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View Full Version : Blue rather then dark purple.



jason51873
01-04-2009, 01:08 AM
I don't know if its just my camera, but when filming very deep purple neon or LED lit things it comes out blue! I just don't get it!

Here is a sample clip - at the end of the video there is a fountain that looks bright blue - but its actually a very deep purple.

http://vimeo.com/2462375
Look at the video at 1min 5sec in. that's the fountain.

I have tried all types of white balance settings, shutter speeds, iris, even different modes, and scene files - still looks blue :(

Broken camera? or broken user?

Thanks in advance for any help!

Thomas Lew
01-04-2009, 10:58 AM
Very strange.... I'm no help here but I'm very curious as to waht other people have to say.

ilauzirika
01-04-2009, 11:14 AM
It may be that the camera can't resolve the wavelenght of the purple light, it has also happened to me with UV lights and other purple light, but I'm not an expert in that field so we'll have to wait till someone that knows chimes in.

smelni
01-04-2009, 11:26 AM
the gamuts of cameras (color space) have a short cutoff of purples so many purples simple cannot be rendered properly - this is why experienced set designers and product designers will avoid purple since when shot digitally this issue comes up

smelni
01-04-2009, 11:28 AM
for more info see the chart below - it may not be the right gamut but you can see how many color spaces have a hard line at purples.

http://en.wikipedia.org/wiki/File:Colorspace.png

pd17
01-04-2009, 01:20 PM
Same thing on my camera . I shot something that had a purple color and it came out blue . Seems to be the way that the HMC 150 reproduces purple . Would be interesting to see if there are any settings that can adjust that .

Dave

Thomas Lew
01-04-2009, 01:39 PM
so digital video has a hard time with purple... any other colors to be wary of?

studio1972
01-04-2009, 01:48 PM
I had a similar problem with purple a while ago on my XM2 (Pal GL2). I guess it makes sense that it's a problem as Smelni described, which I hadn't realised until now TBH.

smelni
01-04-2009, 02:10 PM
take a look at a gamut pic for your camera - in other words if you camera is RGB then look at an RGB gamut and you will see what colors lie outside of it - those colors will not be rendered properly and will translate to something else.

JonathanS
01-05-2009, 09:40 AM
Red laser pointers are pretty bad for most cameras - the wavelength comes right where the response curve is starting to tail off. Green laser pointer spots show up much more vividly. This used to be a horrid problem with old tube studio cameras, but still seems to be an issue with CCDs. I don't know what CMOS cameras are like.

Incidentally, if you're ever doing a presentation that's to be filmed, make your slides light text on a dark background so they don't burn out / you don't disappear into backlit mud, as well as investing in a green laser pointer.

Er... I've gone a bit off-topic, haven't I?

jason51873
01-06-2009, 11:56 PM
Thanks a lot for all the comments. I'm glad its not just me! I guess there really is'nt much I can do about it cept ( stay away from that color ) hahah

Thanks for the help guys!

Humanoid Typhoon
01-07-2009, 12:42 AM
And here I was going MAD trying to match my Canon XH-A1's LCD to what I was seeing in real life via presets. Purples and really deep pinks I could never lock down! Now I know why. Great info :).

strangways
01-07-2009, 09:52 PM
Silicon based sensors, whether CCD or CMOS, are just not very sensitive to the ultraviolet end of the spectrum, which means they hardly see violet, and most RGB gamuts don't bother including it.

Purple, which is a different color than violet, is in between red and blue. It has no wavelength on its own - it is a combination of red and blue, or red and violet - which sensors can't see, so all violet and some purple shades are out. Also, I have a suspicion that having Red/Green/Blue sensors, or a bayer filter, makes it that much harder to resolve colors falling in between those primaries.

This problem was discovered a few years ago with digital still cameras, and a company marketed a controversial Photoshop plugin claiming to correct it.

More info:
Wikipedia Violet (http://en.wikipedia.org/wiki/Violet_(color))
Wikipedia Purple (http://en.wikipedia.org/wiki/Purple)

Violet is 380-450nm. This chart shows how silicon sensors lack sensitivity to it:
http://www.ph.tn.tudelft.nl/Courses/FIP/images/fip139.gif
http://www.fullspectrumrgb.com/images/problemglance.jpg