Spikes in profiles

Is they a simple explaination why this Prophoto RGB Wide Gamut profile has such a sharp spike in the blue?

The Wireframe object is the Adobe 1998 profile.

members.optusnet.com.au/~theyan/ … oPhoto.jpg

OT…

iccview.de/index_eng.htm

Might give you some ideas for using ColorThink code to create an interactive web display for online use. Worth some investigation perhaps.

At 6:04 PM -0700 8/17/05, Yani wrote:

Is they a simple explaination why this Prophoto RGB Wide Gamut profile has such a sharp spike in the blue?

The Wireframe object is the Adobe 1998 profile.

http://members.optusnet.com.au/~theyan/chromix/ProPhoto.jpg

Yes, it’s fairly simple. ProPhoto RGB’s blue is not a “real” color.

As RGB spaces are defined by their 3 color coordinates, they are subject to the limitations of a "triangular"shape - as seen when graphing in 2-D in Yxy. So, the only way to make a bigger space is to move the RG or B colors “out”. The ProPhoto RGB bluse is so far out that while it can be stored in a number, it doesn’t actually correspond to a perceivable color. This is OK in most cases as production colors will never be in the range of 0,0,255 but when we draw the gamut of the profile we calculate all the way out to these extreme edges.

The graphing in ColorThink is done in Lab which, in the area of blues in question, shows real colors for real numbers. The ProPhoto blue, as it gets converted to Lab, gets pushed in and that is why it looks odd in a Lab graph.

OK so that might not have been the simplest answer after all…

http://www.iccview.de/index_eng.htm

Might give you some ideas for using ColorThink code to create an interactive web display for online use. Worth some investigation perhaps.

yes, we have been looking at a few alternatives. One of them is QuicktimeVR movies as well… we’ll let you know when we come up with something.

Regards,

Steve


o Steve Upton CHROMiX www.chromix.com
o (hueman) 866.CHROMiX


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Another answer would be that ProPhoto is spiked like that so it can incorporate the whole gamut of color slide film, such as Ektachrome, which has a larger gamut in those deeper blue areas, right?

Steve, would it be fair to say it’s a real color, we just can’t see it?

[Gamut of sRGB,eye and nature)