I think you are correct here. However, some of the command line switches have changed recently between the version I was previously using (v 8.05) and the most recent one (v 8.18, May 18, 2006). This led to some confusion on my part.

In the previous version, -m -n -3 caused the file to be converted as raw without white balance and it was not necessary to use the -r 1 1 1 1. In fact, the -r switch previously set the red multiplier only.

In the current version, it is necessary to use the -r 1 1 1 1 switch for raw output without white balance, and -m is no longer sufficient by itself. As you have pointed out, the -n switch is overridden, and I don't see why you previously disagreed with its use in this situation; it is simply ignored. I have compiled the previous version as DCRaw.exe and the current as DCRawb.exe. Here are the verbose reports with the same switches and the same file being processed. As you can see, the results are quite different. At least, the old version showed the multipliers as 16 (for 16 bit output) and not 1 (for 12 bit). A bit confusing. I have not yet figured out a way to get 12 bit output with the -3 switch. Setting the -b to 0.0625 does not work, and one must divide the 15+1 Photoshop values by 8 to obtain the raw data number.

Click to view attachment

If you look at the valid switches as shown by typing DCRaw without a filename, the -m and -n switches are no longer shown as valid, but they are still processed. At least their meaning has not changed, in contrast to the -r switch.

Click to view attachment



I inadvertently uploaded the wrong screen capture, but the same image was indeed processed with the shown results. My post has been edited to show the corrected screen capture. I agree the -w and -H are meaningless with the -r switch.

<edit> Post deleted by author.

Cool, I envision a new pic mode "ER" placed on the Command Dial between Sports and Landscape modes of the EOS 30D MK II. It will be buried in the menus for Rebel and 1-series bodies.

Agreed, unless one happens to have an extremely neutral patch of gray in the image. It's unlikely the centre of the sun is going to be anything less than white, yellow or red, as in the following image of a setting sun which doesn't appear to be clipped.

Click to view attachment

Having experimented with a few conversions using BB's linear mode, I can see no advantage whatsoever in linear conversion. ACR and RSP seem to do at least an equal job of retaining highlight detail, if not slightly better, and without the hassle of devising and applying an appropriate tone curve.

Consider the following shot of a crocodile's response to a tasty pork chop. Detail at the back of the crocodile's mouth is moderately blown. With a straight conversion, the effect is as though the croc has swallowed a dozen light bulbs that are still working.

Using ACR and dual conversion (one at -4 EC) I think I've managed to tame the glow.

Click to view attachment

However, I was curious as to how ACR, RSP and BB's linear mode would handle these partially blown highlights. RSP actually seems to produce the most pleasing result. ACR seems to produce patches of almost neutral grey, perhaps due to greater contrast. BB's linear conversion seems to recover less highlight detail in general. (A word of warning: those of a nervous disposition should not click on 'enlarge').

Click to view attachment

Dave Coffin, the author of DCraw, seems to think that ACR attempts to reconstruct lost highlight detail. That's the impression I also get if I assume that BB's linear conversion mode is providing the true picture.

I'd be interested to learn from those who are using DCraw if they think it can provide greater recovery of highlight detail than commonly used converters like ACR or RSP.

A footnote: I neglected to turn off RSP's 'detail extractor', which is part of the reason the RSP conversion looks better.

All D60 images, BTW.

Linear mapping of the tone values will not improve highlight detail, but will merely remap the lower tone values. Here are some Imitest produced characteristic curves for the Nikon D200 in linear space converted with DCRaw and in gamma 2.2 with Nikon Capture and Adobe Camera Raw (both with default normal tone curves). Also shown is literal encoding for gamma 2.2 and 1.8.

The highlight values are similar, but the three quarter tones in the gamma 2.2 spaces are considerably brighter, as expected. In the quarter tones both ACR and NC roll off the shadow response.

Click to view attachment

With the D200 and Adobe Camera Raw, when the highlights are set just below 255 in ACR, the raw data number is about 3550 in my tests, not 4095 as one might expect. This is consistent with what John Sheehy has also posted. Since the highlights are placed at 3550 in the raw file, there is some headroom.

As for highlight recovery, I am posting some observations for comment. Here are Stouffer stepwedge exposures in 0.33 EV increments. The linear raw conversion without white balance (DCRaw) is on the left and the ACR conversion with default settings is on the right. Stof 03 Step 1 gives an ACR reading of 251 and Stof 05 and Stof 06 (with +EV 0.66 and +EV 1 exposure) are blown in ACR with a normal exposure setting. In the DCRaw conversion, Stof 06 is beginning to blow in the green channel, as indicated by the color shift toward white.

Click to view attachment

With Stof 05, highlight recovery in ACR is possible with a -0.66 EV correction as shown in this screen capture (posted as a GIF to show good text; please ignore the posterization):

Click to view attachment

With Sfof 06, it is not possible to set the highlights to less than 255 even with -4 EV correction and shadow tones are lost:

Click to view attachment

Because of the headroom in the raw file, highlight recovery is straight forward with slight "overexposure", since the raw channels are not blown. However, when the green channel starts to blow, highlight recovery is less successful. If one had used a magenta filter to balance the channels, I am not sure that highlight recovery would work very well.

I see something different. RSP is rendering the clipped colors to grey. ACR is trying to keep a color and tints some areas in a fleshy pink tone, which are neutral in the RSP picture. Then there's a sudden jump to neutral grey patches in some small spots, where apparently the clipping reached a level, which didn't allow ACR to reconstruct any color. This is a known behavior of ACR. But AFAIK it does a better job in reconstructing highlights than any other raw converter.

And this is obviously the case. I just tested out the limits of my Minolta A2 und compared ACR and dcraw's highlight recovery abilities extensivly. My target was the white wall of a house, lit by cloudy sky. I bracketed in 1/3 f stops from +1.7 EV up to +4.0 EV. First, I zoomed to the wall to get an white only frame for using dcraw's capability of analysing a picture and setting the right multipliers (option -a). Using these multipliers, I converted the bracketed shots. The last one with good highlight detail was the +2.7 EV exposure. The next exposure (+3.0 EV) suffered completely blown sections of the white wall. A linear conversion (-r 1 1 1 1 -m) showed the problem: While the red and blue channel contained good details, the green channel was completely blown. I was not able to produce any acceptable conversion - even not using the -H [2..9] option, which is supposed to reconstruct the highlights. All it did, was to introduce a massive pink cast. Looking at the channels, it turned out, that the green channel was simply filled with a way too dark shade of grey (R had an average of 168, B of 117 and G was filled with plain 109). So, what should be white wall with fine detail (rough plaster) got a dirty pink wall with greenish shadows.

ACR does a way, way better job recovering highlights: The channels of the same +3.0 EV overexposed shot were evenly filled with equal shades of grey, containing all detail. Since we know from the above linear conversion, that the green channel is absolutely blown, ACR reconstructs the green channel with detail from the two others, and balances the result that way, that i's a neutral grey. This way, ACR is able to reconstruct even the highlight's in a +3.3 EV overexposed shot. Even the +3.7 EV exposure is ACR able to handle pretty well, not blowing out all the white wall, but leaving some detail. Only the +4.0 EV image is as bad, as the +3.0 EV was with dcraw.

So, recovering highlights, ACR wins hands down. It is possible, to get all information out of the Raw file with dcraw using a linear conversion, but the image has a strong color cast then, and I wasn't able to balance the colors.

In terms of resolving of fine detail, dcraw wins by a small margin. If you have some very very fine detail in the picture, as you find it with fabrics, dcraw has an edge, a small one.

Here I add a sample:
The first row shows the image converted linear with dcraw, the second row converted with highlight recovery of dcraw and the third row the conversion done with ACR. This is a crop of the white wall, exposed at +3.0 EV. One clearly can see, that the green channel is completely blown, and how dcraw and ACR do different things to reconstruct the highlights.

Thanks, bjanes and Dennis for your response. I tend to agree with Dennis that ACR is (some how) able to extract or reconstruct more color detail in blown highlights. I'm not sure if Capture One is able to better these results, but ACR's reconstruction is mostly credible, although the cyan shift in a blown blue sky could be better. (Or maybe not. What do I know!)

I was recently looking at some rain forest shots with sunlight streaming through. This is a very high DR situation. Tree trunks with direct sunlight are likely to be blown, or the shadows are likely to be very noisy, depending on choice of shutter speed.

In terms of detail from the luminous perspective, there's little difference between RSP and ACR. Howver, with a 'daylight' WB, the ACR conversion brings out the green of the moss on the trunk, which I know was there. I've failed to get RSP to produce that credible green.

Sorry, I'm on my 64 system and wouldn't attempt to post images demonstrating this.

Oops! Forgot to address the second part of the quote. How does DCRaw compare with RSP redarding fine detail extraction?

My impression is, that RSP produces more detail than ACR.

When dealing with very high DR situations, one should not overlook the possibility of doing a double conversion, one for highlights and another for shadows, and then blending them digitally. Jeff Schewe describes this process in a white paper on the Adobe web site (he has reportedly submitted an updated version, but it is not yet posted) and Steve Bingham also describes a slightly different method.

http://www.adobe.com/digitalimag/pdfs/highlight_recovery.pdf

http://dustylens.com/luminosity_mask.htm

If the situation is static and several exposures from a tripod mounted camera are possible, then HDR in Photoshop is an even better option.

Bill,
I use this technique quite often but not to recover highlight detail, which one can do with a single conversion and a negative EC, but to reduce noise and improve image quality in the shadows. For example, I'll often blend 2 conversions, one of which has a -2EC setting and the other a +2EC. However, the improvements are fairly marginal and this technique is no substitute for 2 separate exposures.

I'd like to find a good algorithm that automatically aligns images which are slightly out of register, which always happens when attempting to blend two handheld shots. I'm surprised that Photoshop's HDR attempt at aligning images is so poor. I can always do a better job manually, although I have some trouble with precise rotation of the top layer.

I would expect that the 1D MK2 with its fast frame rate would be a better tool than the 5D for providing good shots for blending. With the 5D, whatever the exposure, I'm not able to take 2 shots within a shorter period than about 2/3rds of a sec, which is a long time for things to get out of register, whether it's due to movement of the subject or camera shake.

As you've gathered, I don't like carrying a tripod around.

I've always felt that the fact that people need to do this, to get results, is only a reflection on the primitive state of RAW converters or the post-processing software. There is absolutely no reason why a 16-bit TIFF can't carry all the DR of the RAW file. The amount of shadow DR potential in a 16-bit TIFF gamma-adjusted is astronomical, compared to what is in a RAW file, and a linear 16-bit TIFF (a full conversion but without tone re-mapping) is sufficient.

Post-processing could do any kind of s-curve or zone-based contrast boosts/enhancements.

Blending is awkward, and full of artifacts, and really should only be necessary for multiple shutter events. Even with multiple shutter events, the HDR process should be done to the data in a totally linear state. I don't know why PS CS2 doesn't merge the data in a RAW state, at a higher bit depth, and then convert it. That would make so much more sense, as the linear data is mathematically simple. If you shoot a grey step card at 1/100, and then again at the same ISO and aperture at 1/1000, the ratio of the average level of each square, minus the blackpoint for that image, is *EXACTLY* the same ratio between the two images in the RAW data. The only thing that differs, other than the scaling difference between the two images, is the S/N ratio. There are minor exceptions, of course; the Canon 20D, for instance, is not linear at ISO 100 in the top half stop or so of RAW highlights, due to some kind of data manipulation (the opposite of what you'd expect from saturation).

John,
That might be true. There is more than one way to skin a cat. I imagine that anyone more skilled in PS than I am could do an equal or better job with a single conversion into 16 bit tif than I can do with a dual conversion.

I use the layer mask method described in an LL tutorial here . I adjust the levels of the individual layers before flattening and find the whole process very quick and easy. The only problem is a tendency to getting halos if the EC gap is too extreme between the 2 conversions. But this problem can usually be fixed with the gamma slider in levels with one or both of the layers and/or a greater degree of Gausiian blurring of the B&W mask. If not, then the whole process has to be repeated with less extreme differences in EC.

I've always assumed that a +2EC (for example) conversion will provide more bits for the shadows and provide better quantization, which in turn translates to better tonality in the shadows and marginally better S/N.

You're right, but a 16bit TIFF is much bigger than a Raw file. Further, you have already interpolated RGB triples in a TIFF, so the real deal is still the raw format. It's the smallest file, containing the most information.

Yes, if the raw converter is able to produce a good highlight conversion.

I don't see the dual conversion method relating directly to recovering highlights. Recovering highlights is dependent upon the converter, as you mention. ACR and C1 appear to be best in this regard. The problem is, after applying the negative EC to recover highlights (-2 EC or whatever), it's then difficult to recover the vibrancy and general tonality of the lower mid-tones and shadows from the converted TIF, even if it's in 16 bit.

Dual conversion is the best technique I happen to know which can improve the tonality of the darker parts of an image with recovered highlights.

For the dual conversion method, you need one conversion with good highlights, right? See my picture above. With dcraw, there's not much in the highlights worth a dual conversion.

I need one conversion with good highlights, period. If I think the shadows are slightly degraded as a consequence of a negative EC applied to a wide DR subject, I might think it worthwhile to blend the image with a second conversion which brings out the shadows and improves tonality.

Coincidently, I’ve been gone through some respective tests this weekend.

First, a ‘virgin conversion’ was accomplished by setting Brightness & Contrast to zero (curve tab linear). Thus, blocking any tone curve (as far as I can tell). Everything referring to ACR, ProPhoto RGB @ 16 bit. Exposure was set to max possible without clipping textured highlights.

Then in Photoshop, a Curves’ adjust layer (i.e. an all-brightening sigmoidal curve) + Contrast mask were applied.

Now after comparing with diverse techniques which require blending of multi-Raw-conversions (+/- EC), I don’t see a competitive edge with these procedures.

So it seems that all ‘bit information’ silently lies in said ‘virgin conversion’, which can look quite dark at first. Things just have to be pulled-out, while preventing any damage ofthe highlights.

Peter

--

Peter,
I think you are probably right. As I wrote before, there's more than one way to skin a cat. Photoshop is a complex program and one can achieve a similar end result through different processes.

Whenever I sit down at my computer to process some images, I have a choice of spending the time learning about Photoshop, or processing my images. I have that choice because I'm an amateur, but I generally prefer to spend the time processing my images with the few trusted techniques I'm familiar with.

I see dual conversion as one such technique of achieving a particular, desired end result. The technique seems to be beneficial with some images, but not with others, and it may well not have any advantage at all for someone more aware of the processing options Photoshop has to offer.

Geez! Posting on this site is certainly an exercise in humility .

That's, what I am saying. The quality of the highlights depends on the raw conversion software, period.

Of course, that's true. There's is no loss in tonalities converting a 12 bit raw into a linear 16 bit .psd file, especially, if you do not convert the gamut. If this is the goal, dcraw is your tool.

OK.

Cheers! Peter

--

Just FYI, Lightroom appears to do a much better job at this than the default ACR interface.

I've played a bit around with it to extract shadow details and pull down highlights from a family shoot last weekend, and it seems to be working very well.

I only wish that the 20D's metering system wouldn't overexpose so often (maybe I need to get the meter cleaned up ...).

Well, I can't let this be. I've been under the delusion all this time that doing a +EC conversion will provide more bits to describe whatever data is in the RAW image and consequently provide better tonality in the shadows.

I've just spent some time revisiting some conversions I did a while ago using the dual conversion method, which I thought was serving some useful purpose.

I now find that it was serving no purpose whatsoever. What's really surprising is that a -4EC conversion into 16 bit tif and ProPhoto RGB still seems to retain the full tonality of the RAW image. This leaves me a bit dumbfounded because the implication is, one could convert all images with a -4EC just to make sure one had retained all available highlight detail. There's no disadvantage except the additional time taken making curves adjustments.

The following images have had no sharpness, contrast or saturation adjustments outside of a simple RGB curves' adjustment or blending procedure. They are not finished, processed images. I'm just looking for any qualities that the blended image might have that can't be easily duplicated with curves applied to the very dark -4EC conversion. I can't find any. The slightly greater contrast noticeable in the small crop of the 'curves' adjusted' image can be changed either way. I just think the images are close enough to demonstrate the point and haven't bothered to get them more closely matched.

Click to view attachment Click to view attachment



Click to view attachment Click to view attachment


I don't why the curves preview image looks like that.

My 20D is usually set to +2/3 EC by default. The lowest I generally go is -2/3 for Great Egrets (bright white birds) small in the frame. For ultra-low-contrast scenes, I find that the 20D limit of +2 EC is insufficient. My 20D agrees with my Sekonic L-558 on a white wall.

Seems to be the same with me .


Ray,

IF I may add a proposal … with all humility; being well aware that the following schematic approach can’t be ideal for every scene / image:


/> In ACR, all tonal controls: Exposure, Shadows, Brightness and Contrast are initially set to 0 (- zero -; curve tab linear).

/> Alt/click on the Exposure slider, move it left or right, to find this sweet spot of maximum Exposure which does not produce any relevant additional clipping. I mean, some pixel of the sky seem to be already irrevocably clipped and obviously can’t be recovered. So the task is to find the max Exposure setting which does not *significantly* enlarge these areas.
Admittedly, this step is a little bit a matter of feeling and in general the main ‘rule’ is not to clip any textured highlights. Most typically this ends in a +/- 0.75EC range, but that's of course just a my 'single'-experience.

/> Set the Shadows slider somewhere reasonably towards the commencement of the histogram. Leave Brightness & Contrast at zero. Click OK to process the file from ACR to Photoshop (ProPhoto RGB, 16 bit).

The following three steps can be easily recorded as an Action:
/> Ctrl/click on the RGB composite channel to select everything visible
/> Ctrl + Shift + I to invert the selection
/> Add a Curves’ adjust layer (80% Opacity and Normal blend mode) which then will carry the inverted selection as a layer mask. The curve itself is a quite special one; it is defined by the following 6 anchor points for Input/Output = 31/40, 56/78, 83/124, 114/172, 147/212 and 180/240.

Then, manually operated again:
/> Alt/click on the layer mask
/> Apply an appropriate Theshold to cover & protect only the brightest regions by pure black, while the rest of the mask gets white.
/> Apply a crude Gaussian Blur of some pixel width (maybe 10 or so)
/> Change back to normal view to fine-tune Opacity


Frankly, I’m using this technique since some weeks, it’s simple in essence and I’m surprised how often it works without further effort (referring to respective ‘HDR’ cases which can’t be adequately treated by the ACR global controls only). So at the risk that it doesn’t work here and it’s finally me looking – I’d like to invite you to give it a try.

Peter

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Peter,
Thanks for the advice. I'll give it a try. You are quite right, the brightest part of the sky with the sun trying to burst through the clouds, is totally blown. At a 750th sec at f8 and ISO 100, there was no way I could have reduced exposure significantly without introducing unacceptable (and difficult to remove) noise in the shadows. This is the typical shot where autobracketing would have been useful. It so happened I did have a tripod in the back of the car, but by the time I got it out and set it up and searched for the remote cord, the mist has lifted and the scene was no longer as interesting. Nevertheless, I should have taken a series of handheld autobracketed shots. The bunglings of an amateur I'm afraid.

Well, I followed some of your advice. Couldn't find that special curve with input/output anchor points of 31/40 etc. Where's that hidden ?

The finished image (finished at this stage, anyway) looks like this. This is a screen grab of the 'proof cololors' image in relation to Epson Premium Lustre (paper color on) and K2 inks on the 7600, perceptual rendering intent.

Click to view attachment


On the other hand, a saturation rendering intent might be more appropriate . What do you think?

Click to view attachment

Just to get things into perspective, here's the monitor image with no proof colors, but same adjustments. Satuaration intent seems to be closer to the 'non-proof color' image to my eyes.

Click to view attachment

Ray,

I’m sincerely glad that clipping (due to exposure) does not only happen to me. And in particular I’m glad that my remote proposal obviously did not went so wrong. As a pure amateur, I find that the last rendition communicates the mood of the scene very well. For example, I could imagine that if your family shared this moment, they’ll love it. My eldest daughter would probably suggest to try to crop & isolate the left half (x 0 to 505 or so); but, that’s definitively not the point with an image that was selected and generously offered for HDR test purposes.

Out of interest, at which settings did you finally arrive in ACR and in Photoshop?

IF of interest at your side:
/> I had outlined some thoughts on tonal settings in ACR here. Though I have to admit that I left discussion for some reasons. Anyway, above text could be seen as a supplement, in case that the global tonal controls cannot compensate enough for dyn. range compression (scene to monitor) without causing damage.

/> Referring to this special tone curve (31/40, etc.), in fact it comes from ACR’s presets. It was just extracted to use it Photoshop; it’s an all-brightening slightly S-shaped curve - a very nifty thing (as suggested here) and it has become a key part of my toolbox.

Peter

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Peter,
I can't remember precisely. This is the sort of image which can be reworked many ways, but approximately the ACR settings were, for the latest version above; minus 2EC, zero brightness, shadows and contrast (but maybe contrast was -50) and I might have used an ACR preset linear curve. I then ctrl clicked on the RGB channel, inverted selection and applied an adjustment curve with 80% opacity. The curve would have been similar to the one pictured above. I then selected the lower part of the image, to the base of the tree and including the cows, with the lasso tool and 40 pixel feather. Used levels to brighten the lower part as though it were a separate picture, applied a bit of 'local contrast enhancement' with unsharp mask to the selected part only and bumped up general saturation to +7 with the hue/sat control.

I wouldn't say this is the final image. There's a slight blocking of shadows in the foreground which can be avoided. It's a good image to play around with though. I'm not keen on cropping it but I wish I could soften the abruptness of the blown part of the sky.

The curve you've described with specific anchor points doesn't seem to work for this image.

Ray,

In my eyes that’s an excellent rendition of this image.

And I’m glad that we could approach our views during discussion.

So long! Peter

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Thanks, Peter for sharing some Photoshop techniques. I actually like this photo despite the flaw of a large blown highlight. For me, of course, there's a background experience that I'm aware of, but the viewer is unlikely to be aware of.

The scene is in far North Queensland (Australia), in a World Heritage area, and the mist is rising from the Daintree river, barely visible on the extreme right of the shot. I was driving along an unidentified road going to a mystery destination in what I thought was a national park. I was therefore surprised to come across a couple of grazing cows.

I learned later that the road led to the farm house of a dairy farm that existed before the area had been declared World Heritage.

Interesting discussion all around.

For those using dcraw/ufraw, you might be interested by this webpage I put up a while ago:
Highlight recovery with ufraw

I find that I can recover quite a lot of information from the highlights this way, without getting those weird colour casts that tend to appear usually.

Regards,
Cyril

Old but interesting post. I wonder if the sun in Ray's linear histogram is really not blown in any channel. The histograms look blown to me (see that little peak right in the end of the histogram line), but this does not happens in the end of the histogram as level values seem to have been corrected afterwards by some scaling (probably WB).
This happens sometimes if a RAW developer with less than 1.0 multipliers for the WB is used (like DCRAW for instance).
This is a sample of histogram with green channel clearly blown but using -H 0 (no-clip): WB multipliers in DCRAW {R,G,B}={0.586287, 0.421032, 1.000000}:




Another issue: did you know that scaling from 12-bit RAW to 16-bit in DCRAW uses a slightly greater than 16.0 multiplier?. Maybe this happens only on Canon cameras, but Dave Coffin confirmed this to me as I saw 16-bit histograms with peaks not equally spaced in 16 levels but a bit more (~17 let's say). That means (at least Canon cameras) don't make use of the full 12-bit: 0..4095 range.

If you want a tool to analyse detailed 15-bit histograms find it here:
http://perso.wanadoo.es/gluijk/soft/histo.htm

For practical reasons, most digital cameras do not make use of the full 12 bit (0..4095) range. The pixel of a digital sensor can be likened to a bucket (or well) that collects electrons. When the pixel has collected all the electrons it can hold, this is called full well. The output of a CCD sensor is voltage, which is amplified and presented to the analog to digital converter (ADC). A 12 bit ADC has possible outputs of 0..4095. This output is in units of analog to digital units (ADUs) and this represents the raw pixel value. The amplification is chosen so that at the full well of the sensor, the output of the ADC is at or near its maximum as explained in the reference. In practice, it may be difficult to obtain an exact match, so a little leeway may be allowed and the output of the ADC may not quite 4095. In addition, the sensor response may not be linear near full well, and only the linear portion of the sensor may be mapped to the ADC output.

To test the range of the ADC that is used, one can make a series of exposures until the sensor is saturated and the ADU value no longer increases. DCRaw is often used to examine the contents of the raw file, but I have found that Iris is more convenient, since it has a graphical interface and also has tools to analyze the resulting conversion. To use Iris, one loads the raw file and performs a demosaicing operation, which renders the raw file into an RGB 12 bit form. No white balance is applied, and one can examine the values in the raw channels by placing the cursor over the area of interest. If desired, a white balance can be applied with multipliers. The file can be converted to the Photoshop 15 bit format (0..32,768) by multiplying the channels by 8 or to a conventional 16 bit file by multiplying by 16.

With my Nikon D200 (which uses a CCD), the ADU output at saturation is about 4009, rather than 4095. In the case of Ray's sun disk, the sensor is most likely fully saturated and there is no "underexposure". Canon cameras use CMOS rather than CCD and the pixel outputs a pixel value directly than presenting a voltage to an ADC, but the principle is similar.

Bill