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There is a very free script available that will do exactly what you describe.
Google "Thomas Fors" and download his ACR script.
Mr. Fors has done the digital capture community a great service with his work on this script.
Thanks Rick. This looks very interesting.
At present I do not have a Macbeth chart.
Before I go ahead on this can you (or anyone else who's used the script) tell me whether the results are better than those obtained simply by using the white balance tool in ACR on a Kodak grey card contained within the image.
This is the method I use at the moment for critical projects - and it works just fine. I'd like to know the advantages of Thomas Fors method however.
Thanks in advance.
chrisjbirchall: it is not instead of using the WB tool, it is as well as.
I had a problem with my Pentax - the ACR generic calibration for the Pentax resulted in poor greens with my camera. I assume my camera has a significantly different response from the camera used by Adobe. In effect, greens (especially grass) needed the equivalent of about 10 to 15 "hue" in Photoshop's Hue & Saturation. (Even after using the WB tool in ACR).
The software that came with the Pentax gave better greens. (About the only way it was better than ACR!)
I used Thomas Fors' script, and now have new defaults for the Pentax in the Calibrate tab. (I saved them as camera defaults). ACR applies these automatically for ALL Raw photographs I take with my Pentax. So my system now treats a Pentax differently from the way your system would. (Strangely, the script did not results in just a change to the green hue in the Calibrate tab, but a much more complicated set of values).
This hasn't changed the way I set WB. (I use a grey in the scene if there is one, then fine tune subjectively). I don't run the script for each session, and certainly not for each photograph! It simply means that I get better looking grass. (And the settings get written to the DNG file as XMP metadata by ACR 3.1). In fact, I ran the script for 4 different illuminants, and it is the daylight one that is the new camera default, but the others are saved in case I want to apply them.
I carry both a Kodak grey card and a GretagMacbeth Color Checker in my car all the time. Nowadays I tend to use the GretagMacbeth, (2nd square along the bottom row), rather than the Kodak, if I want to photograph a reference grey during a session. I'll probably stop carrying the Kodak around.
Barry. Thanks for the insight.
I can see now that this script will come in handy when I (eventually) get around to trading in my S2s. I'm pleased with the way the Fuji renders colour - particularly skin tone (80% of our work is portraiture).
However the Fuji is not a fast camera (the S3 even less so) and the build is not very substantial. A couple of people I know have moved - one to Canon the other to Nikon - and whilst pleased with the cameras they both mourn the loss of the Fuji's colour rendition.
This script looks just what is needed to ease the transition.
Well, what about the people who live in far away places, like for instance Macedonia, who can't use the script cause they can't buy a Greta. card.
Can anyone post the results?
The results are only good for the specific camera that shot the test. Even two Canon 20D's will be different from one another.
If you purchased a digital camera, you can surely purchase a MacBeth Color Checker card from the same company, yes?
Perhaps you can get together with several other photographers and purchase one card to share. Good luck!
To tell the truth I've never been happy with the Gretag Macbeth Color Checker method of setting up ACR. Too often I've gotten faster and better results eye-balling the calibration settings. My mixed camera pool of seven is thankfully all Nikon, but each camera differs as much as each model.
For the record I've never been able to make a usable custom camera profile either. Custom camera profile aficionado Ethan Hansen has said elsewhere that the standard GM Color Checker has too few patches to work effectively.
>Custom camera profile aficionado Ethan Hansen has said elsewhere that the standard GM Color Checker has too few patches to work effectively.
that's why GM offers the $300 GMB107 color checker for digital cameras. :-)
the GM method helps me set a ballpark for a camera/lens combination. after that it's all relative.
> that's why GM offers the $300 GMB107 color checker
> for digital cameras. :)
IIRC Tom Fors' script only works on the 24 patch Gretag Macbeth Color Checker.
the 300$ patch thing from greatg or others do not work:
ther is , for ex., in gretag one a black plastik swatch which will reflect light always differently, depeneding of the angel of attack of your light source.
so the calibration process will calculate the wrong thing . always !!
that just for starters.
the 24 patch is actually more accurate.
even that script mentioned above is nothing professional:
first you have to use a photospectrometer to meassure the patches from your gretag card, in order to even have an accurate goal. ( the cd that comes with the chart is not accurate enough)
and only then the profilmaker from greatg will know where the colors have to end up.
and something like this would be easy to make by the adobe people..!!
The reference data values for the 24-patch color checker used in Tom Fors script were provided by me. They are averaged from spectral measurements from approximately 50 different physical samples of the Color Checker. The standard deviation is quite small, and is generally below the granularity that Photoshop's integer-based implementation of Lab allows. I've run experiments where I compared the results of the script with manual adjustments that take measurements of the specific ColorChecker being shot as their aim point, and I can tell you with a high degree of confidence that unless your Color Checker has been subjected to very unusual wear and tear, the reference data in the script is more than adequate.
The purpose of the script is quite limited. Its sole purpose is to adjust the R, G, and B primaries of the built-in Camera Raw matrix profiles to account for unit-to-unit variation in the cameras. (Depositing RGB filters a few microns thick onto a chip is an inherently variable process, and is responsible for much of the unit-to-unit variation.)
A single, static camera profile is, in my experience, useless for just about anything except the image of the target used to build the profile, and other images taken under identical lighting conditions. I certainly get more accurate color from Camera Raw than I do from a custom camera profile built using ProfileMaker Pro and the ColorChecker SG.
There's a fundamental mismatch between ICC profiling technology and digital capture. ICC colorimetry is output-referred. We need scene-referred colorimetry. The Camera Raw solution to this fundamental issue is, in my view, brilliant. For each supported camera, Camera Raw contains two matrix RGB profiles, one built under Illuminant A, the other under D65. (The profiles were built by Thomas Knoll using his own proprietary profiling tools, which I suspect are better than anything on the market if the CMYK profiles bundled with Photoshop are any indication.) The white balance controls interpolate between (and extrapolate beyond) these two profiles.
The two huge benefits of this approach are
1.) It works under all lighting conditions, which a single ICC profile does not.
2.) It preserves accurate relative hue and saturation while allowing me to impose my own tonality, which is a great deal more useful to most photographers than a single LUT-based profile that compresses the scene dynamic range into the output dynamic range the same way for all images, whether of a polar bear in the snow or a black cat in a coal cellar.
There are many raw converters that allow you to use a custom camera profile built by ProfileMaker or its competitors. If that's really what you want, I suggest you use one of those. But this is an approach that would cripple Camera Raw, and I would argue strenuously against it. I doubt that Thomas would go for it anyway, for all the aforementioned reasons.
every theorie needs to first have a strong foundation.
i am sure you agree with that fact.
although i am astonished to hear that your meassuremenets of different gretag cards were almost identical, i have to agree that raw 3.1 is a fabolous tool.
but one just must "start" with a much as possible perfect foundation.
and thats always numbers meassured by machines.
so if i were to start a shoot with my sinar 54m or the 54h and shoot such a chart
have its software give me an in camera profile for each lighting situation, then my results are excellent.
this is experience.
if i start with a canon 1ds markII file and with raw (and i am including the monor quality issue) i do find myself in 2 situations.
the sinarback is always brilliant in colors, even in shades.
a constant that is unbeatable.
the canon files are never as great as the sinar files, so therefor to start with an accurate colorprofile is nothing less than an absolute necessaty.
if i were to be able to "first" force the colors to the 24 patches, an "then" play around with raw 3.1, then that would be the only way to achieve the max.
and believe you me, as a fashionphotographer working this planet all over, and on top of it i am swiss, there cannot be a compromise.
i have found myself tryning to match this patch thing for hours with these sliders and still was not happy.
so i started talking to the gretag people in switzerland and the binuscan people.
and as a serious consumer need to say, if raw would have this script implemented, then only it would make the max out of most files out there.
sorry was in a rush, made alot of grammatical errors.....
am going to dinner with a superbeautiful girl.....
Building a profile for each image is somewhat practical, albeit time-consuming, for photographers shooting under controlled lighting in the studio. It's a total non-starter for photojournalism, editorial stock, sports, and a great many other situations.
Part of the difference you see between the Canon and Sinar files may be due to the profile, but I suspect a great deal more is due to the camera. You typically get what you pay for.
I've worked extensively with the photographers at the National Gallery in Washington DC, which uses the Sinar for all in-house photography, and even with a custom profile for every image, we still encounter the issue of camera metamerism, and quite often the tonality imposed by the profile is not the tonality we need, but when we impose our own tonality we get color shifts. A custom profile is not a panacea, it's simply a tool that's more useful in some situations than others.
Forcing the colors to the 24 patches is exactly what Tom Fors' script does. The 24-patch color checker is extremely stable, and manufactured under stringent conditions. The spectral formulation has changed twice in its history, but the resulting tristimulus values match across generations to within the margin of intrument variation on mid-range spectrophotometers like the Gretag SPM 100 and Spectrolino. If you left one out in the sun for a year, it would probably fade some, but who does that?
When you factor in the minimum granularity of the adjustments, which are dictated by 12-bit or 14-bit camera RGB, the variation between color checker samples is smaller than the smallest adjustments you can make in the software.
How about a "collected wisdom" or "advanced FAQ" book that Something as
an adjunct to "Color Management" and "PS ACR" that would collect some of
your newsgroup responses and things like your experience at the National
Gallery, for people who might wan to know more.
It's on my to-do list, but it has a lot of company!
One of the major issues with profiling digital cameras is virtually every product treats a camera as if it were a scanner. Thats kind of silly.
The ICC has a white paper (I hate that term) which discusses some of the reasons why this is the case.
>For each supported camera, Camera Raw contains two matrix RGB profiles, one built under Illuminant A, the other under D65. (The profiles were built by Thomas Knoll using his own proprietary profiling tools, which I suspect are better than anything on the market if the CMYK profiles bundled with Photoshop are any indication.) The white balance controls interpolate between (and extrapolate beyond) these two profiles.
if I want to compensate an image shot at sunset, how is an illuminant A response going to help?
There is no need for "scene-referred" colorimetry or "output referred" colorimetry, there is just a need for measuring the linear response colorimetry of the capture ccd. I don't believe that the ACR internal profiles are any different than linear gamma, matrix based ICC profiles.
And I should be able to select that profile based on image editing needs, it should not be selected for me based on a colortemp slider. A different colorresponse due to different lighting conditions is in fact completely unrelated to colortemp.
So, why aren't we able to build linear, matix-based ICC profiles to replace the internal profiles of ACR?
Or, if it has to be simplified, why not add a "Response Type" popup with choice of "Daylight", "Incandescent", "Fluorescent" etc and then have the colortemp slider interpolate between profiles that actually are relevant. I doubt that Thomas is willing to build that many profiles for each camera, but hey, that's why I asked: why aren't we able to build linear matix-based ICC profiles to replace the internal profiles of ACR?
This topic is well timed, at least for me. My 24-patch Macbeth Color Checker just arrived. I ordered it after reading your discussion of the Calibrate tab in the latest edition of your Camera RAW book.
(Shameless sucking up message: That book is terrific. Thanks very much for the hard work that went into it. That book and your Color Management book are written in clear, accessible English, and they took away so much of the confusion regarding digital photography that had me going in circles before. I have recommended both to others. Thanks.)
As I understand your book and this discussion, all that I am doing with Tom Forss script is tweaking the manner in which ACR uses its two built-in profiles (one under D65 illumination and the other under tungsten). Is that correct? I am not building a profile at all, just telling ACR how to account for variances in my own camera.
I do have one question regarding running the script. Once I shoot the Color Checker and run the Fors script and put the numbers from the run into the Calibrate tab, am I finished? Your book recommends using the Fors script as an easy way to calibrate ACR for my camera, but you also explain how to run the process manually, for those who are so inclined. In reading your book, however, I was not entirely sure where the instructions for manual calibration began and ended. I THINK that all I need to do is run the Fors script and plug in the numbers, so that I dont need to follow the detailed instructions regarding tonal adjustments, bringing down the Brightness and Contrast values, and trying to match the target image with the reference image downloaded from colorremedies.com., etc. That means that I really dont need to use the reference image from colorremedies.com. Could you just confirm my understanding? If I dont have to mess with trying to match colors between the reference and target, either by eyeball or number, that would be great. (If this is all self-evident in the book and I am just misreading it, just call me an idiot and tell me to read the book again.)
I have another question (I lied about having just one). Do I need to run the script and create different calibration settings for different lighting situations (daylight, tungsten, flash, etc.)? You say this on page 99, but I was not sure whether this applied to running the Fors script or doing the manual procedure, or both.
Finally, do you recommend using the cameras on board meter for exposing the Color Checker or a separate hand held meter, or does it matter? (I have an old Gossen LunaPro SBC meter which has served me quite well for over 25 years, and would be happy to use it for this.)
Thanks for your guidance.
1.) The two main sources of unit-to-unit variation in cameras are the chip sensitivity, and the filter densities. You can compensate for the chip sensitivity variations by determining the real ISO speed of the camera, on which more later. The script, and the Calibrate tab it drives, are designed to account for variations in filter density. They move the R, G, and B primaries in XYZ space, so they're just moving the corners of the built-in profiles ot ore accurately match your specific camera.
2.) When you run the script, all you need to do is to plug the numbers into the Calibrate tab (and, ideally, save them as a settings subset). You don't need the reference image, and you don't need to adjust anything. You seem quite intelligent, and since you were smart enough to buy my book, I certainly won't call you an idiot, but you may want to re-read the relevant section....
3.) I find I can get by happily with 1 calibrate setting for daylight and another for tungsten. Tungsten needs to be special-cased because of the double whammy of a blue-starved light source and relatively inefficient blue filters. Strobes generally have a pretty full spectrum and behave much as daylight does.
4.) Gossen-type meters are essentially useless for digital. They assume a film-like tonal response curve, and measure average scene luminance. DSLR's don't have that film-like TRC, so you won't get good results from that type of meter. I use the built-in meter, spot-metering for the highlights (In overrange situations, I spot-meter for where I want the highlight to be.) First, though, you have to determine the real chip ISO sensitivityI've seen nominal ISO 100 be anything from ISO 75 to ISO 150, and there are plenty of cameras I haven't seen.
I used a Minolta Spotmeter F I borrowed from Jeff Schewe to determine that my Kodak DCS 460's ISO 100 was really ISO 80, my Canon 300D's ISO 100 was actually ISO 125, and my Canon 20D's ISO 100 really was pretty damn close to ISO 100, as follows.
Meter a bright highlight with the meter set for ISO 100, and take a shot with those settings. Repeat at different ISO settings on the meter. Then look at the images and see which one captures the highlights as hot but not blown with no Exposure adjustment in the raw converter. That's the real ISO of the camera, so if it's different from the nominal ISO you can dial in the appropriate exposure compensation on the camera. (My 300D is set permanently at -1/3 stop, though I'd prefer -1/4 but it's not an option on that camera.)
You'll really have to ask Thomas this question, but I suspect he's justifiably skeptical of the ability of current commercial profiling tools to estimate accurately the real R, G, and B camera primaries based on the capture of current profiling targets, all of which have tiny gamuts compared to the real world.
Thank you very much for taking the time to post such a detailed response. It cleared things up well. I hope that it will be of use to others, too.
Your comments regarding the Gossen meter were disappointing, but, I suppose, not surprising given the differences between film and digital. I have managed to get good results with it, but I have always been more of an intuitive, instinctual photographer than one who shoots by the numbers. (I would dodge and burn using my hands, push and pull film like crazy, speed development of select portions of prints using my fingers in the tray, and I always used meter readings as just a good starting point and went on instinct to select the final exposure.) That served me well with film, even chromes, but I am really learning all over again with digital.
What I appreciate most about your explanations is that they are allowing me to see where in digital capture I have the latitude to run a bit outside of the numbers. Exposing for the highlights and learning my cameras real ISO will be very helpful in this regard. I will get to work on the ISO issue, because I can see how important that will be.
I have been seriously working on digital capture for about a year now, and my images have progressively gotten worse. I take this as a good sign, however, because it means that I am weaning myself (sorrowful as though this might be) from my own film-based approach to image making. And, let me say that your books have been instrumental in making my pictures worse; in a good way, of course... All kidding aside, your explanations have been great. Thanks again.
Now, I will go back and re-read the calibration section of your ACR book (again).
Bruce, can you elaborate on your comment about Gossen? All of them?
I cannot understand that, given your capabilities for getting at the root of the matter and working out the details, you would summarily dismiss a brand as you did.
All meters are able to be calibrated. if nenecessary, filtration can be added for those who wish to do so. I don't expect you to do so, and certainly I can set down at a calibrated light source and proceed, but I am curious as to the reasons for your dismissal.
I'll jump in. . .it isn't a "brand issue" so much as it's a "type issue". Basically, reflected light or incident light meters are designed to measure light to expose FILM, with film's responce curve. This is what Bruce meant. He has nothing against Gossen or any meter brand. It's the issue that light metering for digital exposures is an entirely new problem.
A spot meter that can measure scene luminance is far more useful to digital exposure. First, it tells you whether or not the scene is inside or outside the dynamic range of the sensor and second, it can tell you what is the most critical textural white that a certain exposure will provide.
The old handheld or through the lens meters designed for use with film are really old tech. Arguably, a digital sensor itself can be a really high tech light meter if only the camera companies would design a method of getting useful feedback from it. . .
what about a GOSSEN light meter--like the old luna pro--that has a spot meter (lens) attachment? does anyone know if it measures the actual scene luminance or the reflected light? i'm not sure how a simple lens attachement can neutralize a response to film?
Response curve to what? Color?
I noticed he uses a Minolta spot, yours, Jeff,which is also old tech, AFAIK, but he said the Gossen was essentially useless. Also, are you all saying that digital is not panchromatic? I certainly understand that if there is significant deviation at parts of the spectrum, your meter will err accordingly.
I used Tech Pan for years, which has extended red sensitivity, to which I had to respond. I can tell you it was rather different than putting a red filter over the lens or the lightmeter and shooting say Panatomic-X. So I do understand what happens. But I also didn't trash the light meter. I didn't even need to filter it.
I use a Gossen LunaPro F with spot attachment, which had been (not lately, however) calibrated to a known, traceable light source. It had no particular problems at different parts of the spectrum, although if you want to split hairs, it was different than the older Gossen Luna Pro, which is a ***** at the hi-low crossover point. The Weston masters were still different. (But then, looking at the spectrum of several types of color film, one might wonder how any consistency can be obtained!)
They all were quite useful, and I used them interchangeably, settling on the Gossen "F", which I use to this day.
You got my curiosity way up, and since I have access to a Canon 20D, and the owner is also an engineer, we may take a shot at this, at least in general terms.
I notice, Bruce, you favor calibrating to the high value. I have always cal'ed to middle gray, or what is referred to as Zone 5. I can well understand metering for this, as blowing highlights in digital has greater consequences than in film (with Tech Pan I actually used highlight placement as a contrast control!), but I haven't seen that portion used as the reference for calibration. It shouldn't make any difference, so long as everyone is doing the same thing!
Right about the sensor being an adequate meter. It is a meter! It simply needs right numbering of the output, in the right units. :-)
I may actually regret jumping in this deep! Makes be feel that shooting film and scanning is still best for me. Things getting worse the more one learns does not exactly instill confidence.
The attachment is for reflected only on the Gossens.
As Jeff said, it's a type thing, not a brand thing.
Metering for Zone V was OK with film, because Zone V was squarely in the middle of film's tone curve.
DSLRs don't have that highlight compression, and Zone V is way down around 50 or so on a 0-255 scale. Fully half the data the camera captures is devoted to describing the brightest f-stop the camera can record at the selected exposure/ISO settings. If you underexpose, and hence fail to populate that range with captured data, you're only capturing half the tones the camera can record, and you'll be fighting posterization and banding when you try to redistribute the captured data across the whole tonal range.
You're always going to get better results with digital capture when you stretch the highlights, darkening the midtones and shadows, than you will by compressing the highlights and lightening the midtones and shadows, because the camera captures much more highlight detail than we can see, and much less shadow detail than we can see.
Within limits, digital raw give you a huge degree of latitude in where you place the midtone, but those limits are imposed by where you set the highlight point. Everything hangs off the highlights, so the key decision you need to make when exposing for digital capture is where you want to set your highlight point. That's why I spot-meter on the highlights.
The tone response of the sensor medium is the biggest and most confusing difference between film and digital. Film behaves approximately like eyeballs. Digital capture doesn't, not even vaguely. A useful exercise in trying to get your head around thisat least it helped me a lot, is to make a linear-gamma grayscale gradient, and watch what happens as you shove the bits around to try to make it approximately perceptually uniform.
Digital isn't panchromatic eitherit's way more sensitive to red and IR than it is to blue and UVbasically the opposite of filmbut that's a much smaller issue than the difference between a perceptually-weighted response and a linear one.
I assume when you say that digital is way more sensitive to red and IR it's the sensor output, before digitizing, to which you refer. The engineering battles must be interesting to deal with it!
As a person far more attuned to shadow placement than highlights, at least in the capture mode (You "place" the shadows, the highlights "fall") I find it disconcerting in the very least.
I keep forgetting the log/linear aspect of digital capture! Zone 5 would be about 50 idealized. Maybe as low as 32 as there is no baseline film base+fog issue to set the black point.
The more I think about it, the more I can see that you must start at the MSB and get that correct first, then work down. And, it makes no difference whether we are in an 8 or 16 bit environment. It still applies, for it is the dynamic range of the sensor which has to be handled correctly. As I recall, the same held true in digital audio. At least there, the mistakes would be painfully obvious!
Some of this also makes sense for scanning, although one actually makes visual decisions right from the get-go. No concerns over ISO, white point etc. And, I would imagine the linearity is much more controlled.
Thanks, Bruce and Jeff, for getting back so quickly!
Enjoy the holiday! :-)
that script did not work on cs2 (error messages etc etc, ) , and the support email to tom bounced back.
any good info how i can make it work?
also i wanted to ask you, if we could possibly have a phone conversation.
i have a couple of ideas and questions and statements, where i would really like to get your reaction on.
by the way here some of my work, in case you were curious:
and here some newer work on my europeans website:
here a test with the sinar 54m (studio shots) and the canon 1ds markII (outside shots)
203 east 7th street apt 4
new york, ny 10009
tel: 212 982 4445
The current script, which executes with no problems in CS2 on the three machines I have here, is at
I'm trying desparately to finish a book before leaving for three weeks in my homeland, Scotland, on July 22. We could probably talk sometime in September, but I simply have no spare bandwidth until then.
Yes. . .now you are getting it. It is the linear nature of digital sensors that completely changes the assumptions one makes about exposure from the standpoint of film responce experience.
It should also be noted that the "Zone System" is also pretty much out the window as well. The Zone System requires swings of contrast around a center point of Zone V. As you now realize, there is effectively, no Zone V with linear captures, not until to apply a gamma tone curve responce.
The camera companies have done a pretty good job of trying to make digital look like film-which is really not something I want. The cameras that are currently converted film caperas still need to go a long way to fully realizing the digital potential. For example, on Canon's at least, the histogram of a capture is not really useful as it doesn't really give any useful info on a raw capture, only the camera raw to sRGB conversion. The newer cameras DO allow you to view histograms by channel, but if you are shooting raw, the histogram is still make believe. At least with early cameras, Canon admitted that the highlight flashing option was intentionally set one full stop conservative-which lead to a _LOT_ of under exposures and noisey captures.
The camera companies need to come up with a far better way of displaying the results of a sensor capture and providing much better info regarding raw captures. An meters need to reflect the reailities of linear captures vs film TRC's.
Actually, re-getting it, Jeff! I wonder how many times, how many iterations I have to go through....<br /><br />In the engineering lab, I have no problems. I look at the data sheets, look at the results required and make it so. But as soon as the photographer's hat goes on...<br /><br />To be fair, the learning curve to transfer thinking from linear to log was equally difficult. Teaching the concepts of exposure with such a dense process was daunting. Especially when the numbers were sometimes exponents, like f stops, and sometimes linear, like shutter speeds. That still holds, and is a anachronism, IMO. Who really needs to know the ISO number? Not me. Slow, medium and fast is all I need from a digicam. Even those names are anachronisms! I got several rolls of film sitting in my camera case. They are not going anywhere!<G> So now, we shift gears in our heads.<br /><br />Because I am still wedded to film, I won't be giving up the filmic way of thinking yet, so I do have some practice time available.<br /><br />I completely agree with you about digicam methodology. I don't know what's to gain by the current thinking. Comfort? No way!<br /><br />BTW, it's not correct to think of the Zone System pivoting around Zone 5. Were that so, the shadow density would actually decrease with extended development, which is how contrast is controlled. It increases, so the pivot point is actually about Zone 1. With PS, you can obtain the effect to which you are referring by pinning the curve at 128 and pulling up on the curve beyond 128. The curve below 128 will now decrease in values. Pulling up on the upper curve does not duplicate extended development correctly, but only approximately. To mimic film development with Curves is a bit more tricky, but possible.
> it isn't a "brand issue" so much as it's a "type issue". Basically, reflected light or incident light meters are designed to measure light to expose FILM, with film's responce curve
I've had nothing but trouble with incident readings in daylight (serious underexposure) and I keep thinking...what, have I simply forgotten everything I knew years ago about making light-readings? It used to be like breathing in and breathing out! What's up with this, anyway?
Then again, when I take a flash-reading with the same meter that's giving me fits outdoors, the exposures (20D) are typically right on the money. Go figure...
Setting aside the notion of response differences (actually a calibration issue) I would first check the meter against a known, accurate reflected light meter, or if tour meter does both, against itself in both modes. Use an 18% card that's clean for the reflected reading.
The circuitry for flash is different than for continuous reading.
You did have the meter on continuous and not strobe, didn't you? ;-)
(Been there, done that!)
"BTW, it's not correct to think of the Zone System pivoting around Zone 5. Were that so, the shadow density would actually decrease with extended development, which is how contrast is controlled."
Ever do a D log H curve? :-) Base + Fog and the toe of the curve really doesn't change with development.
In point of fact, traditional reflected light metering is indeed based upon what later became Zone 5, it's called an 18% grey card. When read by a refelected light meter, this was supposed to place an 18% reflectance as a middle grey on a B&W neg (this was well before color materials).
+ and - processing only changed the slope of the resulting processed tone curve and had a greater effect above Zone 5 than below it. Lower exposure would develop out and not change much even with increased development. But density above middle grey (highlights) would rapidly increase in density with longer development. Hense the ability to alter the contrast of a B&W neg-which was made largely moot by variably contrast B&W papers, which alas, Kodak will no longer be making.
Ever read the book Photographic Sensitometry by Zakia and Todd? I had to, since they taught several of the classes I took at RIT. When Adams developed the Zone System, it was before panchomatic B&W films (they were mainly orthochromatic then) and there was little one could do to alter the contrast of printing papers. That's why he developed the variable contrast approach for negs, which he processed primarily by inspection.
Digital photography with it's linear capture is so foreign to that concept as to make traditional photography a roadblock to learning how to expose digital captures today. And meters based upon an 18% reflectance have less usefulness than spot meters that can measure scene luminance and allow you to determine the scene dynamic range. This will alow you to determine when the scene is within or outside of the dynamic range of the sensor.
You might be surprised at how many scenes are within the sensor's dynamic range. In those cases, increasing the exposure up to the point of near clipping will give a much more controlable and flexible result.
Oh, the curve function in Photoshop bears little or no relationship to tone responce curves in film. . .film had a toe and a shoulder with straight line portions that either increased in slope (more contrast) or decreased in slope, producing lower contrast. But the lines were generally straight except for the toe and the shoulder.
Boy, have we come a long way. . .
I have done many DlogH curves, and at one point, owned the Zakia /Todd book. No, the toe does not change much with increased development, but it does change. And yes the changes beyond middle gray (Zone 5; 18% gray)are greater than below, but again, it does change. Film speed does change as a function of development, and film speed is based (variously over the years) on just how the film comes out of the toe, it is inescapable that the curves pivot about the toe, roughly speaking, that is. The curves not only pivot there, the toe can increase in F+F value thereby showing a vertical displacement on the plot. If you take individual plots of a particular film over differing development changes, and overlay the curves such that the toes merge (roughly!), you will see that the slope of the curve does rise from the toe. I have lots of graphs in storage if you would like to see them.
I am familiar with AA's procedures. I studied and used them from about 1961. One of the reasons I ran so many curves is that I was interested in the so called compensating development, such as water bath, special formulas etc. I ran the curves on Plus-X, Tri-X, Tri-X professional, Panatomic-X, and other emulsions whose names I have forgotten. What I found out is that Plus-X didn't respond to compensating development at all. I could lay the reference curve over the DUT and they would match exactly. Quite a shock. I remember a film rated at ASA 250 that responded admirably, but way too grainy, even in 4x5.
I used two methods. One was to contact print a step tablet, the other was to shoot the tablet using an old diffusion head as a light source. I could tell how much support in the shadows I was getting from flare that way. Oh, and the one way that always worked was pre-exposure, sometimes post exposure. I could lift the toe nicely that way.
Plus-X had the straightest middle section of all. Ruler straight. Tri-X had a significantly different toe than Tri-X Professional.
Every meter measures luminance and can allow you to measure the scene dynamic range. A one percent spotmeter becomes an averaging meter for extreme telephotos, just as there is no such thing as a panoramic camera with a fixed lens. It's just cropping for the panorama, and whether a handheld meter is averaging or spot depends on the relative focal length of the taking lens.
The idea that a hand held averaging meter cannot give you the dynamic range of a scene is nonsense. Have you ever read "The Negative", first edition of AA? He explains how to use a meter to obtain dynamic range, if you cannot do that, you cannot even begin to use the zone system. He even described using a tube set into the meter element to do a rudimentary spot meter. I had several Weston Masters which had this homemade accessory. it was pretty neat, but boy, did it rob you of sensitivity!
Look, a metering system is simply some sort of light sensitive material which provides a change in some electrical parameter for a corresponding change in the light level. On it's own, you would simply see a needle move across the face plate. Putting numbers on the face plate corresponding to some light unit (Lux, Ft. Candles, Candles/ft^2, etc) allows you to quantify the responses. What you ultimately do with these numbers is one of the biggest parts of sensitometry as applied to photography. As you say, that application to digital is different than to film, but only because the demands of the digital medium requires it. I could just as easily build an exposure system for film based specifically on highlight placement. Film chose a different route, and, so far as I can tell, the optimum route. If digital and film had developed concurrently, perhaps we would reconcile the two systems so as to avoid the condition we find ourselves, at least those of us raised on film. The new guys, well, they will probably chortle over the Dodge/Burn application. They will have no appreciation for negatives. It took a while in the darkroom with the counterintuitive nature of dodge/burn when I started up.
I am enjoying this exchange, Jeff. It clears the air, and reminds me that in order to most easily grasp the digital concepts, I am better off with my engineering hat than the photographer's hat. I'm in my late 60's and it's too easy to slip into old patterns. Changing hats works well, and I am glad I can do it.
Cheers, and goodnight! (my,oh my! It's 1:17AM here!)
What a detailed and enchanting article, Lawrence. Thanks
I just ran the script, Version Beta 3.4, and it worked on CS2 with no problems. Are you sure that you are running the one for CS2 and not the older one for CS?