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Ray
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« Reply #160 on: May 15, 2006, 08:00:26 PM »
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As for ETTR, why look for the small white spike in the histogram? --it wouldn't even be visible at a distance. As discussed previously, the histogram may indicate clipping when there is none and using it for exposure may result in underexposure. Why not just meter from a highlight?
[a href=\"index.php?act=findpost&pid=65605\"][{POST_SNAPBACK}][/a]

I've found that Dale Cotton's suggestion for a reasonably accurate ETTR exposure works quite well. You might have come across it in a previous thread. Essentially, use the spot meter on the brightest part of the image, which could be a fluffy white cloud in a landscape, or a white paper napkin on a table indoors. Use a shutter speed 3 stops slower than the spot meter reading. Voila!
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digitaldog
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« Reply #161 on: May 15, 2006, 08:02:22 PM »
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>The Gray Cards within the WhiBal™ system have both *a and *b Lab channel values of less than 1 >at D50 and are spectrally "flat".

According to the spec's for the BabeColor white it's a* and b* are -0.08/-0.04 so if we buy into the spec's, it's a significantly better piece of plastic. The actual spectral plot from 400nm to 715nm are provided (and while it's pretty flat, it's not perfectly flat as you'd expect). So the spec's given seem to be more "real world" and not as ambiguous as the other product. Further it says it's thermally stable and water proof.
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Andrew Rodney
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bjanes
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« Reply #162 on: May 16, 2006, 11:50:36 AM »
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>The Gray Cards within the WhiBal™ system have both *a and *b Lab channel values of less than 1 >at D50 and are spectrally "flat".

According to the spec's for the BabeColor white it's a* and b* are -0.08/-0.04 so if we buy into the spec's, it's a significantly better piece of plastic. The actual spectral plot from 400nm to 715nm are provided (and while it's pretty flat, it's not perfectly flat as you'd expect). So the spec's given seem to be more "real world" and not as ambiguous as the other product. Further it says it's thermally stable and water proof.
[a href=\"index.php?act=findpost&pid=65609\"][{POST_SNAPBACK}][/a]

A possible limitation of the BabeColor for white balance is that it has a reflectivity of 99% and it likely is the object with the highest luminance in the shot, excluding specular highlights. If the color channels are slightly blown in the target, ACR will not permit a white balance to be taken. That is one reason why a light gray target is preferable for white balance.
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« Reply #163 on: May 16, 2006, 12:41:59 PM »
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A possible limitation of the BabeColor for white balance is that it has a reflectivity of 99% and it likely is the object with the highest luminance in the shot, excluding specular highlights. If the color channels are slightly blown in the target, ACR will not permit a white balance to be taken. That is one reason why a light gray target is preferable for white balance.
[a href=\"index.php?act=findpost&pid=65690\"][{POST_SNAPBACK}][/a]

Not sure. Here's the test I just did (it may be valid, may not; I'm grasping at all this too).

Shot a Macbeth Color Checker (24 patch) with the Babelcolor target in full sun (clear blue Santa Fe sky). My Minolta Flash meter set for incident light gave me a perfect F8 @ 250th at ISO 100. I set the Canon Rebel XT to manual and bracketed (F8 normal then F7.3 and F6.1 for over and F9 and F10 for under exposure. This is the smallest manual bracket in F stops the camera allows).

Brought all the RAW files into ACR in film strip mode, turned off all the Auto settings. F8 (the "normal" exposure) does seem to be the best as the White tile reads 250/251/252. Any other bracket either blows it out to 255 or is under exposed with respect to white. This leads me to believe that the ISO of the camera is correct based on using this external meter.

The white isn't white (but it's close). Note that the Macbeth White in the "correct" exposure reads 246/247/248. So it is neutral but not as white as the white Babel target. Using ACRs White Balance eyedropper on the Bable target produces a value of 252/252/252 (the instructions suggest that 253/254/254 is expected but I assume this is "close enough"). For grins I tried to up the exposure to get another value out of this white so I could save all this as a new ACR default. Setting the exposure to 0.1 did this. Color seems to be a bit better with the white balance on this white square. All the gray squares in the Macbeth read neutral within 2 values of all RGB numbers.  

As for other colors, well they might need work (like using the ACR script). The calibrate tab would help with reds and such. But it appears with the Auto settings off, the highlights are pretty darn close to where they need to be just below clipping IF (big if?) we assume that this white tile is where it should be based on the LAB values I got off of it and the 99% reflectance.

Long story short, I don't see that simply using it to white balance is an issue. Whites, blacks and grays are neutral numerically. Did using this as my exposure guide produce optimal EFTR? Can I use this for any other images?
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Andrew Rodney
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bjanes
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« Reply #164 on: May 16, 2006, 03:13:53 PM »
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Not sure. Here's the test I just did (it may be valid, may not; I'm grasping at all this too).

Shot a Macbeth Color Checker (24 patch) with the Babelcolor target in full sun (clear blue Santa Fe sky). My Minolta Flash meter set for incident light gave me a perfect F8 @ 250th at ISO 100. I set the Canon Rebel XT to manual and bracketed (F8 normal then F7.3 and F6.1 for over and F9 and F10 for under exposure. This is the smallest manual bracket in F stops the camera allows).

Brought all the RAW files into ACR in film strip mode, turned off all the Auto settings. F8 (the "normal" exposure) does seem to be the best as the White tile reads 250/251/252. Any other bracket either blows it out to 255 or is under exposed with respect to white. This leads me to believe that the ISO of the camera is correct based on using this external meter.

The white isn't white (but it's close). Note that the Macbeth White in the "correct" exposure reads 246/247/248. So it is neutral but not as white as the white Babel target. Using ACRs White Balance eyedropper on the Bable target produces a value of 252/252/252 (the instructions suggest that 253/254/254 is expected but I assume this is "close enough"). For grins I tried to up the exposure to get another value out of this white so I could save all this as a new ACR default. Setting the exposure to 0.1 did this. Color seems to be a bit better with the white balance on this white square. All the gray squares in the Macbeth read neutral within 2 values of all RGB numbers. 

As for other colors, well they might need work (like using the ACR script). The calibrate tab would help with reds and such. But it appears with the Auto settings off, the highlights are pretty darn close to where they need to be just below clipping IF (big if?) we assume that this white tile is where it should be based on the LAB values I got off of it and the 99% reflectance.

Long story short, I don't see that simply using it to white balance is an issue. Whites, blacks and grays are neutral numerically. Did using this as my exposure guide produce optimal EFTR? Can I use this for any other images?
[a href=\"index.php?act=findpost&pid=65698\"][{POST_SNAPBACK}][/a]

For white balance with the Macbeth CC, Bruce Fraser and others suggest using the second patch in row 4 (OD 0.23, reflectance 59%, pixel value 202 with gamma 2.2). Patch 1 (OD 0.05, reflectance 89%, pixel value 242) also works but I think the rationale of patch 2 is to have better WB in the darker tones in case of non-linearity. The BableColor has 99% reflectance, OD 0.004, and pixel value 244 with gamma 2.2. A bit of overexposure would saturate the color channels and white balance would not be accurate and ACR would not allow it. Why not use a more conservative gray value?

Bruce is your buddy and business partner--why don't you get his input and tell us why he prefers R4C2 in the CC?
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61Dynamic
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« Reply #165 on: May 16, 2006, 04:48:01 PM »
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Brought all the RAW files into ACR in film strip mode, turned off all the Auto settings. F8 (the "normal" exposure) does seem to be the best as the White tile reads 250/251/252. Any other bracket either blows it out to 255 or is under exposed with respect to white. This leads me to believe that the ISO of the camera is correct based on using this external meter.
The numerical value for a properly exposed white item should read between 238 to 242. If you are getting 250, I'd guess off the top of my head you are about a half-stop over.
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Long story short, I don't see that simply using it to white balance is an issue. Whites, blacks and grays are neutral numerically. Did using this as my exposure guide produce optimal EFTR? Can I use this for any other image
Yes, as you mentioned more exposure in this case resulted in clipping you obtained optimal ETTR for your camera and shooting conditions. (I'm assuming EFTR is "expose for the right") And yes, this can be used for any other image you have taken under the same light. If the exposure and light intensity remained the same (as in no fluctuating flash output cloud cover, etc), you can use that one frame to set exposure correction for the others as well.

Some thoughts on the Babel vs Whibal:
If absolute accuracy is needed in controlled situations, then the Babel I'm sure would be worth the extra cost. However, in most situations the WhiBal works jim-dandy and provides very good White-balance results. The bigger problems for most usage in my opinion is making sure you use it right and keep it clean. If you aren't careful, color casted light can reflect off the card and have an adverse effect on the results (sometimes quite severely). This should go without saying, but I've gotten quite a few files from clients where the card results were worthless since they had the thing tilted wrong.

One thing I like about the WhiBal is that it is neutral throughout the plastic which makes it quite durable. If the thing gets dirty or stained I can scrub it clean or even sand it down with fine-grit sand paper to restore it to like-new operating conditions. I didn't see any info on the Babel site indicating a similar feature.
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digitaldog
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« Reply #166 on: May 16, 2006, 05:50:16 PM »
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The numerical value for a properly exposed white item should read between 238 to 242. If you are getting 250, I'd guess off the top of my head you are about a half-stop over.

Why? I thought the idea for EFTR was to get as close to blowing out white as possible without doing so. The L value of the target used is pretty close to L99 (I measured it with my EyeOne). I could see not wanting the Macbeth white to be there and instead around 240 but this white tile is about as white an object I'll ever encounter no?

Quote
Some thoughts on the Babel vs Whibal:
If absolute accuracy is needed in controlled situations, then the Babel I'm sure would be worth the extra cost. However, in most situations the WhiBal works jim-dandy and provides very good White-balance results. The bigger problems for most usage in my opinion is making sure you use it right and keep it clean. If you aren't careful, color casted light can reflect off the card and have an adverse effect on the results (sometimes quite severely). This should go without saying, but I've gotten quite a few files from clients where the card results were worthless since they had the thing tilted wrong.

They do tell you to keep it clean and NOT to scratch it.

So lets forget the white tile as a device to set white balance (although it seems to work fine) and instead use the above logic to say that using my external meter set to ISO 100 to get an exposure does produce a white that's close to ideal. Now the question is, how do (or can I) correlate this to the internal meter? My thought is it's seeing the world as 18% gray. In theory, if I placed a gray card in the same scene and got the same exposure (F8@250th) then my assumption would be the in camera meter is "correct" for EFTR. If it's not, I would need to use some exposure compensation to produce an in camera exposure that syncs up with the Minonlta. Does that sound reasonable?

Again, this is built on the assumption that exposing the white tile based on my Minolta produced the best exposure of the bracket series to be just shy of white clipping. At least using ACR (my preferred converter) with all Auto settings off.
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Andrew Rodney
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« Reply #167 on: May 16, 2006, 07:41:50 PM »
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Why? I thought the idea for EFTR was to get as close to blowing out white as possible without doing so.
Correct, but that doesn't lead to correct exposure, just optimum capture information. Exposure is optimized after the fact in the raw converter.
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The L value of the target used is pretty close to L99 (I measured it with my EyeOne). I could see not wanting the Macbeth white to be there and instead around 240 but this white tile is about as white an object I'll ever encounter no?
Sometimes you may encounter whiter than white such a something with a slightly stronger amount of light shining on it that still needs to maintain some detail.

And that leads to one thing that needs consideration; highlight detail. If 250 were the optimum value for a properly exposed white object then that means you only have 5 values of tonal difference between that white object, something glowing white or a specular highlight for example. That is not much for the eye to discern between. 238-242 is the range for optimum whites while maintaining visible detail in those whites not to mention a natural appearance.
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They do tell you to keep it clean and NOT to scratch it.
Sure, keeping it clean is something to strive for but when out and about things can get dirtied. I bought the 1st generation WhiBal when it first came out and at the time they were advertising its durability in stating that scratches would not effect readings since the plastic is neutral throughout. Based off this information, while not recommended by them I'm sure, the WhiBal can be recovered if the worst was to happen.

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So lets forget the white tile as a device to set white balance (although it seems to work fine) and instead use the above logic to say that using my external meter set to ISO 100 to get an exposure does produce a white that's close to ideal. Now the question is, how do (or can I) correlate this to the internal meter? My thought is it's seeing the world as 18% gray. In theory, if I placed a gray card in the same scene and got the same exposure (F8@250th) then my assumption would be the in camera meter is "correct" for EFTR. If it's not, I would need to use some exposure compensation to produce an in camera exposure that syncs up with the Minonlta. Does that sound reasonable?
The White tile certainly can be used for WB but over time I have discovered the light grey square does provide better results more often. The difference is usually minimal and the times the white does not work properly is typically when there is a channel clipping or it is very close to channel clipping.

As to syncing the camera and meter, correct. This will give you proper exposure, or as proper as possible given the mechanical limitations of the equipment. This will not however set you up for using expose to the right as that involves over exposure. How much over-exposure depends entirely on the scene and what information you want to keep and throw away.
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bjanes
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« Reply #168 on: May 17, 2006, 06:38:48 AM »
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Correct, but that doesn't lead to correct exposure, just optimum capture information. Exposure is optimized after the fact in the raw converter.

This will not however set you up for using expose to the right as that involves over exposure. How much over-exposure depends entirely on the scene and what information you want to keep and throw away.
[{POST_SNAPBACK}][/a]

Dynamic,

I think that you are being a bit dogmatic and overbearing. As you should know, Andrew is an expert in digital imaging and color management and his views should not be dismissed lightly.

You seem to be using the definition of overexposure for negative film. With digital, the situation is somewhat different as summarized by Bruce Fraser in another post on the Adobe Forums involving exposure to the right:

"For the purposes of this discussion, 'overexposure' means blowing highlights you didn't want to blow, and "correct exposure" means holding exactly the highlight detail you wanted to keep. In terms of what the camera meter tells you, that may well translate to systematic overexposure, but that's because the meter isn't well-suited to digital because it's calibrated to 12% reflectance, which is all the way down at the 12% level in a linear capture."

[a href=\"http://www.adobeforums.com/cgi-bin/webx?14@@.3bbb579c/65]http://www.adobeforums.com/cgi-bin/webx?14@@.3bbb579c/65[/url]

One could define proper exposure as that exposure that optimizes capture information. For Ansel Adams and negative film, that involved exposing for the shadows. For digital capture, it involves exposing for the highlights. The nominal meter reading of the overall scene does not define proper expsure.
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Chris_T
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« Reply #169 on: May 17, 2006, 07:29:51 AM »
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I've found that Dale Cotton's suggestion for a reasonably accurate ETTR exposure works quite well. You might have come across it in a previous thread. Essentially, use the spot meter on the brightest part of the image, which could be a fluffy white cloud in a landscape, or a white paper napkin on a table indoors. Use a shutter speed 3 stops slower than the spot meter reading. Voila!
[a href=\"index.php?act=findpost&pid=65608\"][{POST_SNAPBACK}][/a]

As mentioned in a few other threads, this is the same technique used to expose chromes in a film camera to preserve the highlight details. Nothing has changed except for the introduction of a new acronym ETTR.
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digitaldog
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« Reply #170 on: May 17, 2006, 07:40:39 AM »
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Dynamic,

I think that you are being a bit dogmatic and overbearing. As you should know, Andrew is an expert in digital imaging and color management and his views should not be dismissed lightly.

Thanks however, I'm still trying to ensure that all this expose to the right, use the white tile stuff is working and makes scenes to me and others. I'm in the same boat with the rest of you <g>.

If there were a way to photograph an object and objectively evaluate that I was placing the most bits in the last stop (and I'd have to recognize real data from noise), that would be useful.
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Andrew Rodney
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bjanes
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« Reply #171 on: May 17, 2006, 08:51:55 AM »
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As mentioned in a few other threads, this is the same technique used to expose chromes in a film camera to preserve the highlight details. Nothing has changed except for the introduction of a new acronym ETTR.
[a href=\"index.php?act=findpost&pid=65783\"][{POST_SNAPBACK}][/a]

ETTR is similar to the exposure of chromes, but with chromes one exposes so that the tone placement is where it is desired in the final image. In ETTR, the image might be too light without exposure adjustment in the raw converter.
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61Dynamic
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« Reply #172 on: May 17, 2006, 11:31:36 AM »
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Dynamic,

I think that you are being a bit dogmatic and overbearing. As you should know, Andrew is an expert in digital imaging and color management and his views should not be dismissed lightly.

You seem to be using the definition of overexposure for negative film. With digital, the situation is somewhat different as summarized by Bruce Fraser in another post on the Adobe Forums involving exposure to the right:

"For the purposes of this discussion, 'overexposure' means blowing highlights you didn't want to blow, and "correct exposure" means holding exactly the highlight detail you wanted to keep. In terms of what the camera meter tells you, that may well translate to systematic overexposure, but that's because the meter isn't well-suited to digital because it's calibrated to 12% reflectance, which is all the way down at the 12% level in a linear capture."

http://www.adobeforums.com/cgi-bin/webx?14@@.3bbb579c/65

One could define proper exposure as that exposure that optimizes capture information. For Ansel Adams and negative film, that involved exposing for the shadows. For digital capture, it involves exposing for the highlights. The nominal meter reading of the overall scene does not define proper expsure.
[a href=\"index.php?act=findpost&pid=65780\"][{POST_SNAPBACK}][/a]
I'm well aware of who Andrew is. If I'm not mistaken, he was asking a question and I was answering it. On that note, I'm not being dogmatic or overbearing. I'm simply stating what I know to work.

I have nothing to argue with Mr Fraser's quote -he's absolutely correct, as are you in your last paragraph there- but our discussion is not the one he was in. For the purpose of this discussion I am stating that over-exposure is where tones appear too bright, were 18% grey is lighter than 18% grey, were colors appear washed out, etc. Since this discussion has included post processing and not just capture, I'm referring to correct exposure as the final appearance of the image; what you'll take to print.

Just as you stated, "In ETTR, the image might be too light without exposure adjustment in the raw converter." I'm saying the same thing.

Quote
Thanks however, I'm still trying to ensure that all this expose to the right, use the white tile stuff is working and makes scenes to me and others. I'm in the same boat with the rest of you <g>.

If there were a way to photograph an object and objectively evaluate that I was placing the most bits in the last stop (and I'd have to recognize real data from noise), that would be useful.
[a href=\"index.php?act=findpost&pid=65785\"][{POST_SNAPBACK}][/a]
People are a good subject to test ETTR on. Have someone hold the white balance tool and make sure there some items or clothing that are dark toned and that there are some shadowed areas that will still relay some detail. Bracket photograph them and then see what appears the best.

I'm fairly confident that you'll see that a exposure in that test resulting in the whites being 250 the person will appear washed out and when corrected to 240, the person will appear as they should. You should also see a reduction of noise in the darker areas of the ETTR shots and sometimes -depending on the lens, camera resolution, photographic technique, etc- you might see some added sharpness in mid-tones to highlights.
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bjanes
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« Reply #173 on: May 17, 2006, 01:00:53 PM »
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I have nothing to argue with Mr Fraser's quote -he's absolutely correct, as are you in your last paragraph there- but our discussion is not the one he was in. For the purpose of this discussion I am stating that over-exposure is where tones appear too bright, were 18% grey is lighter than 18% grey, were colors appear washed out, etc. Since this discussion has included post processing and not just capture, I'm referring to correct exposure as the final appearance of the image; what you'll take to print.

[a href=\"index.php?act=findpost&pid=65802\"][{POST_SNAPBACK}][/a]

I don't see where you ever defined what you meant by proper exposure, but in Andrew's test he exposed according to the reading of his Minolta meter and brought the images into ACR without any exposure adjustment. Obviously, if you want 18% gray to appear as 18% gray in the print, you will have to adjust the exposure in ACR. However, in the context of ETTR, the image was not overexposed and Mr. Fraser was quoted in the proper context.
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61Dynamic
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« Reply #174 on: May 17, 2006, 01:57:16 PM »
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I don't see where you ever defined what you meant by proper exposure...
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My apologies if there was any confusion as to what I meant by "proper exposure" but now I have defined what I mean so people can understand what I was talking about.

If everyone here wants to define exposure how Fr. Fraser did then I'm down with that (as I said before, it's not wrong). However, if so, then how should setting exposure correction in the raw converter to set the proper luminosity of the final image be defined? How about "output luminosity?"
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bjanes
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« Reply #175 on: May 17, 2006, 02:58:02 PM »
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My apologies if there was any confusion as to what I meant by "proper exposure" but now I have defined what I mean so people can understand what I was talking about.

If everyone here wants to define exposure how Fr. Fraser did then I'm down with that (as I said before, it's not wrong). However, if so, then how should setting exposure correction in the raw converter to set the proper luminosity of the final image be defined? How about "output luminosity?"
[{POST_SNAPBACK}][/a]

Output luminosity is fine with me. IMHO, exposure should be applied to what is done in the camera and is defined in lux seconds and can not be changed after the fact. We can argue what proper exposure is, but Bruce's definition of overexposure makes sense to me.

In terms of translating ISO settings to output luminosity, the ISO saturation standard for digital cameras indicates that an 18% gray card exposed according to the standard should read 18/106 of full scale, or a pixel level of 696 at the output of a 12-bit A-to-D converter, which can represent 4096 levels. Assuming a gamma of 2.2, the pixel value would be 114 with 8 bit output.

[a href=\"http://www.normankoren.com/digital_cameras.html]http://www.normankoren.com/digital_cameras.html[/url]

Julia Borg has a nice table relating reflection values and pixel values for various gammas:

http://www.pochtar.com/gamut_view/gamma.htm

Of course, raw converters apply a tone curve as well as a gamma correction so that the output of ACR would be somewhat different.
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« Reply #176 on: May 17, 2006, 03:38:05 PM »
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A somewhat interesting update. I purchased a version of RAW Developer (Michael mentions it in his recent article "Measuring Megabytes"). I've played with a demo for a few months but decided that today with V1.5 out running native on Intel Mac's, I'd go for it. Nice product. Anyway, what's interesting is that bringing in the "correct" exposure Macbeth with BabelColor tile done yesterday, the default rendering produces nearly identical RGB values for white, gray and black in that RAW converter as ACR with Auto off. Other colors are different (the red is much better in RAW Developer*). I didn't expect the default renderings exposure wise to be so darn similar with different converters but when you think about it, that's what SHOULD be happening.  

RAW Developer R152/G92/B62
ACR R182/G104/B72
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« Reply #177 on: June 01, 2006, 02:45:05 AM »
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Not to get too OT, but since were talking about the WhiBal and the BabelColor, what about the Expodisc gizmo?
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« Reply #178 on: June 01, 2006, 07:44:18 AM »
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Output luminosity is fine with me. IMHO, exposure should be applied to what is done in the camera and is defined in lux seconds and can not be changed after the fact.

This "exposure" you refer to is a very important one to consider.  It is really the one that is the starting point for determining S/N ratios; once you have chosen this "absolute exposure" as I call it, then the choice of ISO is really counter-intuitive, based on popular belief.  The highest gain-based ISO will give the least noise, unless the camera does a really horrible job of high-ISO amplification.  The only issue with going high with the ISO is clipping (again, assuming absolute exposure is fixed).  The choice of ISO with the manual exposure affects the "digitization depth" or the histogram.

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In terms of translating ISO settings to output luminosity, the ISO saturation standard for digital cameras indicates that an 18% gray card exposed according to the standard should read 18/106 of full scale, or a pixel level of 696 at the output of a 12-bit A-to-D converter, which can represent 4096 levels.
[a href=\"index.php?act=findpost&pid=65824\"][{POST_SNAPBACK}][/a]

About 350 is what is used in practice (for green; for red much less).  By the standard you mention, cameras are overstating their ISO by about 2x.
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« Reply #179 on: June 01, 2006, 08:31:49 AM »
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Bruce is your buddy and business partner--why don't you get his input and tell us why he prefers R4C2 in the CC?
[a href=\"index.php?act=findpost&pid=65704\"][{POST_SNAPBACK}][/a]

It's pretty simple really. The reason we white-balance rather than gray-balance is that the midpoint in a gamma 1.0 capture (level 128 in 8-bit terms) is a light gray around Lab L* 76. R2C4 on the Macbeth is a little lighter than this, R3C4 is quite a bit darker, so R2C4 is the closest patch to the midpoint.
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