Creating a good workspace for Color Correction

Rodrigo Silvestri · April 20, 2008

Hi. I am an Argentinian film student and, with luck, a future Director of Photography.

I am one of those who think that you have to know all the tools first, and to let the creativity do its work. I like to have the whole control of the images of my projects, and now I am starting to learn about color correction.

I changed my Mac some months ago, and am getting really used to Final Cut Studio. I started using Color a month ago, doing tests and things like that, which led me to start reading about color grading.

Something that I read among all the things, and that called my attention, was that some colorists have a white card with a pure-white light that they can turn on to use as a reference.

I am really interested in buying a good 6500ºK light and a white card, but would want to know where to buy it.

Some months ago I was studying by myself all about high CRI fluorescent light, and concluded that even a 99CRI light can be greenish, because the CRI doesn't directly mean the color, but the amount of "color ranges" that the light emits.

So I know that what I need is a good pure-white light. And I even think that it doesn't need to be high CRI, because I am only interested in reproducing a 6500ºK white with it, and not other colors. Is this correct?

Can anyone recommend me a brand or place to look for a light like this?

Can LED light be an option?

I could use an incandescent light with filters, but I would need to change it often because their color temp. decreases with time.

Thank you,

Rodrigo

April 21, 2008

Something that I read among all the things, and that called my attention, was that some colorists have a white card with a pure-white light that they can turn on to use as a reference.
I am really interested in buying a good 6500ºK light and a white card, but would want to know where to buy it.

White cards are too intense, they leave an after-image. What you want is an 18% grey reference. For video / desktop grading, this should be a grey surround, i.e. a card or wall behind your monitor painted neutral grey and illuminated with a daylight bulb. For a DI suite using projection, this isn't very practical, so I simply use an 18% grey still image on screen when I need it.

You can buy GTI Standard Gray Neutral 8 Vinyl Latex Paint from B&H and other places to paint a wall or card yourself (it's expensive). There are lots of daylight bulbs of different types and most of them will be fine for general use. You can spend several times more to get true D65 lights if you want to be careful, but I think it's a case of diminishing returns for most (although we spent it for our studio and I'm not sorry).

Michael Nash · April 21, 2008

so I simply use an 18% grey still image on screen when I need it.

I'm not a professional colorist, but this is what I use at home for general-purpose image work. I surround the frame with 50% luminance gray. It provides not only a neutral color reference, but a neutral luminance reference as well.

Paul Bruening · April 22, 2008

LEDs are spiked frequency lights. I have the same concern about flos but most here aren't concerned about them and feel the CRI is high enough. Jack James prefers a dark room. He says that SMPTE standard is 6500K. But where are you going to get a full spectrum room light at 6500K. By the time you throw in LUTs and DAZzing... well. Maybe if enough people offer their opinion here, you can get a common practice consensus.

Adrian Sierkowski · April 22, 2008

I would be more concerned, personally, about the color calibration of the monitor you're working with than the wall colors. I'm not expert, but I do know that PC/MAC have different gammas, and FCP Color, as far as I know, does not recalibrate your monitor to show "true," colors.

Something else to look into perhaps?

Michael Nash · April 22, 2008

FCP Color, as far as I know, does not recalibrate your monitor to show "true," colors.

It probably goes without saying that you need to view your work on the same type of display that you'll be delivering for. In other words, you really need to output to an NTSC CRT to see how the work will look on that type of display.

As I understand it FCP does apply gamma correction that simulates a CRT. But you do still need to set up your monitor properly to get it as close to "accurate" as possible, even for home color-correction.

Rodrigo Silvestri · April 22, 2008

LEDs are spiked frequency lights. I have the same concern about flos but most here aren't concerned about them and feel the CRI is high enough...........

In my first post I said that I don't need a high CRI light. CRI is only involved when you want to reproduce colors (like if I want my red jacket to appear with an intense red). That is because CRI means the amount of color peaks that the light has. To generate a pure white, I only need red, green and blue, each one in its exact measures.

Michael and Adrian: I already read about monitor calibration... Might make a new thread about that later.

Thanks,

Rodrigo

Paul Bruening · April 22, 2008

I'm probably being too anal about frequency spiking, Yet, I feel I should mention that those spikes don't fall evenly in terms of RGB. They're generally selected to fool the human eye and only enough to work and still keep lamp manufacturing costs to a minimum. They will, definitely, alter the accurate representation of colors on a reference chart. How much and in what colors is the question. Each source will do different things to those colors. It may not really matter enough to be a concern for you. I wish I had some quantitative data on the matter. Given the importance of the topic to colorists, there seems to be little opinion on the matter.

It could be easier to build a light box sandwiched with 3200K tungsten lamp, frosted glass, color correcting gel to 6500K, then chip chart transparency. Then you can set the monitor to 6500K and work in the dark.

As far as I'm aware of tungsten and halogen lamps are the only forms that deliver an unspiked, full spectrum source. Even HMI's spike. Unless someone has a better idea, gelling a conventional lamp may be it while remaining cost effective. More lower watt lamps in a broader lamp house will decrease gel degradation. Gels are cheap enough to just cut fresh ones regularly.

Here's a link to a D65 explanation:

http://en.wikipedia.org/wiki/D65

Rodrigo Silvestri · April 22, 2008

It could be easier to build a light box sandwiched with 3200K tungsten lamp, frosted glass, color correcting gel to 6500K, then chip chart transparency. Then you can set the monitor to 6500K and work in the dark.
http://en.wikipedia.org/wiki/D65

Tungsten lamps are very susceptible to time and voltage. Their color temperature decreases with use.

Also (I don't know if this happens in the US, but I think it does), I live in Argentina, and the voltage here is not always the same. I mean... it should be 220V, but sometimes it's 218 or 225, and that changes the color temperature too.

I think that fluorescents don't change the color over time, but their intensity lowers.

Thanks again,

Rodrigo

Paul Bruening · April 22, 2008

This is a little complicated, Rodrigo. Would a Minolta color meter give you a dependable measure to make adjustments by?

They're still a little pricey, even on Ebay. They're not much good with spiked lights but would do fine on tungstens. I haven't priced voltage regulators.

Rodrigo Silvestri · April 23, 2008

I'm not -and will not soon be- a professional colorist.

I'm just trying to see which is the best way of achieving a good workspace for semiprofessional color correction. What I mean, is that I won't spend lots of money on equipment to have it all perfect, but I am going to do some things that put me near that.

I thought a way of calibrating my light, please tell me if it's useful or if it has some flaws.

I have a DV camera (Panasonic GS500 3CCD). I can connect it to the computer and view a live vectorscope. So I thought that I can put the camera's balance in Daylight, then turn on my 6500K 80CRI CFL and point the camera to the wall. I get a slight green peak (8% I think), and I use my Lee Filters catalogue to mix filters and see what I need to correct. In this case, a 1/4 Minus Green works OK (need to go and buy it, because the catalogue is too small).

I could use this for monitor calibration now, but I think that I should talk about it in another topic, so I made