Re: Primer on photographic exposure, etc.
Dear Wayne, Can you please describe how you got raw data from cameras, and how the data is normalised? What procedure was used while taking the shots? What lens was used on the camera, and what are the spectral properties of the lens? -- Best regards, Iliah Borg
On May 16, 2013, at 7:28 AM, Iliah Borg <iliah.i.borg@gmail.com> wrote:
Can you please describe how you got raw data from cameras, and how the data is normalised? What procedure was used while taking the shots? What lens was used on the camera, and what are the spectral properties of the lens?
I'd love to know this, too -- and, Iliah, on the same subject...any chance you could offer a few more details on your monochromator setup? I'm especially interested in both the hardware configuration (integrating sphere?) as well as how you (presumably) know the XYZ value of the samples you're photographing. Are you measuring the monochromator output with a spectrophotometer? If so, how does the low resolution of the spectrophotometer interact with the narrow spectral characteristic of the monochromator? (If it's not obvious, I've never worked with such a device, so pointers to introductory materials would also be welcome.) It seems to me that it would be very helpful for reproduction work to get a series of measurements with a monochromator (with camera lens) and to add them to the measurement data (Argyll's .ti3 file) of every chart measurement (using the same lens). It would alleviate all the concerns of a limited total chart gamut -- though you'd sill want as large a gamut as possible with as many samples as possible on your chart. Thanks, b&
Dear Ben, On May 16, 2013, at 11:26 AM, Ben Goren wrote:
I'm especially interested in both the hardware configuration (integrating sphere?) as well as how you (presumably) know the XYZ value of the samples you're photographing. Are you measuring the monochromator output with a spectrophotometer?
Integrating sphere, a diod to measure intensity, spectrophotometer is not needed if a monochromator is calibrated. -- Best regards, Iliah Borg
On May 16, 2013, at 8:46 AM, Iliah Borg <iliah.i.borg@gmail.com> wrote:
a diod to measure intensity,
Ah -- as described here, I assume: http://fraden.brandeis.edu/courses/phys39/Thermal%20Control/EMANT/Applicatio...
spectrophotometer is not needed if a monochromator is calibrated.
-- and, presumably, if the photodiode is also calibrated. It seems to me that one should be able to confirm the calibration of the various instruments by measuring them against each other -- or, at least, get some idea of the level of disagreement and the margin for error. I'm guessing the handheld photographic light meter should probably also be included in the calibration mix. Thanks for the information! I think I know enough to take it from here for building my own setup -- or, at least, for figuring out how much it'll cost and whether or not it's worth the money for me.... Do you happen to have any personal recommendations for vendors for this type of equipment? Cheers, b&
The data was tak en from various web sites. I am out of town for a few days and don't have the references here. I suspect that the Canon data was taken without a lens, but I am not 100% sure. The data did not come from Canon, but from others interested in the response with and without the built-in infrared filter . The film data is from Kodak data sheets. I would not propose that this paper be taken as definitive measurements of a particular camera or a particular batch of film. but rather as indication of the general effects of camera filter shapes and an indication of how to go about the characterization . I will try to recall the process for you , although I do not have the supporting material here: In some cases the published curves were plotted as quantum efficiency, and if I recall correctly, I adjusted those curves to represent spectral response, or else found spectral response curves. The spreadsheets I used for calculations used the spectral reflectance of the 24 patches (except that black and four gray patches were not included). These were multiplied by the spectral content of daylight (I need to review if I used D65 or D50). These products were further multiplied by the CIE functions for the eye or the color channel responses for the camera. The camera responses were also calculated for a perfect D65 (D50?) spectrum, and the resulting R,G,B values used to normalize the output for white. A linear matrix was then calculated for the camera to give best fit to the eyeball colors of the patches. Finally, using this matrix, the reported chromaticities of the gaussian spectra and single-wavelength spectral colors were calculated. How much variation there is from unit to unit of a particular model of DSLR, I do not know, but all of a particular model should be similar in gross characteristics such as approximate spectral width, the presence or absence of bumps in the spectral response of each channel, etc. I developed the calculations, but I have to depend on others' measurements. ----- Original Message ----- From: "Iliah Borg" <iliah.i.borg@gmail.com> To: "Wayne Bretl" <waynebretl@comcast.net> Cc: "Lars Borg" <borg@adobe.com>, colorsync-users@lists.apple.com Sent: Thursday, May 16, 2013 9:28:11 AM Subject: Re: Primer on photographic exposure, etc. Dear Wayne, Can you please describe how you got raw data from cameras, and how the data is normalised? What procedure was used while taking the shots? What lens was used on the camera, and what are the spectral properties of the lens? -- Best regards, Iliah Borg
Dear Wayne, On May 16, 2013, at 9:34 PM, waynebretl@comcast.net wrote:
The data was taken from various web sites. I am out of town for a few days and don't have the references here. I suspect that the Canon data was taken without a lens, but I am not 100% sure. The data did not come from Canon, but from others interested in the response with and without the built-in infrared filter.
One of the sites that published data with and without IR filters is maxmax.com but they used out of camera JPEGs to get the data. -- Best regards, Iliah Borg
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Ben Goren
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Iliah Borg
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waynebretl＠comcast.net