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Capturing in RAW vs JPG

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Introduction

This article explores the difference between capturing digital photographs in camera native raw format and JPG format. Digital SLR cameras capture 12-bits of data per pixel. Some of the newer, high-end digital SLR cameras now capture 14-bits of data per pixel. This is a tremendous amount of granularity to capture at each sensor location (pixel) - 4,096 tonal values for 12-bit cameras, and 16,384 tonal values for 14-bit cameras.

The camera has a filter placed in front of the sensor that filters the light at each pixel for either red, green, or blue light. Downstream processing applies further color algorithms so that each pixel location is provided a red, green and blue value. This downstream processing can occur either in-camera or later on the computer, depending on what capture format you choose.

Camera Native Raw Format

The camera native raw file format differs among camera manufacturers. Each manufacturer prefers to define their own proprietary format so that they may store proprietary information inside the raw file. They feel it optimizes the output from their camera when you use their post-processing software. The one exception is Adobe's Digital Negative (DNG) format. This format has been adopted by several camera manufacturers as their camera native raw file format. What is common among all the raw file formats is that they store the raw pixel data that comes straight off the camera's sensor without any in-camera post-processing. The user must perform all of the post-processing on the their computer after-the-fact.

Benefits Of RAW

Because raw files store the sensor data as it comes straight off the sensor, the user is provided with all 12 or 14 bits of data per pixel that the camera can capture. In post-processing, this data is run through computer software that then generates red, green, and blue color values for each pixel and stores it in a 48-bit color depth RGB file format. For 12-bit raw files, these RGB files contain 4096 tonal values per color channel. This means each pixel can represent one of 68,719,476,736 (16.7 billion) colors. For 14-bit raw files, these RGB files contain 16,384 tonal values per color channel. This means each pixel can represent one of 4,398,046,511,104 (4.3 trillion) colors. The net result of this is that a raw file contains more granular tonal information that retains enormous detail in the shadows and highlights, and can represent a very wide range of colors. Another significant benefit of capturing images in raw format is that the post-processing software on the computer allows the user to make adjustments and refinements to each image that optimize it based on the content of the image. This includes setting the white balance, white point, black point, gamma (brightness), contrast, color corrections per color channnel, degree of sharpening, saturation, and the amount of color and luminence noise reduction.

Limitations Of RAW

Raw files retain a significant amount of shadow and highlight detail, and can represent a enormously wide range of color. They also require a sigificant amount of disk space for storage, and a significant amount of time from the photographer to manually perform post-processing. Most post-processing tools let the photographer perform batch processing to save time.

JPEG Format

JPG is short for JPEG, Joint Photographic Experts Group. It is a standard file format for storing graphic images. This file format permits users to compress image data to reduce file size, but it comes at the expense of image quality when the file is viewed later, and tonal and color range. The algorithm used in compressing JPG files is called a "lossy" compression algorithm. As it compresses the image data, it evaluates and throws away data never to be recovered.

Benefits Of JPG

When you capture images in JPG format in the camera, the camera performs all of the post-processing for you. You select parameters on the camera for white balance, sharpening, hue, tone, saturation, color space, etc. The camera applies your settings to the image sensor data and saves the output in a JPG file format. This is a fully-baked image file ready for viewing. No further intervention is reuqired on the part of the photographer.

Limitations Of JPG

The higher degree of compression the photographer chooses, the more information the algorithm will throw away. Every time a JPG file is opened and resaved, the compression effects are cummulative and the image continues to degrade. It may not be noticeable the first or second time a JPG file is saved, depending on the degree of compression chosen, but it will become noticeable at some point in the form of posterization (noise). Capturing in JPG file format eliminates work for the photographer, but it also imposes certain limitations. It permits few, if any, adjustments to be made after-the-fact. Remember that opening and resaving a JPG file degrades it's quality each and every time, and that this degradation is cummulative. Another limitation of the JPG file format is that it only supports 8-bit color depth. That means it can only store 256 tonal values for each of the red, green, and blue color channels, or 16,777,216 (16.7 million) possible RGB colors per pixel. This translates to less tonal granularity than raw files. It compresses the tonal range and color range of the source raw data, forcing dark shadow detail to be pushed to black, bright highlight detail to be pushed to white, and compression in the mid-tones that can be visible in the form of color banding in some images. Color banding is when you see a hard band of color transition from one area of an image to another instead of smooth tonal transitions.

Conclusion

When choosing whether to capture images in JPG or camera native raw format, it is important to understand the benefits and limitations of each format. JPG files require less space and require no post-processing, but also cannot retain the tonal granularity and color depth of the camera native raw file format. A 12-bit raw file can represent 4,096 times more colors and tones than a JPG file. A 14-bit raw file can represent 262,144 times more colors and tones than a JPG file.