Part 8 - Digital File Formats and File Sizes

The photographic topics discussed to this point are deeply rooted in traditional film-based photography and are directly applicable to your DSLR. If this blog were truly a primer on traditional photography, this particular post would cover the topics of film types, ASA/ISO settings, film grain, and the differences between negative and positive films. However, since we are focused on digital photography, we are at the point where traditional and digital photography technologies separate.

It’s an understatement to say that photography is filled with variables. Every step of the process, from the initial capture of the image to the production of a final print, contains a minefield of variables that are often counterintuitive and each seemingly awaiting the opportunity to wreak havoc on your photographic project. Compounding the problems imposed by the technical variables is the jargon that has been 100+ years in development. Getting started in photography encompasses the learning of a new language.

The good news is that although digital photography has brought new tools and jargon to the craft, the basic issues remain unchanged.

Image File Formats

When you initially unpack your digital camera and go through the set up procedure, one of the steps is to select a file format to be used when storing the image on the camera's data card. Depending on the camera these selections are usually JPEG, TIFF and RAW. If this is your first experience with image formats, making a specific choice might not seem all that important. However, it is.

For the purposes of this post and to remain consistent with a practical approach for the uninitiated, these are the differences to be aware of:

• Both JPEG and TIFF formats are fully processed digital images generated by your camera, and stored on the memory card when the picture is taken. These images have had corrections and modifications in sharpness, tone, density and color applied.
• JPEG files are digital images, but the file itself has been sent through a data compression program. This means when the file is created, varying amounts of image data have been compressed to reduce the image file size depending on the degree of compression you specified when setting up your camera (low, medium or high). The good news is that you can store more images on your memory device, but in the process some potentially important image data may have been sacrificed – not so good. Generally speaking, any time compression is applied to an image file, something is lost and image quality suffers. The resulting image is never quite as complete as the original uncompressed version. The JPEG format is an image quality versus file size trade-off you must consider.
• RAW is the most recent of the file formats. In this format, an actual image is not generated when the picture is taken. Instead, the image data that the camera “saw” when the exposure was made is sent to a digital file. This file is then made up of all the raw data necessary to make an image. The image itself is not created until you open the file in a RAW image processor. Some digital cameras provide multiple options for the RAW file that attaches a JPEG file (of various quality levels) for use as a preview or sharing image.
• TIFF and RAW files are considerably larger than JPEG files. Makes sense, more data larger files.

If you are itching for more technical clarification on these file formats, start with your camera manual, and then look through some of the reference material available on technical web forums. (dpreview.com is an excellent forum for this advanced level of detail.)

For the purposes of this primer and based on my shooting and digital darkroom experience, I strongly suggest the following:

• If your image editing software, like Adobe’s Photoshop, supports RAW format, use it!
• If you have no way of importing and working with a RAW camera file then first choose TIFF and lastly JPEG.
• On most cameras you are afforded the option of shooting in RAW mode plus a JPEG file with it. If for some reason you need JPEG files, I recommend this option.
  

Fortunately the more popular imaging programs as well as the software provided with the camera by many manufacturers afford you the ability to convert or directly import RAW files.

By selecting RAW as the file format, you have automatically given each of your images a second opportunity at life. The first time was in your camera when you determined the exposure, and now you can make final adjustments to every tonal and quality component of your image as it is imported into your image editing program by the RAW image converter.

If you have saved your image in RAW format, you will also benefit a second time as you become more proficient with image editing software. You will always be able to reopen your original RAW file (containing all the original image information) and apply your new skills. As RAW image converters continue to improve, you will be able to take advantages of these advancements with your older RAW files.


Shown above is the "Image Quality" menu on a Nikon D200. All modern DSLRs will have a similar menu option to establish the file format for storing your images. The yellow highlighted selection is my normal file format choice. I capture a RAW image file PLUS a small JPEG file to use as a quick reference image. Now I have the best of all worlds. A RAW file that takes advantage of my camera's full resolution capability and captures all the critical image information (unmodified), as well as an accompanying JPEG file for previewing and sharing over the Internet, email, etc. The downside is by electing to save two files for every image, I am using more data card storage space per picture. Read on.

Image File Sizes

Any file format you select requires sufficient memory space to store the image before being transferred to your computer. Obviously, the larger the file the larger the memory device required. It’s likely that you are using a digital camera capable of producing images of 6 to 12 megabytes in size. This is the first indication of the memory required to store each image. The Nikon D200 is a 10 megapixel camera and will be used here to demonstrate the storage requirements. The actual size of each RAW image captured by the D200 is nearly 16 megabytes in size. Doing the math, a standard 1 megabyte compact flash card is capable of storing approximately 60 RAW image files. This is a serious consideration when you’re about to embark on a photographic expedition. Take plenty of data cards.

As a result, estimating the number of images that will be taken during a photo session based on the file format selection determines the number of memory cards needed. Professionals estimate their shooting needs, but they also make a habit of carrying a laptop computer on long assignments as insurance. In this way, images stored on memory cards can be downloaded to the computer at the end of each day. The memory cards can then be cleared to be used repeatedly throughout the event.

The silver lining is the declining price and the ever increasing storage capacity of these memory devices. With the ability to reuse memory cards to store thousands of pictures, the cost of a digital film frame is far less than traditional film. Another reason for taking more than one shot of each picture. Digital film is cheap.

I hope this post provides you a starting point as you determine the best file format(s) for your shooting needs. If you have questions or comments, you know where to find me.

Part 7 - DSLR Shooting Modes

Shooting modes were briefly discussed in Exposure posts. It's time to provide some more detailed information.

Virtually every DSLR on the market allows you to specify a shooting mode. Some of the terminology is slightly different between manufacturers, but the verbage is similar enough to apply the shooting modes on a typical Nikon DSLR to other brands.

There is one mode I would like you to forget -- AUTOMATIC sometimes called PROGRAM mode. Your decision to be serious about the craft of photography is reason enough for me to ask you to STOP using automatic mode on your camera. The previous posts covering "Exposure Is Everything" should have shown that using automatic mode is seldom a guarantee that the image will be exposed correctly.

So, I'm skipping automatic mode. Use auto mode for quickie family snapshots.

The three most important shooting modes in context of creative DSLR photography are: Shutter Priority, Aperture Priority and Manual Mode.

Shutter Priority Mode (circled here in red) as displayed on a Nikon D200

Choosing Shutter Priority mode on your camera "locks" the shutter speed to the speed you manually select. With the shutter speed locked in place (shown here as 1/100th of a second), the camera's metering system changes ONLY the f/stop (shown here as F/6.3) to provide the correct exposure.

When would you use Shutter Priority Mode?

Any time you are in a fast-shooting situation (like a sporting event), or when you want to intentionally blur action, having a preset shutter speed is critical to the final effect. These are times when being able to lock a specific shutter speed into the camera is important to your photography.

Although this setting solves one problem, there is STILL a risk associated with using Shutter Priority. If you are shooting multiple images of a subject that moves from location to location within a scene, you run a risk that the f/stop selected by the camera's metering system will be incorrect (similar to the problem with the automatic mode). More on this risk under Manual Mode below.

Aperture Priority Mode setting on a Nikon D200

In this example, this camera is set to Aperture Priority Mode. Now the photographer selects and "locks" in a specific f/stop (in this case F/8) and allows the camera's meter ONLY to adjust exposure (light striking the image sensor) by varying the Shutter Speed (shown at 1/60th of a second above).

When is Aperture Priority Mode appropriate?

As discussed in previous posts on Exposure, the camera's f/stop ultimately determines the amount of the image (from front to back) that will be in focus when the picture is taken. For example, the flower picture below required a very specific amount of depth of field. Enough depth of field was needed to ensure that the front flower was sharp and yet "shallow" enough to ensure that the background was out of focus.

If the actual depth of field (area in focus) was calculated for this picture,
it would be measured in inches and contain only the foreground flower.

As with Shutter Priority Mode, there is an exposure risk involved with Aperture Priority Mode. Because the shutter is allowed to change according to the camera's meter reading, there is the possibility that the shutter speed selected will not provide the best exposure. More about this risk in Manual Mode below.

Manual shooting mode

In Manual Shooting Mode, you control both the shutter speed (shown here as 1/100th of a second) and the f/stop (shown here as F/8) used to take the picture. This is a very good thing.

In Manual Mode there is no doubt that, regardless of the situation in front of the lens, the shutter speed and f/stop you selected will be used.

So, about those risks with Shutter Priority and Aperture Priority. These exposure risks are eliminated when you set and lock both the speed and aperture manually. The fact is that a typical outdoor scene usually changes very little with minor location changes.

In practice, if you took the time to calculate the "perfect" exposure as discussed in earlier posts, this f/stop and shutter speed combination will be good for multiple shots in the same location. However, using Aperture and Shutter priority modes leaves the door open to exposures being automatically changed. This can't happen with Manual mode.


Here's an example of a situation where one f/stop and shutter speed setting was used for an entire shooting session. The day was sunny and the softball game lasted from 10 a.m. to noon. During this time, there was very little change in the light striking the softball field. Before the game began, I took test shots to determine the proper shutter speed (it needed to be fast to stop the action) and f/stop. These settings were entered in Manual Mode and never changed during the course of the game. Knowing the images would be properly exposed, I was free to concentrate on the action of the game.

So, using Aperture and Shutter Priority modes as they were designed to be used is infinitely better than using purely automatic mode. However, at the end of the day, the only way of guaranteeing that the exposure you invested time in calculating will be the one applied is by using Manual Mode.

Given the limitations of Auto, Shutter and Aperture, it's no wonder that photographic instructors would prefer DSLR cameras with no automated metering features in their Photography 101 classes.

Let me know if you have any questions or comments. You know where to find me.