Parametric Image Editing

Parametric Image Editing (PIE): An introduction

Parametric image editing is a class of non-destructive image editing in which the editing software does not alter original files, but instead records changes to images as sets of instructions or parameters. Software that adjusts images in this way — like Lightroom, Adobe Camera Raw (ACR), Aperture, Bibble, and Capture One — is particularly well suited to the challenges of digital photography, as we’ll see. And because you can save your work as a set of instructions, it’s the adjustment method that best suits a DAM environment.

As we think about how to build a digital image collection, it will be important to get a good understanding of how parametric settings are created, applied and saved. It’s significantly different from the pixel pushing one does in Photoshop, and it offers many clear advantages (and a handful of disadvantages). Once you understand how PIE works, you can realize significant gains in efficiency and security, no matter which parametric image editing software (PIEware) you use. To read more about the development and context of non-destructive image editing, check out this white paper from Adobe.

It starts with the raw ingredients

Before we get too far into parametric image editing, let’s make sure we have a good understanding of what’s unique about raw files, since that’s what really propelled the development of PIEware. Raw files from each camera model are unique. So a NEF or a CR2 that one camera model creates will have a different structure from a NEF or CR2 that a different model creates. Furthermore, proprietary raw files are undocumented, which means that the manufacturer does not disclose the way the data is stacked up in the file.

Because altering an undocumented file format is dangerous, third party applications for adjusting raw images (that is, applications from companies other than the camera manufacturer) generally don’t alter the raw file. In order to make changes to the image, they reinterpret the image, save the user’s changes as rendering instructions, then send the image through a rendering engine that decodes the raw data and makes the user’s changes.

While this inability to adjust raw files was a severe limitation when digital photography was young, it has been turned into an advantage now that computers have gotten more powerful and as the software for reinterpreting raw files has improved. This has led to a world of image editing that is of great benefit to the digital photographer.
Read more about raw files in the format section

Making and saving adjustments

Because you cannot re-mosaic rendered raw files, rendering them is a one-way street. When you are working with PIEware, you are never pushing the original pixels around. Instead, you are creating a set of instructions to tell the software how to adjust the image as it goes through the rendering pipeline. When you save the changes you’ve made, you are never altering the original source image — instead, you are saving a set of instructions. If you are working on a proprietary raw file, those instructions are probably saved in a sidecar file (Figure 1). For DNG or a rendered file, the instructions can be saved back to the file itself.

Figure 1 When you adjust proprietary raw files with PIEware, the instructions are typically saved in a sidecar file that lives in the same folder and has the same rootname as the file.

Rendering engines are unique

Although many PIEware applications have controls that look similar, as seen in Figure 1, programs cannot use the rendering instructions that another program has created. So, the effect that you create with Fill Light in Lightroom is similar to the one that you create with Aperture’s Shadow, but each program’s rendering engine uses different algorithms to make the changes. Even if the syntax of the rendering instructions looks similar, the programs are not doing the calculations in exactly the same way.

In fact, it’s important to understand that any parametric adjustments you make in one program cannot be seen by any other program that does not have access to the same rendering engine (using the DNG format can help you get around this, sort of). It’s like the difference between French and Italian — they are similar, but definitely not interchangeable. At this point, each piece of PIEware speaks its own language, and that’s not likely to change any time soon.
Read more about how DNG makes renderings portable in the Format section

Figure 2 Both Apple's Aperture and Adobe's Lightroom offer similar functionality, control and interface. But the rendering instructions created in one do not translate to the other. The underlying engines are different.

Advantages of parametric image editing

While parametric image editing has been around for a long time, it did not really catch on until the widespread practice of raw file photography. The limitations of raw file adjustment forced users into a parametric editing environment. What started as a limitation has become a great advantage in efficiency, in terms of time, storage space, and creative flexibility.

Non-destructive workflow

Since you cannot alter raw files, PIEware doesn’t even try. With PIEware, all changes you make to images are simply instructions, or parameters, to interpret the source data differently. In order to return to an image in its default state, you simply get rid of the rendering instructions (or tell the software not to pay attention to them, if the software allows that).

Paste settings easily

One of the most common needs in digital image editing is the ability to adjust multiple images in the same way, as shown in Figure 3. Since most raw images can benefit from some level of individual attention, you’ll often want to apply one image’s changes to other images. What can be an onerous chore in Photoshop is a trivial task in PIEware. Simply copy the adjustments from one file to another, and you’re done.

Figure 3 One of the advantages of working parametrically is that you can paste the adjustment instructions from one file to others that need the same treatment.

Save and compare multiple interpretations

When adjusting an image, you might want to try one set of tools and compare the results to what another set provides. Or maybe you want to try out entirely different interpretations of the image — color and grayscale, for instance (see Figure 4). You can accomplish all of this with parametric settings without creating lots of different copies of the image file.

Figure 4 Since each variation produced with PIEware is just a set of instructions, you can experiment with different image interpretations without filling your hard drive with duplicate files. You can save the variations you like as virtual copies and return to them later.

Take advantage of software improvements

In the short life of parametric editing, we’ve seen lots of improvement in the rendering tools. The controls in the first version of Adobe Camera Raw were good, but they pale in comparison to the controls in the most recent version. Because you never change the original file, you can use a new version of the software on an old file, and the results will be the same as if the file had never been touched previously.

And if you keep using the same software package, you’ll generally be able to keep an old adjustment as a starting point, even as new capabilities become available. If the changes you made to your raw files with ACR 4 could benefit by some of the new tools in ACR 5 or Lightroom 3, you can make these changes while either keeping your old work or starting over clean.

Single-image archiving

Because PIEware is getting better at adjusting images, we’re moving closer to a world where you only need to have one copy of each source image, with all versions and variations saved as instruction sets. While we’re not entirely there yet, many photographers now find that the vast majority of their images need only parametric adjustments, so they don’t need to create many derivative files. And if you look at the improvements from ACR 1 through ACR 5 and beyond, it’s hard to see where this trend will end.

Archiving a single source file per image offers some clear advantages. One advantage is that it can cut down the space requirements for your archive. Another is that you can wrangle all your versions inside cataloging PIEware for easier management of the variations. And another is that it can increase the security of the backup, while at the same time reducing backup costs. We’ll look more at that in the next sections.

It’s not just for raw files anymore

The advantages of parametric image editing are not restricted to raw files anymore. The non-destructive workflow that was borne out of a limitation has been extended to rendered files because of the advantages it offers. Now, you can get the same non-destructive goodness with your JPEG and TIFF files that was previously available only for raw files, although not all manufacturers' software does this.

Unpredictability when working with rendered file types

Now that parametric image editing is available for rendered file types like JPEF, TIFF, and PSD, there are some new drawbacks. It’s generally well known that the look of a raw file is dependent on PIEware settings, but most people expect rendered files to look the same from program to program. This expectation can lead to unpredictable rendering of images.

For instance, if you adjust a JPEG file with Lightroom, the image will be displayed inside the Lightroom application with the adjustments applied. If you view this same file with a program that does not understand the rendering instructions, the image will look like it did before the settings were applied, creating confusion, or worse. If you send the image off for expensive reproduction with the assumption that it will show the adjustments, and instead it comes back with the original version showing, someone might suffer a financial loss. If you work with rendered files parametrically, be careful about what images get sent out. Figure 5 shows how this can can work.

Bridge preferences for rendered files

You can instruct Bridge, Photoshop and Adobe Camera Raw how to handle TIFFs and JPEGs that might have rendering instructions included. These settings will control how the program deals with this potentially confusion situation. There are three basic options, as shown in Figure 6.

1. Disable (TIFF or JPEG) Support will ignore any parametric image settings in the file.
2. Automatically open JPEGs with settings that will honor any embedded parametric image settings, and will open these files through Camera Raw whenever you open them into Photoshop. You'll have an opportunity to accept, alter, or delete the settings at that point. (This is our generally recommended setting).
3. Automatically open all supported (JPEG or TIFF) will open all TIFFs or JPEGs through Camera Raw, whether parametric Image edits are present or not.

Figure 6 This image shows the options for handling parametric image edits in rendered files in the Adobe Camera Raw preferences. We suggest this setting for most users for both TIFF and JPEG.

DNG as a parametric image editing solution

Although Adobe has named the format “Digital Negative,” we prefer to think of DNG as a “digital job jacket.” In fact, the DNG format is a wrapper that can contain all kinds of useful information about your image file. Let’s take a look at what can be stored there.

The “negative”

The DNG file can contain all the raw image data (the source image) that the camera puts into its own raw file. This means that you can open a DNG file in ACR and have the full range of adjustment options that you had with the raw file. The source image does not even have to be a raw file. If you adjust a JPEG, TIFF, or PSD file in Lightroom, and then want to bundle up the original image with the adjusted image, you can export as a DNG.

The “paperwork”

Due to the expandable metadata space in a DNG file, you can write all sorts of metadata safely to the file, with virtually no danger of it becoming unreadable or of corrupting the file. The format was designed with the expectation that a user might want to attach lots of information to the file, including classes of metadata that have not yet been invented.

A “pretty good print”

The DNG file can store not only the “negative,” but also a “print.” You can create an embedded preview that reflects all the adjustments you have made. You can correct the color, brightness, and contrast — even crop or apply a curve — and then store the resulting image inside the DNG file. This embedded preview can be of several sizes, including one that is the full dimension of the RAW file.

Private maker notes

If a camera manufacturer comes up with a new way to process a file and wishes to keep the details secret, it can encrypt this information into the DNG file. Thus, DNG files can be universally accessible, while at the same time offering manufacturers protection for their proprietary image-processing algorithms. This will be useful as more manufacturers let users choose DNG as a raw file format to be produced straight out of the camera, or as a processed output from their software.

The original raw files

If you want the advantages of DNG but don't want to throw away your original raw files, you can simply embed them into the DNG file itself. If you embed a raw file in a DNG, you will be able to extract this file at any later date, should you choose to. The inclusion of a data validation hash (discussed below) makes the DNG format arguably the safest place to store your proprietary raw files.

A data validation hash

It's now possible to write a checksum or "hash" into the DNG that can provide rock-solid information about the integrity of the file itself. If you've embedded the source image, there is a hash for this as well.
Read more about DNG validation in the data validation section

dpBestflow® strongly supports the use of DNG as an archive format for parametric image editing.