Ad
Ad
Ad
Pages: « 1 2 3 [4]   Bottom of Page
Print
Author Topic: CS3 ability to open jpegs in Raw  (Read 21466 times)
bjanes
Sr. Member
****
Offline Offline

Posts: 2756



« Reply #60 on: May 25, 2007, 07:10:02 PM »
ReplyReply

Quote
WAY OFF.  Here’s another one from Thomas Knoll: "Actually, to create a camera filter set that is "perfect", it is not required to exactly the match the human cone responses (or the XYZ responses). All that is required is the filter responses be some linear combination of the human cone responses. If that is the case, then a simple 3 by 3 matrix can be used in software to recover the exact XYZ values.”

--
[a href=\"index.php?act=findpost&pid=119650\"][{POST_SNAPBACK}][/a]

Peter,

Thanks for entering the thread. Yes, I remember that answer by Mr. Knoll, which was in response to a question that I had posted. I had presumed that the digital camera filters would get best results when they matched the response of the human cones, but fortunately this stipulation is not needed and camera makers have some latitude in the filters. Unfortunately, he added that current digital camera filters are not linear and so we don't get perfect matches.

From my work with DCRaw, I saw that the source code contains this note: Thanks to Adobe for providing these excellent CAM -> XYZ matrices! The coefficients in the matrix are listed for various camera models. I presume that when one calibrates ACR with the Fors script or manually by Bruce Fraser's method, one is refining the values of these coefficients which describe the characteristics of the camera filters.

Bill
Logged
PeterLange
Guest
« Reply #61 on: May 27, 2007, 02:35:48 PM »
ReplyReply

Quote
Hello Bill,

Yes, I remember this discussion very well: it was Oct. 2005 when the introduction of Simon Tindemann's script challenged Adobe folks - for good reason as I have to add: http://www.xs4all.nl/%7etindeman/raw/color_reproduction.html

With best holiday-greetings from a sunny Greek island,
Peter

--
Logged
eronald
Sr. Member
****
Online Online

Posts: 3870



WWW
« Reply #62 on: May 27, 2007, 02:45:51 PM »
ReplyReply

Quote
Here's more fun with the potential hurt me buttons discussed.
[a href=\"index.php?act=findpost&pid=118895\"][{POST_SNAPBACK}][/a]

Andrew,

I think you need a trademark on the term.


Edmund
Logged

Edmund Ronald, Ph.D. 
jbrembat
Full Member
***
Offline Offline

Posts: 177


« Reply #63 on: May 27, 2007, 03:35:28 PM »
ReplyReply

Quote
The CIE XY space is not perceptually uniform, and your article states "correlated color temperature is the color temperature of the point on the blackbody locus that is closest in appearance (chromaticity-wise) to the chromaticity of interest. Technically, this means the point on the blackbody locus nearest the point representing the chromaticity of interest when the blackbody locus is plotted not on the CIE-xy chromaticity diagram but rather on the CIE-uv space chromaticity diagram"

Therefore, for this type of plotting you should be using a perceptually uniform space such as CIE-uv or CIE LAB, not CIE-XY. If you want to find the shortest distance from a point to a line, you drop a perpendicular from the point to the line. With CIE-xy the lines of correlated color temperature are not perpendicular to the Planckian locus, but  with a perceptually uniform space, I would think that they should be. If you want to nit pick, you should have your ducks lined up in order.

A tint of -2 in the magenta direction is very close to the Planckian locus. Of course, magenta is not on the Planckian locus, which runs in the yellow-blue direction. Really, what point are you trying to make?
[a href=\"index.php?act=findpost&pid=119535\"][{POST_SNAPBACK}][/a]

CIE_Lab cannot be used as white reference is required.
The orthogonal lines are computed on CIE-uv space and then converted to CIE-xy space for plotting. That was done to save the same dyagram reference.
I confirm that your photo lights are far from Planckian locus.
I confirm that using a graycard you can correct images illuminated by non-blackbody sources.

Jacopo
Logged
bjanes
Sr. Member
****
Offline Offline

Posts: 2756



« Reply #64 on: May 27, 2007, 08:53:13 PM »
ReplyReply

Quote
I confirm that your photo lights are far from Planckian locus.
I confirm that using a graycard you can correct images illuminated by non-blackbody sources.

Jacopo
[a href=\"index.php?act=findpost&pid=119879\"][{POST_SNAPBACK}][/a]

Thus far I have seen nothing from you to prove anything. What evidence do you have that my lamps are far from the Planckian locus?
Logged
jbrembat
Full Member
***
Offline Offline

Posts: 177


« Reply #65 on: May 28, 2007, 07:09:03 AM »
ReplyReply

Quote
Thus far I have seen nothing from you to prove anything. What evidence do you have that my lamps are far from the Planckian locus?
[a href=\"index.php?act=findpost&pid=119914\"][{POST_SNAPBACK}][/a]

You wrote:
Quote
You completed the exercise by showing that a decent white balance was possible from the shot with the wrong color balance.

My correctin was  deltauv = -0.02 .... far from Planckian locus.
Logged
bjanes
Sr. Member
****
Offline Offline

Posts: 2756



« Reply #66 on: May 28, 2007, 07:39:44 AM »
ReplyReply

Quote
You wrote:
My correctin was  deltauv = -0.02 .... far from Planckian locus.
[{POST_SNAPBACK}][/a]


Without any description of how you derived that Delta uv value, your assertion about the Planckian locus is meaningless. Furthermore a Delta uv of -0.02 is pretty small. See [a href=\"http://www.kenrockwell.com/tech/dslr-comparison/lcds-2006/index.htm]Rockwell[/url].

Since your posts are undocumented assertions not backed up with any explanation or data, they are not worth any further response.

Bill
« Last Edit: May 28, 2007, 07:41:41 AM by bjanes » Logged
jbrembat
Full Member
***
Offline Offline

Posts: 177


« Reply #67 on: May 28, 2007, 08:37:16 AM »
ReplyReply

Quote
Without any description of how you derived that Delta uv value, your assertion about the Planckian locus is meaningless. Furthermore a Delta uv of -0.02 is pretty small. See Rockwell.

Since your posts are undocumented assertions not backed up with any explanation or data, they are not worth any further response.

Bill
[a href=\"index.php?act=findpost&pid=119968\"][{POST_SNAPBACK}][/a]
I do not wait for any response from you. I write for the forum users.

Anyone can judges.

Just to clarify for readers: the same deltauv on low color temperature produces more distance from Planckian locus. Rockwell reference mentions high color temperature.

Jacopo
Logged
bjanes
Sr. Member
****
Offline Offline

Posts: 2756



« Reply #68 on: May 28, 2007, 09:47:59 AM »
ReplyReply

Quote
The illumination is not far from the Planckian locus as shown in this screen capture in ACR. I preset the white balance with a reading from a white card.

[attachment=2553:attachment]

Bill
[{POST_SNAPBACK}][/a]

For those who are interested in a scientific analysis of the color quality of various lamps, [a href=\"http://www.slrcamerainfo.com/article.php?filename=Lighting-and-Color-]John Beale[/url] has posted an informative article.

The ACR temperature slider moves along the Planckian locus and the tint slider adjusts for deviations from the Planckian locus along the magenta-green axis. Light sources that closely approximate black body radiators have a small tint correction. If the light source has a discontinuous spectrum, the temperature and tint sliders may not be able to produce accurate color matching, as shown by the Imatest plots.
Logged
Pages: « 1 2 3 [4]   Top of Page
Print
Jump to:  

Ad
Ad
Ad