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Weekly Chatter:Canon EOS 1Ds file has bright green in shadows
Monday August 2, 2004

Section 1: Canon EOS 1Ds file has bright green in shadows






Digital Capture > Image Processing & Workflow > Canon EOS 1Ds file has bright green in shadows
























AuthorSubject: Canon EOS 1Ds file has bright green in shadows  
Edward McCain
Posted on Thu Jul 29, 2004 8:01 PM

I have been processing some EOS 1Ds RAW files in Adobe Camera Raw (ACR) in Photoshop CS and am having problems with some strong green colors in the shadows of some Saguaro Cacti I was shooting at twilight.

Here is a link to a page with examples of the full image and with a closeup of one of the more problematic (and almost flourescent green) areas:

http://www.mccainphoto.com/Green_Saguaro/

I am starting out with ACR in 16 bit, using either Adobe 1998 or ProPhoto RGB (doesn't seem to affect the colors one way or the other).

I am increasing the exposure by one stop in ACR. I am guessing that this is at least part of the problem. I was shooting at ISO 100 thinking that I would have less noise, but now I am wondering if I should have gone up with the ISO and tried to increase the exposure to get more shadow detail. Would that have improved this situation?

I ended up using the replace color command in Photoshop CS to try to selectively remove the bright color and dull it down. Any other ideas for a fix, if it is not possible to fix in ACR?

Edward McCain
http://www.mccainphoto.com


Edward McCain
Posted on Fri Jul 30, 2004 5:08 PM

Anybody out there???


Bruce Fraser
Posted on Fri Jul 30, 2004 5:44 PM

I suspect this may be a monitor profile issue. I don't see the fluorescent green shadows on the JPEG at the above link�it looks like normal saguaro colors.

(Coincidentally, someone else raised the same problem on the Adobe U-to-U forum, and in their case, it was a bad monitor profile.)

Can you either view the image on another machine, print it, or load something like sRGB as your display profile to see if the problem goes away?


Edward McCain
Posted on Fri Jul 30, 2004 6:05 PM

Bruce,

I am viewing it on a Sony Artisan and on an Apple 23 inch Cinema Display and
see it clearly. It also shows up when I print it on my Epson 7600 using the
Atkinson profile. In fact, I really noticed it when I was printing a guide
print to go with the files to the designer.

I shoot a lot of saguaro cactus photos for Arizona Highways and Sunset
magazine and I have never seen one with the color of green that is showing
up on the left-hand side of the shadows of the cactus at left. Did you click
on the thumbnail and view the larger version of the file?

Edward

On 7/30/04 3:44 PM, "Imaging Revue" <forums@imagingrevue.com> wrote:

> Bruce Fraser writes:
> ----
> I suspect this may be a monitor profile issue. I don't see the fluorescent
> green shadows on the JPEG at the above link�it looks like normal saguaro
> colors.
>
> (Coincidentally, someone else raised the same problem on the Adobe U-to-U
> forum, and in their case, it was a bad monitor profile.)
>
> Can you either view the image on another machine, print it, or load something
> like sRGB as your display profile to see if the problem goes away?
>
>
> ----
> Imaging Revue
> http://www.imagingrevue.com/
>
>

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Gervaise Davis
Posted on Fri Jul 30, 2004 7:35 PM

Edward, the green shadows and in fact overall green show up on my Samsung 213T LCD pretty badly. The whole image looks fuzzy, green and off color. I have never seen this with my 1Ds images UNLESS the file was corrupted, which happened once on a CF card.
If your camera is not generally doing this with images, I would suspect it is just a corrupted CF card and images. If it is happening otherwise, then something else is surely wrong with the camera.

Gerry


Bruce Fraser
Posted on Fri Jul 30, 2004 8:01 PM

I see the fuzziness but not the bright green, which is probably not surprising considering I'm looking at a JPEG in a web browser, but obviously if it's printing, it's in the file.

Increasing the exposure by 1 stop in ACR is a great deal less desirable than shooting 1 stop hotter in the first place, and that may indeed be some of the problem. Digital isn't film, and underexposure is never a good idea with digital. Linear gamma means that half the captured data is in the brightest f-stop, half the remainder is in the next-brightest, and so on. That doesn't leave many bits for the shadows, and it may be that the fairly extreme exposure compensation is taking something that was very dark green and turning it fluorescent simply by making it much brighter.

With most of the Canon cameras, ACR can reliably recover at least half a stop of blown highlight, so I'd recommend staying at 100 ISO and making longer exposures or opening up the lens. I don't advocate deliberate overexposure, but it's almost invariably better to be 1/4 to 1/3 stop overexposed than to be 1 stop under.

It could also be a card corruption issue, though my experience has been that when that happens, the image generally looks a good deal worse than this one.

What happens if you back off on the Exposure slider and use Brightness to brighten the midtones instead?


Gervaise Davis
Posted on Fri Jul 30, 2004 11:51 PM

Bruce, your new book on RAW is so, so great on the explanation of linear versus non-linear. Thanks so much for writing it and the materials in it. Even after five years of playing with digital and PS, I learned more in three hours of reading your new book than the previous five years !!
I still don't understand the code in the chapter on XMP, but I will get there.

Gerry


Allen Pacheco
Posted on Sat Jul 31, 2004 7:14 AM

The Shadow Tint adjustment in the Calibrate section of Camera Raw may have some impact on eliminating the greenish cast in the shadows. Maybe just a little positive adjustment once the proper white balance is set. It also might help to increase the Shadows value a bit as well to drag those tones even lower.

Camera Raw is a great application and very versatile. But this talk of linear data is going to do more to confuse than not. Camera Raw doesn't let you get at the linear data. It doesn't display it nor does it allow you to obtain a linear conversion as an output. Camera Raw is all about delivering an output into one of four color spaces and that's one of its strong suits. When manipulating the various controls you see the results on the processed data, not the linear data. So why even think in those terms? And you will always have more bits to work with than needed. Even in the darkest shadows. This expose-to-the-right talk is popping up everywhere and 99% of the time blown highlights, NEVER to be recovered, are the result. The ability to "rescue" an overexposed shot should never be allowed to evolve into standard procedure.


Bruce Fraser
Posted on Sat Jul 31, 2004 1:23 PM

-->When manipulating the various controls you see the results on the processed data, not the linear data. So why even think in those terms?

To understand what's going on?

By the time you get to the processing stage, the toothpaste is already out of the tube, but if you don't understand how to expose for linear capture as opposed to film, you WILL get noisy shadows and midtones.

-->you will always have more bits to work with than needed

is just flat-out wrong, and I have plenty of shots to prove it. If you get blown unrecoverable highlights, you are obviously exposing too far to the right. Some camera models have a great deal more highlight headroom than others�Canons typically have about 0.5-1 stop, Nikons typically have much less.

My advice to Edward was specific to the 1Ds, but I am not advocating overexposure�I'm advocating correct exposure. If you have to crank up the Exposure control by 1 stop, you don't have a correct exposure. By the same token, if you have unrecoverable blown highlights, you don't have a correct exposure.

It's important to determine the real ISO sensitivity of the camera. Nominal 100 ISO may be ISO 75 or ISO 150, but the on-camera metering assumes it's ISO 100, so you need to know the real sensitivity of the camera before you can trust what the meter tells you, and compensate accordingly (this is true even if you use a handheld meter).

Once you've done that, it's also a good idea to find out how much headroom your camera has with ACR�it can be anything from 0 to 1 stop. Even if you have 1 stop headroom, I don't advocate using it, but if there's a safety net there you may as well know about it, and if there isn't, you need to know that too.

But the bottom line is that digital reacts very differently, and much less well, to underexposure than does film.


Edward McCain
Posted on Sat Jul 31, 2004 1:38 PM

On 7/31/04 5:14 AM, "Imaging Revue" <forums@imagingrevue.com> wrote:

> Allen Pacheco writes:
> ----
> The Shadow Tint adjustment in the Calibrate section of Camera Raw may have
> some impact on eliminating the greenish cast in the shadows.

I probably should have mentioned that I already enlisted some of the
Calibrate tools as follows:
Shadow Tint -3
Green Saturation -31 (yes -31)
Blue Hue -3
Blue Saturation -3

> Maybe just a
> little positive adjustment once the proper white balance is set.

Not sure what adjustment you mean to adjust here.


> It also
> might help to increase the Shadows value a bit as well to drag those tones
> even lower.

I'm a bit leery of setting the Shadows up too high, as I like to keep as
much shadow info as I can (since I'm bumping the exposure already - and from
my guide prints for CMYK, the shadow areas are really looking murky already.
I'm not a expert at CMYK conversions, so maybe I'm way off on my treatment
here.

>
> Camera Raw is a great application and very versatile. But this talk of linear
> data is going to do more to confuse than not. Camera Raw doesn't let you get
> at the linear data. It doesn't display it nor does it allow you to obtain a
> linear conversion as an output. Camera Raw is all about delivering an output
> into one of four color spaces and that's one of its strong suits. When
> manipulating the various controls you see the results on the processed data,
> not the linear data. So why even think in those terms? And you will always
> have more bits to work with than needed. Even in the darkest shadows. This
> expose-to-the-right talk is popping up everywhere and 99% of the time blown
> highlights, NEVER to be recovered, are the result. The ability to "rescue" an
> overexposed shot should never be allowed to evolve into standard procedure.

It seems that I'm hearing just the opposite from Jeff Schewe (who is getting
it from Thomas Knoll) and Bruce. Those are pretty knowledgeable sources in
my book.

>
>
>
> ----
> Imaging Revue
> http://www.imagingrevue.com/




Edward McCain
Posted on Sat Jul 31, 2004 1:45 PM

On 7/30/04 6:01 PM, "Imaging Revue" <forums@imagingrevue.com> wrote:

> Bruce Fraser writes:
> ----
>
> It could also be a card corruption issue, though my experience has been that
> when that happens, the image generally looks a good deal worse than this one.

I have plenty of other exposures from the same card at the same shoot that
are fine. I was even bracketing, but still don't seem to have the shadow
detail. I plan to start using a standard 2/3 stop overexposure when metering
from the Canon.

>
> What happens if you back off on the Exposure slider and use Brightness to
> brighten the midtones instead?

If I back off on the Exposure and use Brightness, it doesn't seem to affect
the shadows as much as the mid-tones. I seem to have better luck pushing the
Exposure and then using Curves to selectively open up the shadows. Both
techniques show the bright green, but I prefer using my own curve to using
Brightness. Isn't Brightness just a simple curve anyway? Wouldn't it be
better to do it after conversion - or is ACR able to "grab" more data before
the conversion so there would be less data loss in a situation like this?

Edward McCain


Edward McCain
Posted on Sat Jul 31, 2004 1:55 PM

On 7/30/04 5:35 PM, "Imaging Revue" <forums@imagingrevue.com> wrote:

> Gervaise Davis writes:
> ----
> Edward, the green shadows and in fact overall green show up on my Samsung 213T
> LCD pretty badly. The whole image looks fuzzy, green and off color. I have
> never seen this with my 1Ds images UNLESS the file was corrupted, which
> happened once on a CF card.
> If your camera is not generally doing this with images, I would suspect it is
> just a corrupted CF card and images. If it is happening otherwise, then
> something else is surely wrong with the camera.
>
> Gerry

This is a (deliberately) out-of-focus area of the image, so that may account
for the fuzziness you mention. I also have plenty of good images from the
same card at the same time, so I don't think it was the card.


Lonna Tucker
Posted on Sat Jul 31, 2004 3:39 PM

Edward,

I suggest downloading the 30 day trial of Capture One (Pro) and see if you have the same results. LT


Edward McCain
Posted on Sat Jul 31, 2004 4:30 PM

On 7/31/04 1:39 PM, "Imaging Revue" <forums@imagingrevue.com> wrote:

> Lonna Tucker writes:
> ----
> Edward,
>
> I suggest downloading the 30 day trial of Capture One (Pro) and see if you
> have the same results. LT

Hi Lonna,

I've tried Capture One about a year ago and didn't think it was worth the
price compared to ACR, but I'll take another look at this particular problem
and see what happens. Thanks for the suggestion.

Edward





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