View Full Version : RGB nubers for warming filters

Gregory von Liebig
16-Aug-2001, 21:51
Hi all,

Could someone tell me the RGB numbers, for warming filters, or a source where I can get them. I want to do an experiment in PhotoShop, but no one seems to know .

Thank, you for your help.


Ellis Vener
16-Aug-2001, 22:32
it is a combination of red + yellow values, the ratio depends on the strength of the filter.

Pete Andrews
17-Aug-2001, 07:13
There no fixed relationship between real world colours and digital image RGB values. It depends on the target 'colour space' used, and the gamma interpretation used during the digitisation process. (i.e. The 'colour profile' of the capture device)

Subject brightness starts out linear, and can be anything up to many thousands to one. This all has to be compressed into 256 non-linear steps per colour of a digital image, and this inevitably involves comromises and colour mismatches.A typical monitor can show about a 600:1 brightness range, and a good printout maybe half of that.I'm trying to give you some idea here of the difficulty of maintaining a fixed colour temperature shift through all these transfer functions and over all possible output gamuts and spaces.

Using the L*a*b* 'colour space' in Photoshop should go some way toward standardising a colour, but fixed RGB numbers, no chance!

John O'Connell
17-Aug-2001, 08:17
The L*A*B space might get you closer than RGB, but it's still a Euclidean color space and probably won't do a good job replicating what goes on with your eye or with the film.

If you're already in Photoshop, just adjust the color to preference and forget about what the filter would have done.

john g
17-Aug-2001, 12:35
Try shooting a white piece of paper in daylight with a neutral trans. film like EPN. Or use your favorite film so you get the effect you are used to. Process then compare the filter and transparency on a light table if the are close you are in bussiness. When I say close keep in mind each film deals with color differently if it is close it would be the same color addition that you are used to. Next scan it in with a film scanner. If your system is color calibrated you now have a solid color image that you can load in as a mask or with your eye dropper tool get the RGB numbers.

Gregory von Liebig
17-Aug-2001, 15:07
Thank All for your responses. I have to explain myself. The reason I need the RGB numbers for the warming filters is that I want to experiment with color overlays in PhotoShop. I do not have problem correcting color casts, I just want to mimic the filter effects. If anyone has the numbers for the Tiffen 812, and the standard 81B, 81C, 81D, 81EF and the 85 warming filters I would be very grateful. The scanning option does not work for me as I do not have access to a film scanner, and a Drum Scan would be too expensive.