 2700K illuminant, blue light is so scarce that the blue part of the image would hit the toe of the curve and could not be corrected. Bottom line: in case of low-Tc ("red") ambient light, with negative film, give generous exposure. And, use one frame to picture a photographic gray card, that will help you in post-processing to establish objectively the color balance without guesswork. Much cheaper than a colorimeter and more effective.

 

[Mr Bill]

Hi, I mostly concur with the other two posters.

Main use for a color meter seems to be to determine what camera filters to use with a color transparency film. You could also use it for color neg films if you just want to be closer to the film's native color balance. For example, if you want to use a normal (daylight balanced) color neg film under tungsten lighting, this is quite a stretch, so a filter might be called for. You could use a color meter for recs, although it seems more sensible (cheaper) to just look up the filters in a color conversion table.

Another use would be if you wanted to filter your flash to match ambient lighting.

To me, the biggest problem for color meters are with newer lighting, like the energy-efficient fluorescents or LED lights. I don't think the conventional meters are much good with these, because of the odd spectral-energy distributions. (I've compared Minolta and Gossen color meters vs spectrophotometer readings of energy-efficient fluorescents, and the color meters didn't do very well.)

Regarding the Macbeth ColorChecker, this was designed in the late 1970s as a reference tool for testing color reproduction (C.S. McCamy et al published a descriptive paper on it). It roughly mimics the spectral makeup of a few things, light and dark human skin included, along with a number of test colors. It was sized specifically to allow densitometer readings on a 35mm film frame, in addition to visual use.

You could use the chart to test different films or light sources. Without the chart, you might have to collect several human models, a few pieces of fruit, and a half-dozen samples of colored fabric. Every other person who tests has completely different test objects. The chart gives a standard reference object, and has become something of a de facto standard in the photo industry. Anyway, there are a number of possible uses, although an individual photographer might not find it very useful.

 

[AgX]

This is for slide film mainly, since color neg film can be color corrected in the printing process. So, for slide film, the color meter is useful, for digital or color neg, its not important.

-) filtering in the printing stage for wrong exposure light-temperature has to be based on lowest densities. Thus loosing density range of the film.

-) filtering at the exposure stage will yield a negative that can be standard-filtered for the mask and paper. One does not need a grey card or other reference in the image nor has to rely on averaging image colour.


Seen that a transparency in its slide appearance is looked at in the dark, thus with no colour references, correct colour balance of a print is even more important than that of a slide.

 

[Xmas]

If you are using a studio with tungsten light you need to be using a tungsten balanced film. Or you use a balance filter and sacrifice film speed or post process with reduced dynamic range. Burn red channel or no detail in blue shadows.

Meters and colours wont be good under lots of other light conditions. Avoid non continuous sources.

If you don't use a grey card you won't necessarily have a happy customer, even then you can have perception problems when they compare the print and fabric in sunlight, girls keep their wedding dresses... until the next.

If you are going to project in dark room maybe but back projection in subdued light maybe not. Some people still use slides for prints!

Colour can be difficult.

 

[DREW WILEY]

I don't trust many grey cards to be accurate, but the MacBeath Chart, along with the grey patches on it, is a very wise acquisition to testing any kind of color film. Forget all the digi talk about white balance etc and get back to the basics. For any particular film you want to look up the mfg tech sheet for that specific film, to not what color temp it was balanced for. All your testing should be done under that particular standard. I happen to use a Minolta color temp meter. The quality of the light can be balanced either by filters over the light source (studio) or by filters over the lens (outdoors). A nice soft white light works best on daylight films. Some films like Ektar can be particularly sensitive to color temp errors, but in principle it applies to any of them. Wacko spectrums like fluorescent and CFL lighting will give you the biggest headaches. But outdoors things get fairly predictable. For example, I always carry an 81A warming filter for bluish overcast skies, an 81C for deep shade under deep blue northlight or high altitude, plus an appropriate skylight filter for minor corrections.
But you don't really know exactly what you need until you do some actual testing, along with representative readings with a color temp meter.

 

[DREW WILEY]

Bill - I'm a bit amazed just how thoughtfully developed the MacBeath chart has been. You've got your primaries and direct secondaries. When
a "standard" neg or chrome is made from these, and then the print itself properly balanced, these respective color patches will all "sing" with
just about the same intensity. Different films have different kinds of bias, of course, but this one particular feature will allow you to properly
address that fact as well as things like tuning your colorhead to the specific paper batch. Then you've got a true neutral gray scale, which itself will come out neutral over its full range if properly exposed then printed. Then you've got various patches equivalent to skintones and
common off-colors. Just putting a bunch of paint chips together and photographing them won't yield this kind of precise accuracy. The thought that went into these charts in the first place becomes more apparent the most advanced one becomes as a color printer. Yeah,
they're a bit pricey. But there's a reason for that.

 

[Mr Bill]

Bill - I'm a bit amazed just how thoughtfully developed the MacBeath chart has been.

Yes, it was a first-class effort by people who knew what they were doing.

I never understood why Macbeth or X-rite, etc., never continued to make the original SPSE paper available. But I see now that there is an on-line copy per a link from wikipedia. http://www.cis.rit.edu/~cnspci/references/mccamy1976.pdf

Anyone who thinks the chart is just some casual collection of colors would probably find this to be an eye-opener.

 

[DREW WILEY]

The printing inks have to be very specially chosen and then fully studied under a variety of lighting and spectrophotometer plots to make something like this. Every notice how when you pick up a paint chip in a paint store then order the paint, they frequently never really match?
That's because the printing ink and paint pigments are two totally different things, and will respond to light sources differently. The MacBeath
chart is designed to see color the way your film is meant to. That's quite a trick. I've been involved with various spectrophotmeter designs, and my wife worked in biotech with a super-secret one for DNA trade secret applications that was kept in a room that literally had a bank vault door in front of it, closed after hours. ... more to protect the proprietary software than the physical machine itself, which XRite provided. But it has actually taken me a few decades to learn the full potential of that basic MacBeath chart. Every color patch on there has a specific reason for being there, and has been precisely balanced in relation to all the other specific colors. Once you understand that, it
becomes an extremely valuable tool not only for choosing films and basic color temp problems, but even more as an expressway to calibrate
your printing paper efficiently. I seem to finally understand what that damn chart itself is thinking about the film or paper, and visa versa.
It's a way more sophisticated tool than a simple gray card.

 

[AgX]

I don't trust many grey cards to be accurate,...

There is a guy in Germany who devoted most of his life to designing and making grey- and colour-cards.

(All those Photokina vistors here will know him.)


http://www.fotowand.com/

 

[DREW WILEY]

There's quite a trick to it, and it's very commendable if anyone can mass produce these. I did it once with paint pigment and a serious spectophotmeter. You can't just use black and white to create gray. There is no such thing as a pure black pigment. You have to balance all
kinds of things very carefully. I managed to make a paint that was almost perfectly 18% gray clear across the visible spectrum, and one step into both IR and UV. By comparison, not even one of the commercially made gray cards I purchased at that time was even close. They didn't even match within the same brand. Certain things coming onto the market more recently seem to be better. The spectrophotometers themselves were calibrated to a specific ceramic tile, which doesn't fade and can be easily cleaned.

 

[JWMster]

Speaking strictly as an amateur returning to film and picking up an old thread resurrected in lieu of repeating the content, I want to be sure I'm reading this and understanding this rightly: So long as we get in the right ballpark of exposure (half stop or less) and color temp, we can color correct our negatives in post processing... whether with software or filtering on an enlarger. More to the point, the use of LED's and newer light sources tends to outdate the old (Minolta) affordable color temp meters. And likely if we're not trying to precisely match a corporate color (e.g. Tide XK box) it's not something we're going to need. If this is close to right, then sweating the difference between 3400 and 3200 isn't a big deal with film. Digital is pretty much a snap in post, but I'm going to otherwise not worry about this all that much and run with my eyes and experience on slide film. Shoot a color checker or gray card if you want to get more precise, and work with that just like in digital I guess.... if you want. So the price of used Minolta color meters at $100 or so probably reflects fair price in terms of actual utility (i.e. not much).

 

[WilmarcoImaging]

Your film statements are close to right, using your phrase, for non-critical (ie no paying client) applications. I would add emphasis that exposure needs to be sufficient for the film to be correctable. Sufficient exposure is higher for, as an example, color negative film exposed with tungsten lighting.

 

[DREW WILEY]

Films differ, as well as our personal expectations. For example, many color neg films, esp amateur ones, are engineered for a relatively wide degree of error, but there's always some compromise tied to that. But a higher contrast, more evenly shattered neg film like Ektar has far less margin for error. Chromes are actually easier because you can just slap em on a light box and see what you did.