Digital BW, The Print

Hi Paul,

What you are calling metamerism is actually color constancy. That disclaimer aside, a measuring device won't pick this up as it has a single, full spectrum light source. A camera will pick it up, but it's necessary to photograph a good, spectrally neutral gray ramp along with the image, in order to have a known set of neutrals to go withe the unknown variables. Cameras measure in RGB which is less than ideal, but you can get approximate Labvalues out of them in Photoshop, after normalizing each image under your assorted light sources to have the same luminance for white and black patches, and color balanced to the gray ramp. 

Since the normalization process noted above, and the target noted above, are exact matches to the SpyderCheckr, I might as well admit that, and just say: shoot your sample print, dead flat, in the same plane as the Checkr, and light both as evenly as possible. The follow the normalization directions for the Chreckr in Lifhtroom or Adobe Camera Raw, without cropping, and you can then export to Photoshop, where the eye dropper tool will supply Lab values for your ink gray ramps. 

If you don't have a SpyderCheckr, send me an email off list and we will work on remedying that. 

C. D. Tobie
Global Product Technology Mngr.
Imaging Color Solutions
Datacolor.com
CDTobie@...

On Apr 17, 2012, at 1:26 PM, "Paul" <roark.paul@...> wrote:

> Metamerism has become an un-expectedly significant issue in my experimenting with glossy neutral printing. I never had to worry about it with the 100% carbon printing approaches. 
> 
> In addition to the dyes for cards, one significant goal for me is to develop an appropriate glossy medium that can hang near my Eboni-6 matte prints and have them both look good under varying lighting conditions. 
> 
> The energy-efficient CF and LED lights are major contributors to the problems I'm having reaching this goal. 
> 
> While I knew the dyes reacted relatively poorly to fluorescent lights, the extent of this metamerism with the older fluorescent lights (CRI 75) surprised me. They can have a major green/blue/cyan shift. 
> 
> I have also been surprised by the extent of the metamerism I see in prints made with neutralized carbon plus LC & LM. There seems to be a significant reddish shift under the new LED lights. Of course, the more color in the print, the greater the problem seems to be for B&W.
> 
> Is there an easy way to objectively measure and describe the degree of metamerism?
> 
> Paul
> www.PaulRoark.com 
> 
> 


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