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Subject: Re: ACR Calibration



OK folks, here goes.

I am not an expert in color science or chip manufacturing, but my background (40 years in the computer industry) should allow me to express some opinions.

Unit to unit differences should be minimal. When you pay $3000 or more for a camera you should expect quality control. Maybe not true for a $150 point and shoot camera.

If someone wants to help prove this, please contact me offline. What we need is controlled CC shots from different units of the same model camera. Nikon, Fuji, or Canon will do. Studio flash properly exposed would be the preference. Daylight can change too fast.

The spectral accuracy at one nanometer increments would be 300 or 400 data points for each of four channels. Most of the color science stuff uses interpolation from 5 nm tables (60 data points). This would not bloat the metadata. This would improve color accuracy by significant orders of magnitude. And we still have the existing tools and options to achieve any aesthetic look we desire.

I asked Fuji about this at Imaging USA. The answer came today. Sorry Charlie. They claim it is trade secret information. Nonsense! This data has been published for pro film for years. Frequently, itís included in the box. If it were publicly published, it wouldnít even have to be in the metadata. Some sensor makers (Dalsa for one) already publish it, but it is in graphic form rather than table form. An independent body with the proper equipment (very expensive) could instrument and report this for all the popular sensors.

The ISO metadata tags do exist, but no one is using the spectral information tags or the real white balance tags. DNG does accommodate something similar. I prefer the open ISO solution over any vendor owned solution. I have an article on some standards research on my web site.

It is impossible to design any sensor that realistically matches CIE XYZ or CIE RGB. These are derived color matching functions based on human psychological responses (psychophysics), not a sampling of physical devices.

Shooting RAW puts the darkroom on your desktop. We need the same tools we had with the wet processes. There are several good tools for camera profiling, but they depend on rendered images under repeatable conditions. Phase One seems to me to offer the best solution for true raw calibration so far. But they donít support my cameras so I havenít actually tried their tools.

IMHO, the answer is open standards. ISO TIFF/EP is the horse I want to ride. There needs to be a standards compliance reporting or enforcement body in place. The ISO does neither. Until the affected users understand what true open standards can deliver, chaos shall reign.

Unfortunately, OpenRAW is focused on all encompassing documentation instead of the real solution, standards compliance. Surveys and mass mailings to the vendors seem to be the order of the day. This will never fly.

Yes, there seems to be a bit of voodoo mixed in with true science. Sometimes the voodoo becomes group think.

Cheers, Rags :-)
www.rags-int-inc.com

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