Why Raw -- Part III

Article and Photography by Ron Bigelow


Raw converter Advantage #7: Sharpening

Sharpening is necessary with digital cameras to offset the small amount of blurring that occurs because of the color filter array. Actually, sharpening doesn't sharpen anything. What it does is increase local contrast (particularly along edges). The human eye interprets that increased contrast as sharpness.

Conventional wisdom holds that sharpening should be one of the last steps performed on an image. This is so because other process steps can decrease the sharpness of the image. If an image is sharpened and then edited, the sharpening may be decreased during the editing. Also, since sharpening adds a certain amount of image degradation, it is not a good idea to sharpen multiple times (there are exceptions to this, but you have to know what you are doing; the exceptions will not be dealt with in this article). This is not a problem for raw. Raw files are not sharpened in the camera. As a result, it is up to the photographer to determine the best point at which to sharpen the file (e.g., in the raw converter or at any point during image editing).

However, this is an issue for JPEG files due to the file compression that occurs in the camera. As covered in Part II of this article, JPEG files are compressed. The compression process creates JPEG squares. The problem is that any sharpening that occurs after compression will sharpen the JPEG squares and make them more visible. Accordingly, JPEG files are sharpened in the camera prior to compression of the file. This avoids the issue of sharpening the JPEG squares. However, this creates two problems. First, image editing of a JPEG file is likely to decrease the sharpness of the image (especially if interpolation is used to increase the size of the file in order to create larger prints). As a result, the JPEG files may need to be resharpened. However, this second sharpening will sharpen the JPEG squares and cause some additional image degradation. This will result in a lowering of image quality. Second, since sharpening is done in camera for JPEG images, the sharpening is burned into the file. Additional sharpening can be applied later, but oversharpening can not be removed. This may limit the editing choices for the image.

Due to the issue of JPEG squares, files produced through the raw process have a sharpening advantage both with respect to image quality and flexibility.

Raw Converter Advantage #8: Color Space Flexibility

There are a number of color spaces available to photographers. The two most common are sRGB and Adobe RGB. Each color space consists of all the colors that space is capable of producing. Some color spaces are broader than others. For instance, Adobe RGB has colors that can not be produced in sRGB. The camera sensor has its own color space. Depending on the camera, this color space may be larger than either Adobe RGB or sRGB. Sooner or later, the native color space of the sensor will have to be converted into one of the more common color spaces.

It is desirable to match the color space of the file as closely to the output device (e.g., the printer or web) as possible. Otherwise, a mismatch between the color spaces will result. This is a significant issue because color space mismatch causes image degradation.

Mismatched color spaces occur when a photographer, or the camera, selects a color space that does not match the output device that will be used. An example would be a camera that assigns an sRGB color space when the images from the camera will be printed on a device that utilizes a larger color space. If the selected color space is too small, there will be colors that the camera was able to produce and that the output device can reproduce but that are lost due to the limited color space selected for the image. These out of gamut colors will either be clipped or altered to fit in the smaller color space (which may cause quantization error). If the color space is too large, the limited number of shades that the file has will be spread out over colors that the output device can not reproduce. Thus, the shades will be spread over a larger range of colors that will increase the distance between the shades and the likelihood of posterization. In short, converting from one color space to another causes image degradation, and the larger the differences between the color spaces, the larger the image degradation. Therefore, it is desirable to select the proper color space and to keep the number of conversions from one color space to another at a minimum.

This is where raw gains another advantage. The raw file has not had a color space assigned to it. Rather, this generally occurs at the time of the conversion. Thus, shooting in raw provides color space flexibility. The photographer can choose the color space that best matches the color space of the device that will be used to present the image. This is especially advantageous when the photograph will be used with more than one output device. In this case, the photographer can perform a separate conversion for each application, individually selecting the color space for each use.

In the case of JPEG, the color space is assigned in the camera and is burned into the file. If it is desired to change the color space at a later time, some image degradation will result. Even if color space changes are made late in the process (any time after raw conversion for a raw file), the raw process still has an advantage. JPEG files will undergo the color space conversion with the eight bits of data that the JPEG files contain (actually, the image editing program may convert the eight bit JPEG file into twelve bits for the color conversion and then back into eight bits; while this may help some, it is still not as good as with raw/TIFF due to quantization issues). TIFF files generated from raw files will undergo the color space conversion with 12 bits of data. This will reduce the amount of image degradation that occurs for the TIFF files.

One final consideration is that additional color spaces could be developed in the future that better suit certain applications. Since raw files do not have a color space assigned, they will be well suited for conversion into these new color spaces.

Cumulative Damage

Each of these issues, by itself, may have a relatively small impact on the quality of an image. That is why it is sometimes difficult to isolate any one of these advantages and demonstrate its impact in a photograph. However, the issue with JPEG images is that they go through a series of actions, each of which induces a small amount of image degradation. This series of image degradations becomes cumulative. This can be seen by studying the workflow of a JPEG file. The JPEG image is converted in the camera using less sophisticated algorithms than third party converters and produces less detail. Next, the image is reduced from 12 to 8 bits, which causes a loss of more information. Subsequently, the image is compressed which throws out more detail and introduces JPEG squares. If the image is, subsequently, edited in an image editing program, the editing will further degrade the JPEG image because it has only 8 bits per color channel (compared to the 12 bits per channel TIFF file that came from a raw process). The JPEG image will now, most likely, require additional sharpening. The sharpening will induce some further image degradation and sharpen the JPEG squares. The JPEG image will have to be saved again. However, each time the image is saved, it gets recompressed. So, additional degradation and JPEG square issues will occur during the process of saving the image.

Conversely, the raw process induces little image degradation. Editing done in an image editing program will induce some degradation, but this will be small due to the 12 bit nature of the TIFF file. Sharpening will also create some degradation. However, overall, TIFF images produced from raw files suffer less image degradation than JPEG files.

Figures 1 and 2 show two images taken from the same file. Both images started as a raw file. Figure 1 followed the standard raw to TIFF workflow. Figure 2 was converted into a JPEG file (using the highest quality JPEG setting) and followed the standard JPEG workflow from that point on. The images were processed to look as similar as possible.

Figure 1: Image from Raw Workflow
Figure 2: Image from JPEG Workflow

At this small size, the two images look similar as far as quality is concerned.

Enlarging the images begins to tell a different story. Figure 3 is a crop (at two times magnification) of a section from Figure 1 (raw workflow). Figure 4 is a crop (also at two times magnification) of a section from Figure 2 (JPEG workflow). Both Figures are of the images before any sharpening.

Figure 3: Unsharpened Image Crop from Raw Workflow
Figure 4: Unsharpened Image Crop from JPEG Workflow
Unsharpened, the raw image does not show much of an advantage over the JPEG image. However, when sharpening is added, the situation changes.

Figure 5 is a crop (two times magnification) of a section from Figure 1 (raw workflow) with sharpening added. Figure 6 is a crop (two times magnification) of a section from Figure 2 (JPEG workflow) with sharpening added.

Figure 5: Sharpened Image Crop from Raw Workflow
Figure 6: Sharpened Image Crop from JPEG Workflow

At these magnifications, both images show some degradation due to the sharpening. However, the JPEG image shows much more degradation. This is particularly an issue when images are going to be enlarged significantly. One of the factors that determines how large an image can be printed is how well it can handle the higher levels of sharpening that is required on large images. Consequently, raw becomes more important as the images get larger.

One thing to keep in mind is that both of these images started life as raw files. The JPEG image was actually converted into JPEG in the raw converter. As a consequence, the JPEG image shown in this section is actually a best case scenario. Had the image been shot as JPEG in the camera, it would have suffered even more image degradation due to the fact that it would have been converted with the camera's converter using less sophisticated algorithms (see Raw Advantage #5 in Part II of this article).

Raw Converter Disadvantages

It is now time to look at the disadvantages of raw.

Raw Converter Disadvantage #1: Processing Time

One of the most common complaints about raw is that it takes more time to process than JPEG. This is one of those statements that is technically true but can be misleading. There are those photographers that spend a significant amount of time fine tuning images during the raw process (usually for fine art or similar purposes). In this case, a lot of time is spent working on the images. However, this is because the photographer has opted to spend the time creating exceptional images, not because of the raw process. For those photographers that just want to quickly process their images, batch processing can be used. The image editing program can be set up with preselected processing parameters (e.g., saturation, contrast, and color space) and the images can be batch processed. This is similar to what the camera does during in camera (e.g., JPEG) processing. While it will take the computer a while to process the images, done intelligently, it should take only a few minutes of the photographer's time. For instance, when I go out on a multi-day shoot, I come back with several gigabytes of images. Once uploaded to the computer, I start the conversion. Then, I unload my gear, take a shower, or eat some dinner. The computer is done converting my images long before I ever get around to reviewing them. This process takes only a few minutes of my personal time, but I now get all of the advantages of using raw. In essence, intelligently planned, the raw process can take very little time.

Raw Converter Disadvantage #2: Complexity

People often fear the raw process because they have heard that it has a complex workflow. In reality, the raw process can range from incredibly simple to incredibly complex -- it all depends on the purposes of the photographer. When it is desired to quickly produce some images for general use (say family vacation shots), a very simple workflow will suffice. For instance, if the raw converter has been properly set up for batch processing, with the correct parameters chosen, images can go directly from raw conversion to the printer with no further manipulation required by the photographer. Even when some image editing is performed, it can often be done fairly quickly. For instance, I have thousands of images on my web site of trails that I have hiked or biked. A large percentage of those images started as raw but required less than sixty seconds worth of manipulation before they were ready to be saved for web use.

Complex raw workflows come into play when photographers want to fine tune the images, often for fine art or similar purposes. In that case, complicated workflows might be used, but it is because the photographer wants to do something special with the image not because it is a raw file.

Raw Converter Disadvantage #3: Storage Space

Raw files will take more space than JPEG. There is no getting around this. However, with disk space being relatively cheap these days, it is not a major issue as far as many photographers are concerned.

Raw Converter Disadvantage #4: Compatibility

Currently, raw files from different manufacturers, and even among some cameras from the same manufacturer, are not compatible with each other. The concern is that, at some time in the future, photographers may find that the new raw converters do not work with the older raw formats. This is a real concern, and each photographer will have to evaluate the risk for himself. Personally, with the huge number of raw files out there, if this did happen, I am sure that someone will develop software to deal with the issue (after all there would be money in it for the software developer).

Do You Need Raw

Not everyone needs raw. Those who do use raw don't necessarily need it all the time. Whether you need raw or not breaks down into four issues: quality, size, flexibility, and complexity.

  1. Quality: As can be seen from these articles, raw has a number of quality advantages over JPEG. Consequently, the higher the quality desired from a final image, the more advantageous the raw format becomes. On the other hand, if maximum quality is not an issue, JPEG may work just fine. Thus, images destined for fine art are best shot in raw. Images of your nephew's birthday party can be shot in JPEG.

  2. Size: The larger the size of the final image, the more desirable it is to shoot in raw. As prints become larger, the quality issues of JPEG become more evident. This is particularly true if a photographer intends to push the size of the print close to the maximum size that the camera can deliver and still hold photo quality. On the other hand, JPEG may be a good choice for smaller prints that do not push the limits of the camera.

  3. Flexibility: Since little has been done to a raw image, other than converting the sensor data to digital format, raw maintains a tremendous amount of flexibility with respect to tonal curves, conversion tools, compression (raw files are not compressed but can be compressed after conversion), color space, white balance, and, sharpening. The more a photographer wants flexibility in the processing of images after capture, the more raw is the logical choice. Photographers that need little flexibility in the processing of images may decide that JPEG is their choice.
  1. Complexity: Complexity is related to the issue of flexibility. Some images are fairly straight forward with no unusual factors that complicate the taking or processing of an image. For instance, an indoor shot of your child, under uniform lighting, would be an example of such an image. Other images can be quite complex with numerous issues. Imagine a shot of the moon descending over a mountain range. Parts of the mountain range are directly illuminated by the first rays of the early morning sunrise. Other parts of the range are still in deep shadow. At the base of the mountains is a white sand dune, also in shadow. Such an image creates numerous challenges. The moon will be many stops brighter than the shadow areas, creating a problem of dynamic range. The sunlit portions of the mountains will be illuminated by the very warm rays (red and yellow light) of the morning sunrise while the shadow portions of the mountains will be receiving very cold light (blue) from the sky overhead. The white sand dunes will be particularly blue due to this light. This will cause issues with color temperature. The flexibility of raw becomes a great advantage with images like this.


I have often heard and read statements such as, "Just get the exposure right in the camera, and you don't need to use raw". Hopefully, you now know better than that and can use your detailed understanding of raw and JPEG to decide which format will work best for your specific needs.


Why Raw -- Part II