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Kodak ERI technology brings power of RAW format to JPEGs  
Sunday, February 24, 2002 | by
Kodak Professional today has unveiled a technology that aims to combine the workflow ease of JPEGs with the flexibility of the company's DCR (raw) format photos. Called Extended Range Imaging (ERI), the patented technology enables a photographer using one of Kodak's current DCS 7xx or Pro Back models to correct for serious exposure and white balance errors, as well as access the full gamut of colour captured by the camera, even if the original RAW file captured by the camera is gone and only a camera-processed JPEG is staring them in the face. Digital photography has advanced to the point where many current advancements are more incremental than groundbreaking. Kodak's ERI technology definitely falls into the groundbreaking category.

Experienced digital shooters will know that this has hitherto been impossible with JPEGs, since only the RAW file from most any digital camera contains the full range of tone and colour captured by the camera's sensor. As a processed derivative of that RAW data, a JPEG has always been analogous to a finished print, whereas the RAW file is the original negative. Kodak has effectively stood this notion on its head with the development of the ERI-JPEG format, an EXIF 2.1-compliant JPEG that, says Kodak Advanced Development Manager Steve Noble, should be as compatible as any other JPEG coming out of a digital camera today. Tucked into a separate area of an ERI-JPEG file is ERI metadata (additional text or image information separate from the photo itself, but stored within the same file) that enables Kodak software to turn the finished JPEG print back into an unprocessed RAW negative, effectively reversing the processing steps that took place when the JPEG was created.

The key component of this metadata is a difference image. A difference image is a second version of the photo that contains just the tone and colour information captured by the camera but tossed away during in-camera processing out to an sRGB colour space JPEG. Take the difference image, add to it the finished JPEG image, stir in some spicy Kodak image processing and the resulting photo gumbo is a JPEG file that has the colour range and, more importantly, the mistake-correctability of an original RAW file. If this sounds like a Big Deal, that's because it is.

But only if it actually works as described. The good news in that regard is that it does appear to work, and work wonderfully at that. Here's an example of how an ERI-JPEG, processed with Kodak's upcoming ERI-JPEG file format plug-in for Photoshop, can be used to fix a photo that was overexposed by about 2 stops in a DCS 760.


Photo overexposed by about 2 stops,then converted to an ERI-JPEG in a DCS 760 running a beta version of camera firmware. Large portions of the ISO 400 photo are blown out completely, which means recovery of this photo using Photoshop's standard tools is not possible, though it can be improved somewhat

A handful of simple Photoshop adjustments help the photo, but no amount of pixel massaging can make it right. The blown out areas in the sand trap become gray voids of neutral density as the image is darkened

Processing the same ERI-JPEG file through a beta version of Kodak's upcoming ERI file format plug-in for Photoshop rescues the lost detail. The ERI plug-in combines the image information stored in the ERI-JPEG's ERI metadata with the JPEG itself to effectively undo the in-camera processing and return the photo to something resembling its original, raw state. At that point, white balance and exposure errors can be repaired (within the limits of the original CCD data), the output colour space can be changed, with results that closely mimic what would have been achieved if DCS Photo Desk had been used to tweak an original RAW file's processing parameters

Here, the original RAW file was adjusted in DCS Photo Desk to restore the maximum possible detail in the scene, using settings that mirrored those applied to the ERI-JPEG. As you may be able to observe, even in these screen resolution versions of the photo, there are minute colour and tone differences between the RAW and ERI-JPEG versions. This has been true with other scenes as well in my testing; Photoshop's Info palette reveals 2-3 percentage points of difference in both density and colour values at different locations in most images

The key to making this magic happen has been threefold:

  • First, Kodak had to engineer the techniques that would turn the ERI concept into a reality, a process that got underway in 1999, with the bulk of the scientific and computational heavy lifting taking place over the past year.
  • Kodak then modified the camera firmware for the DCS 760, DCS 720X and the DCS Pro Back models to enable the writing of ERI-JPEGs when JPEG processing is switched on in the camera. This has meant adding all sorts of geeky stuff to the JPEG file, including all the same metadata that's found in raw Kodak DCR files to enable their proper processing. Plus the all-important difference image of course.
  • Simultaneously, Kodak developed ERI-JPEG processing software in the form of a Photoshop file format plug-in. The plug-in is invoked when Photoshop detects, for example, that the photo a user has double-clicked on in the Mac Finder or Windows Explorer is an ERI-JPEG. It hands off the ERI-JPEG to the file format plug-in, which then pops up the window shown (below; note that the photo preview is to be enlarged, and the control layout modified, prior to release). The user can opt to open the photo as is, without calling on special ERI-JPEG processing, or enable the ERI capabilities and begin adjusting the processing parameters for the photo. Users of DCS Photo Desk will find the interface to be familiar. Kodak is still evaluating how the plug-in will handle the processing/opening of batches of photos, which is a potential gotcha in the interface of the beta version evaluated here.


ERI-JPEG file format plug-in for Photoshop

With the new firmware loaded, the camera will produce an ERI-JPEG regardless of the resolution or JPEG quality setting selected. The new firmware will not provide an option to create non-ERI JPEGs. The difference image component of the metadata is compressed, and as it represents only the difference between what the CCD captured and what the JPEG hung onto, it's presence in the file doesn't dramatically increase the file size. JPEG file sizes as stored to the card, says Noble, grow only in the range of 10-30%, assuming that the image is close to a proper exposure. As exposure error increases, especially overexposure error, it's clear that an ERI-JPEG can balloon as the difference image itself contains more and more image data captured by the camera that didn't make it into the actual JPEG.

Based on my testing of Kodak's ERI-JPEG technology over the past few days, I'm convinced that it's the real deal. It's not enough for it to just work, though, it also has to fulfill a need. Time will tell if that's the case. But if you've struggled with managing Kodak DCR files in your workflow, because of the need to, for example, convert them to JPEG before generating contact sheets in certain applications, or before handing them off to a client, but you've been loathed to give up the image-fixing prowess of RAW, then ERI-JPEG may be for you. March is the expected release time frame for the ERI-JPEG-enabled firmware, as well as the ERI file format plug-in for Windows 98 SE and later (a Mac version, OS X only, is to come later, perhaps by mid-year). Both will be free downloads from Kodak's web site, and will soon be the firmware that ships in Kodak cameras from the factory as well.

Kodak will be demonstrating the ERI file format plug-in in their booth at the PMA trade show in Orlando, Florida starting today and running through February 27.

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