Attention: Fotogenic & Custom Curve Users

Chris Sweet said:

I agree with Man here about using in camera JPEG's for these
sorts of tests. One less thing to worry about when trying for
reproducable results. It would still be interesting to see the data
using Normal curve with +.5EV or +.3EV against PS4 or EV3 with + -
0EV.

Even though this thread got sidetracked discussing using all the
right variables it is still a very good idea.

Click to expand...

Chris,

Yes, in retrospect jpeg would have been simpler, but it does have disadvantages. Once the custom curve has been applied to a jpeg, as I understand it, the characteristics of that curve can not be retrieved. However, in raw with Nikon Capture the curve is attached to the raw via a tag which can be extracted from the file and be verified. In the final analysis, I used raw since that is what I always do.

I follow Michael Reichman's writings on the Luminous Landscape and he once complained that when he publishes a test, no matter what methodology he uses, he is always innundated with e-mails saying he should have done this or that. And he is a recognized expert! You have to be pretty thick skinned in this business.

Bill Janes

Heh heh... As I added though, using Nikon's RAW conversion w/ accurate WB and no PP should probably be fine also. Yeah, using JPEG has disadvantages, but depending on the exact thing you're testing for, those disadvantages might not matter. I suspect for the sole purpose of testing this exposure accuracy issue, JPEG should be fine. However, if you want to do more than merely that (and use the other stuff that the Imatest tests for, eg. sharpness, noise, etc.), then yeah, you'll definitely want RAW. Just have to make sure you use a good, normalized approach, if you want to draw any real conclusions from the results.

And yeah, I'm sure it's definitely a tough thing to be in the shoes of MR, Phil and other reviewers who actually put in due diligence in their work. But then again, that's why there's a real market for this kind of stuff. And yes, I do very much appreciate all the hard work that they do -- and yours as well of course -- even if I might offer my own dollar's worth of unsolicited criticism from time to time.

And yes, thanks again, Bill. BTW, you did know I was just joking w/ the "measurebator" remark in my very first reply to this thread, right?

Very kind regards,

Man

Bill Janes said:

Chris Sweet said:

I agree with Man here about using in camera JPEG's for these
sorts of tests. One less thing to worry about when trying for
reproducable results. It would still be interesting to see the data
using Normal curve with +.5EV or +.3EV against PS4 or EV3 with + -
0EV.

Even though this thread got sidetracked discussing using all the
right variables it is still a very good idea.

Click to expand...

Chris,

Yes, in retrospect jpeg would have been simpler, but it does have
disadvantages. Once the custom curve has been applied to a jpeg, as
I understand it, the characteristics of that curve can not be
retrieved. However, in raw with Nikon Capture the curve is attached
to the raw via a tag which can be extracted from the file and be
verified. In the final analysis, I used raw since that is what I
always do.

I follow Michael Reichman's writings on the Luminous Landscape and
he once complained that when he publishes a test, no matter what
methodology he uses, he is always innundated with e-mails saying he
should have done this or that. And he is a recognized expert! You
have to be pretty thick skinned in this business.

Bill Janes

Click to expand...

--



Just another amateur learning to paint w/ 'the light of the world.' (John 8:12)
Motto for the season: 'Cameras are for making photos, not war...'
See my profile for more + some basic photog resources.
As usual, YMMV + caveat emptor.
Contact me at [email protected]
Indulge my fancies at http://www.pbase.com/mandnwong

Man-Fai Wong said:

Doh! I've been doing it all wrong all this time. I've been
exposing for people, things and places all this time, instead of a
gray card. No wonder my photos suck! ;-)

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that's a good one

Man-Fai Wong said:

Bill Janes said:

Now I understand. I redid my analysis exposing for +0.5EV for
Nikon's normal curve and 0EV for PS4. It does work as advertised.

Click to expand...

Ok, now that you finally understand that. I think it's my turn to
be confused -- or maybe just complicate things for you again.

I haven't dug too deeply into the sRGB articles (and controversies)
-- and don't think I have the time and expertise to fully
understand them -- but it seems to me that your test results (and
premise) goes against the grain of the various folks who argue that
the pixel level is non-linear, including Norman Koren himself. In
particular, the various sources you quoted, including NK and the
W3C site, provide a formula for sRGB that suggests pixel level for
18% gray should be 117.6 as you concluded in the first post that
started this sub-thread. But yet, your latest revised results
suggest it should be 127.5 assuming the D70 needs that +.5EV.

BTW, didn't you say at some point that you did get close to 117
w/out any compensation?

Seems to me that the problem remains, and we are back to square 1
here.

Click to expand...

The repeat test did not reproduce my original results as well as I would have liked, and I think I know at least part of the reason. To test the P&S curve, I needed a half stop increment in exposure, so I set the camera custom setting 9 for half stop increments and took a reading of the gray card and used manual exposure. The gray card reading was 1/15 sec at f/5.6, so I used this as the base exposure. In this mode, exposure would be rounded to the nearest half stop--I should have taken a reading in aperture priority mode. The actual shutter speed then would have been exactly what was needed without any rounding. Also in the new test I was working with IS0 200 and daylight. This shouldn't make a difference, but who knows!

Another way to check the calibration of the camera according to ANSI standards is to determine the characteristic curve as recommended by Fotogenic and Ansel Adams (by the way, I'm told Adam's beloved Weston meter was calibrated for 18%).

http://fotogenetic.dearingfilm.com/custom_tone_curves.html

I did this for my D70 using Fotogenics method and the results are posted

http://bjanes.smugmug.com/gallery/383257/2/15370963

A characteristic curve as done for film has a log scale for both axes. The x-axis is already log because f/stops are log. If you want to compare to film, you have to plot the pixel value as log also, but the linear y axis is easier to work with.

http://bjanes.smugmug.com/gallery/383257/2/15370964

To get the pixel reading for 0 EV exposure compensation, just read it from the graph. In this case it is approximately 113 pixels. This is very close to the predicted level of 117. By this test, my D70 is calibrated to ANSI standards very accurately.

http://www.bythom.com/graycards.htm

I was using AdobeRGB here, but for this pixel value there is very little difference between AdobeRGB and sRGB as demonstrated by a mode conversion (AdobeRGB to sRGB) in Photoshop iin 16 bit mode or the equation given by Nolt, who seems to very knowledgable (if somewhat conentious). If you are out there Nolt, please comment.

http://forums.dpreview.com/forums/read.asp?forum=1034&message=11966090

This curve is very easy for anyone with a gray card to construct, and I would encourage others to repeat it with their own cameras. According to Thoms's e-book, there is a plus/minus half stop tolerance in manufacturing standards but in his experience with dozens of Nikon bodies he has rarely seen any deviation.

For a masterful analysis of the Canon EOS D1 Mark II characteristic curve in both linear (raw) mode and converted 16 bit TIFF file with comparisons to Fujichrome Velvia and Kodak Royal Gold 200 see Roger Clark's site below. Roger is a PhD from MIT and works with NASA images as well as being a talented photographer and is very well qualified for such an analysis. He frequents the rec.photo.digital usenet group. Do a Google group search for him to get the opinions of a real expert.

http://clarkvision.com/imagedetail/dynamicrange2/
--
Bill Janes

Bill Janes said:

For a masterful analysis of the Canon EOS D1 Mark II characteristic
curve in both linear (raw) mode and converted 16 bit TIFF file with
comparisons to Fujichrome Velvia and Kodak Royal Gold 200 see Roger
Clark's site below. Roger is a PhD from MIT and works with NASA
images as well as being a talented photographer and is very well
qualified for such an analysis. He frequents the rec.photo.digital
usenet group. Do a Google group search for him to get the opinions
of a real expert.

Click to expand...

Using Polaroid SprintScan 4000 . He must be kidding.

Bill Janes said:

http://clarkvision.com/imagedetail/dynamicrange2/
--
Bill Janes

Click to expand...

Nolt,

Your reply is true to form. If you look at Roger's web site he has compared the SprintScan 4000 to high end drum scans and is well aware of the SprintScans limitations.

I have a SprintScan and it is a very good scanner. It doesn't have the dynamic range of the newer scanners but it gives very good images. Since the EOS 1Ds Mark II, surpasses 35mm (yes I know Roger was using the 1D Mark II), who is going to buy a new scanner unless they need to digitize their archive of 35mm?

I admit I am an amateur and am probably less qualified than you, but I don't know what your resume is. Can you match Roger's. Please post your qualifications.

http://clarkvision.com/rnc/

nolt said:

nolt said:

For a masterful analysis of the Canon EOS D1 Mark II characteristic
curve in both linear (raw) mode and converted 16 bit TIFF file with
comparisons to Fujichrome Velvia and Kodak Royal Gold 200 see Roger
Clark's site below. Roger is a PhD from MIT and works with NASA
images as well as being a talented photographer and is very well
qualified for such an analysis. He frequents the rec.photo.digital
usenet group. Do a Google group search for him to get the opinions
of a real expert.

Click to expand...

Using Polaroid SprintScan 4000 . He must be kidding.

nolt said:

http://clarkvision.com/imagedetail/dynamicrange2/
--
Bill Janes

Click to expand...

Click to expand...

Bill Janes said:

Nolt,

Your reply is true to form. If you look at Roger's web site he has
compared the SprintScan 4000 to high end drum scans and is well
aware of the SprintScans limitations.

I have a SprintScan and it is a very good scanner. It doesn't have
the dynamic range of the newer scanners but it gives very good
images. Since the EOS 1Ds Mark II, surpasses 35mm (yes I know Roger
was using the 1D Mark II), who is going to buy a new scanner unless
they need to digitize their archive of 35mm?

Click to expand...

I do not doubt that SS4000 is a good scanner; it's just not the proper tool to make DR analysis.

Densitometer - at the very least - should be used. SS4000 will not do justice to Velvia. Even PMT-based scanners sometimes have troubles with Velvia. Negative film was reversed with bluish tint, which indicates improper mask subtraction. Evaluation of scanner-induced noise - where is it?

Bill Janes said:

I admit I am an amateur and am probably less qualified than you,
but I don't know what your resume is. Can you match Roger's. Please
post your qualifications.

Click to expand...

Classified

Bill Janes said:

http://clarkvision.com/rnc/

nolt said:

Bill Janes said:

For a masterful analysis of the Canon EOS D1 Mark II characteristic
curve in both linear (raw) mode and converted 16 bit TIFF file with
comparisons to Fujichrome Velvia and Kodak Royal Gold 200 see Roger
Clark's site below. Roger is a PhD from MIT and works with NASA
images as well as being a talented photographer and is very well
qualified for such an analysis. He frequents the rec.photo.digital
usenet group. Do a Google group search for him to get the opinions
of a real expert.

Click to expand...

Using Polaroid SprintScan 4000 . He must be kidding.

Bill Janes said:

http://clarkvision.com/imagedetail/dynamicrange2/
--
Bill Janes

Click to expand...

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--

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