The new version is (finally) able to fully harness the wide dynamic range and huge color space of the Foveon X3F output and allow some really compelling photographic results from the sensor.  It is also now capable of directly outputting full-gamut ProPhotoRGB colorspace images in several formats including 16-bit TIFF, which is fantastic if the next step is a ProPhoto native tool like Lightroom or PS CS4+.  Take a look at an example of the kind of conversion control this thing can do, in this case using a very overexposed shot in hazy conditions…

 

Now, obviously this is in the middle of workflow and would have actual editing to do as the next step, but for a "digital developer" app preparing files for Lightroom or Photoshop, this thing has chops.  Definitely enough to make the camera itself a more capable, compelling tool for creative work.  The release of the new SD15 camera is a nice thing, but really the biggest improvements to the platform have been made in the post-process software.  It's enough of an improvement in terms of usable output that it will likely have me revisiting a bunch of my older raw images to make (much!) better gravy out of them.  I'll have to start shooting again in general to make that matter at all (har har) but I foresee having far less frustration with it in future.

Great job, Sigma.  Keep up the good work!

Dear Mr. @@@@,

Thanks for taking the time to speak with me today.  As we discussed, I have made a few small discoveries since our original discussions several months ago, that may shed some light on the red channel overexposure that I have experienced in certain situations using my SD14.  Rather than a capture problem in the camera, I have discovered that the issue may be related to the color-space conversion performed by the Sigma Photo Pro software during X3F import.

I have attached two versions of an image, one that illustrates the color issue that I have experienced in scenes that push the limits of the color space (gamut) used in the current Sigma Photo Pro 2.5 software. The difference between these images is obviously intended to represent a worst case scenario, so please don’t regard the “original” over-saturated image as the work of a talentless hack — it is purely for illustration purposes!

Click to read on –>

1) The “original” image is of a red flower, shot at ISO 50 using the 1.07 firware in my SD14.  This sample image is a direct, zero adjustment 16-bit TIFF export from SPP 2.5, that I have cropped and saved to JPEG (sRGB) using Photoshop with no other adjustments.  Illumination of the original scene was by direct afternoon sunlight, and exposure was spot-metered directly on the brightest surface of the flower petal area. There is no orange whatsoever in the original scene… the flower was purely red.  As you can see, the red channel is completely overexposed across the surface of the petals, and the “orange” areas that appear in the shot seem to be due to green-channel information creeping in through some type of color conversion error.  No combination of adjustments in SPP were able to bring the red channel overexposure into control in a way that was usable as a final image.  The detail is simply “gone”, as you can see:

2) The “new method” image is from the same source file.  Rather than using SPP, I extracted and converted the raw data section of the X3F file to uncorrected 16-bit TIFF using a very clever and useful utility, which was coded for that purpose by an SD14 owner named Pavel Sokolov.  The uncorrected TIFF is very dark, so I brightened it using the Auto Curves function in Photoshop, then made a simple correction to color using the Hue center and Saturation controls, and finally cropped and saved it to JPEG in the sRGB color space.  Using this simple extraction utility, all of the detail in the source file was preserved, and the red-channel oversaturation experienced in Photo Pro was not a factor at all.  The results speak for themselves.  Obviously it’s not a great photo to begin with, but these results are MUCH better than what is possible with SPP given the same source X3F file.

It’s important to note that it is possible to capture this scene without the red overexposure, but in order to do so using the standard “Sigma” software workflow, the overall exposure must be reduced (in-camera) to the point that the blue and green channels are significantly underexposed.  That is not an ideal solution.  Obviously based on these two example images, the camera *is* capable of capturing the visual information, and in fact is doing so very well… it’s just that the range of color that the camera captures seems to be well outside the limits of the Sigma software’s color space conversion capabilities.  The camera works wonderfully, and thanks to Sigma for a fantastic design… but the software could definitely be improved.

Are there plans to update the Sigma Photo Pro software in the near future?  If so, and assuming that limitations in the available output color space options themselves are part of the problem, is it possible for a larger color space (such as the excellent ProPhoto RGB) to be offered as an output option?  That change alone could provide considerable improvements to the results of color conversion at the fully saturated edge of the CIE 1931 chromaticity space.

If such a change (or some other, unrelated improvement) could help to solve the color conversion and accuracy problems that many users have experienced, it could provide both a huge improvement in workflow and in overall image quality for Sigma owners.  Even more, it could result in a potentially huge improvement in the perception of Sigma’s camera products among professional and semi-professional photographers.

I look forward to hearing your thoughts on this, and please let me know if I can provide any additional information or assistance.

Best regards,

Jason Porter
Roanoke, VA

——————–

NOTE TO BLOG VISITORS:  Further discussion of the X3F Extractor Utility is available on the DPReview forums at http://forums.dpreview.com/forums/readflat.asp?forum=1027&thread=28576411

@@@@@,

As we discussed on the phone, I am writing to document my new SD14 camera’s unusual red saturation problem and provide raw X3F samples for your review.

Before I explain, here are the details of my particular unit and configuration:

Sigma SD14
serial no. [redacted]
firmware revision 1.07

Sigma 18-50mm F/2.8 EX Macro
serial no. [redacted]

Using Sigma Photo Pro 2.5 in Windows XP, using a color-corrected display (Spyder2Express calibrated).

The problem:

I have had my SD14 for one week, and like it very much! Unfortunately, I have discovered that it exhibits some unusual behavior when capturing images in bright sunlight. This became most evident when I attempted to capture a close-up shot of a red flowering plant on my front porch. Specifically, the camera seems to hugely over-saturate reds, to the point of total saturation in the red channel at 255 (per the “loupe” feature in Photo Pro 2.5) This behavior is consistent in both Program mode and Manual mode at ISO 100. In order to bring the red saturation down to the point where the red channel ceases to clip at 255, the image must be significantly underexposed in the other channels.

What is particularly disturbing is that I am experiencing significant bloom into the green channel when I capture the same exact image at ISO 50. This occurs in areas of pure red on the subject that (when captured at ISO 100) are totally saturated at 255 red, with zero information in the green channel. When captured at ISO 50 using the same Program mode exposure and metering, the red channel is saturated at 255 and the green channel jumps to around 240 in many areas! This causes the flower to appear bright neon orange with obvious two-tone banding in the image. I can’t imagine that this is normal behavior for capturing an image of a common red flower in direct sunlight, and it was not even a particularly bright day!

I understand that ISO 50 has less “headroom” than the other ISO modes (per the note on the firmware download page), but even when using center metering directly on the brightest part of the flower petals, the saturation problem in the red channel is very much present. Also, this does not explain the green-channel bleed.

The X3F samples:

I have taken a series of raw X3F images of the red flower, for your review. If you have Photo Pro 2.5 on a Windows machine and you can use that to view these, it may be helpful so that we are comparing the same output. These images are all of the same subject in the same ambient light. All images are captured using the Daylight white balance setting on the camera, and using the 18-50mm F2.8 EX lens. I have hosted these files on my own server so that you can access them and download directly at your convenience. These are organized in folders by mode, by ISO, and by exposure.

Direct your browser to: http://jasonporter.us/photography/sigmasd14/

The first files to look at are the P mode ISO 100 and ISO 50 exposures, which are in folders marked “P_ISO100_EvalMeter” and “P_ISO50_EvalMeter”.

The P mode ISO 100 Evaluative Metering exposure (no. 182) exhibits the full red oversaturation I mentioned. The same shot taken in P mode ISO 50 (no. 183) exhibits the green-channel bleed resulting in bright yellow/orange coloration. A revised version of the ISO 50 shot using Spot Metering (no. 187) and metered directly on the red area shows the same behavior, but with slightly lower overall exposure and slightly less green channel bleed.

The rest of the files are captured in M mode to demonstrate the red channel behavior at various apertures and shutter speeds. There are two sequential sets of shots at F/2.8 and F/5.6 apertures, at a series of different shutter speeds, to show both the red channel behavior and the level of general overall green/blue underexposure required to bring the red channel into control. I have also included an F/20 1/15s shot and an F/8 1/250s shot, for reference at smaller apertures… these are both “best case” shots with the red channel just beginning to fully oversaturate.

It should be noted that if the aperture and shutter speed are reduced to keep the red from blowing out completely, the green areas and the background (and the shot in general) are significantly darker than they appeared to the eye. This subject was a balanced mixture of bright red and rich green tones. In fact, the P-mode Evaluative Metering shots that were so horribly overexposed on the red highlights are the closest to being accurate on the green background out of any of the shots, and even so, they are much darker and less saturated on those areas than they should be compared to the actual rich green color of the plant.

Thoughts:

The only clue to the origin of this odd red-channel behavior that I have come across was actually with the help of an open-source Raw converter program called UFRaw. (ufraw.sourceforge.net) It is a simple Raw-converter packge similar to Adobe Camera Raw or Sigma Photo Pro, and it supports the X3F format. Using UFRaw, there is an option available to disable the “Use color matrix” option for the input color gamut (in this case sRGB). Apparently the term “color matrix” is used in that software to refer to the color-space correction factor that is applied when normalizing an sRGB (or other) image source to the workspace. When this box is unchecked in UFRaw, some of the heavy red over-saturation decreases, and quite a bit of detail is restored. Unfortunately, no similar “feature” exists in Photo Pro 2.5. It isn’t perfect, but it is MUCH better than the default “corrected” setting, which is comparable to the look of the image in Sigma Photo Pro.

In any case, it raises the question: Is Photo Pro 2.5 applying an sRGB input gamut correction when it is inappropriate to do so?

I have checked these images on a non-color-corrected display, in order to rule out any potential problem with my calibrated monitor profile. The oversaturation behavior is consistent on all 4 computers that I have checked, including three different Windows XP systems, and an Ubuntu Linux machine using UFRaw.

By the way, I would like to be clear that I’m not naive about digital capture and the necessity of image editing… I have worked with digital workflow for quite a while and I recognize that every shot will require some tweaking to produce a quality, balanced result. With a camera like the SD14 that is designed for creative photography, that is even more true. This saturation problem, however, is not something that I can easily correct in Photoshop, and it’s not something that Sigma Photo Pro 2.5 seems capable of improving. This problem is simply blowing out all of the surface detail in the surface of brightly colored objects, and I don’t think that a 2 or 3 stop (or more) overall underexposure in the camera coupled with manually correcting the levels back up in the green and blue channels in Photoshop is the best way to achieve a professional result. Maybe I’m incorrect on that, but it’s not an approach that I have ever had to take with any other camera.

Thank you very much for your time and consideration, I know this was a long read, and I salute you if you made it through the whole thing. I would greatly appreciate your input and insight on this problem. I look forward to hearing from you.

And again, thanks for making a great product!

Best regards,

Jason Porter
Roanoke, Virginia, USA

P.S. – There is one other issue I’d like to point out, and see if you have experienced it. Some of the Raw X3F files are inexplicably much larger than others. Typical shots at 4.6mp in Raw mode are usually between 9mb and 13mb, but occasionally a file will be almost double in size. Shot number 206 in the F/5.6 set folder is a good example, the file is almost 22 megabytes! Is this a known issue with the 1.07 firmware?