One of the most basic decisions any digital photographer has to make is the choice of camera settings that govern image file format and the final image file size. Though the camera has a fixed array of pixels on its image sensor it is the camera’s internal software that selects the actual resolution, processes and manages the captured data. By making selections with the camera’s menu system, the photographer can control the actual number of pixels used to capture the image and how much the resulting image file will be compressed for storage.
At first blush it would seem to be a no-brainer; always capture and store images at the very highest quality possible. This isn’t a bad idea at all, but over time many photographers find that they are storing and archiving vast amounts of information and they begin to wonder if they’ve made the right camera settings choices.
Before we dive in I’d like to offer a few thoughts that should be kept in mind.
- First, once an image is captured and the file written, it is what it is. By this I mean that an image captured at a lower file size cannot be acceptably ‘made bigger’.
- Second, not everyone who uses a camera needs huge image files. For example, some cameras are used to take ID pictures which can be made from truly tiny image files.
- Last, we need to think beyond the next three months. As photographers no matter if we use a camera phone or a professional DSLR we are creating a legacy of images. We might only look at them on our computer monitors today, but 50 years from now somebody may need to make a print of the image.
The example camera used in this article is a Canon with 10-megapixel resolution. Not every model or brand offers the same file size and compression options, but this camera is fairly representative of what is available at this time.
Capture Resolution and File Size
The first choice available to the photographer is the size of the captured image file. On our example camera these sizes are called Large, Medium and Small. By selecting the image file size we are instructing the camera on how many of its available pixels to use.
- In Large file size the camera uses all 10 Megapixels
- Select Medium and the camera uses about 5.2 Megapixels
- At Small we are using only 2.5 Megapixels to record our shots.
To put this in perspective we can compare these file sizes to the largest recommended print size that could be made from each. For a high quality print viewed up close (from a few inches to arm’s length away) the Large file can be printed to 8X12 inches, the Medium file to 6X9 inches and the Small file to 4X6 inches.
There are many reasons to select a file size other than full-sized Large but they tend to be purpose driven. Perhaps the images will only be used on the web where a Large sized file would take forever to load. When we shoot an image for our Porter’s website we choose image size Small to capture an image of about the right size for the web. What if you are taking head shots of employees for a company directory publication? In this case the Medium setting would work fine.
If we choose to shoot our cameras in a setting other than Large we are doing so to decrease the amount of handling the files will need in post-capture editing. It is a time saver to shoot our images near the final resolution and size that the purpose requires.
The second choice that photographers have when making file size selections is the amount of compression applied to the image file to make it use less storage space.
File compression is a process that uses special algorithms to compact a file by selectively tossing out redundant information. OK, I agree that this isn’t a very satisfying description of file compression. In classes I tend to use the ‘Origami Example’: Let’s say that our memory card’s capacity is the same as a desk 24” by 36”. Using our 10MP camera:
- Set for uncompressed image files (RAW file format covered soon) we have zero compression to our images and they all measure 8X12”. On our 24X36” desktop we can store 9 images.
- Set to FINE compression (JPEG file format) we have files ¼ the size of the original – now 4X6” – and we can store 36 images on the same 24X36” desktop
- Finally, if we choose STANDARD compression (also a JPEG file format) we now have files 1/16 the size of the original – 2X3″ in size – and we can store 144 files on our 24X36” desktop.
Compression sounds like a nifty way to get more pictures on our memory cards even if we use the full resolution of our cameras. The files simply get “folded” into smaller packets so that they take up less space. And it is a good trick, if only it didn’t ruin our pictures in the process.
Continuing the folded paper example, let’s say that you have taken an 8X12” picture and folded it in half lengthwise and again across its height. This would be the same as the FINE compression setting. Then we fold the picture one more time in each direction and we have the STANDARD compression setting.
Now completely unfold the picture and lay it out flat. You will notice creases all over the image and in many places the creases distort the picture causing a loss of image information. This is similar to what happens when an image file is electronically compressed for storage on a memory card. The greater the file is compressed the greater the loss of information and detail.
As we can see with the above example, even the FINE setting used on a JPEG type file can cause some information loss. So what if we want zero loss of detail or image quality? If this is what we want we select an uncompressed file type from our camera’s menu. On most cameras this will be called a RAW file type and as the name would imply the raw and unprocessed image data is saved directly to the memory card.
RAW Uncompressed Files
RAW files (or NEF in Nikon cameras) are a special file format that can only be opened using the camera manufacturer’s unique file readers. RAW files are usually made up of two parts: the straight image data captured by the camera’s sensor and a smaller ‘side-car’ file that contains all of the camera settings such as white balance and sharpening information. Third party software companies such as Adobe can license the RAW file readers for their own products (Photoshop, Elements etc.) but email readers such as Hotmail or Yahoo won’t be able to open a RAW file.
The RAW file type is a large subject and there is considerable debate about how to effectively use this file type. For example, photographers can’t print or post images directly from RAW. A RAW file must be resaved as another acceptable file type before it can be broadly shared. However there are several advantages to RAW files that make their use attractive:
- As noted, a RAW file is uncompressed and isn’t processed through the camera’s computer where camera settings are applied.
- Because the camera’s sensor can capture a greater range of light than a computer monitor or a photographic print can render, it is possible to alter the image exposure value by up to 1.5 stops over / under the captured exposure. Once processed into a JPEG file type this exposure latitude is lost.
- RAW files will seem to be less sharp than a JPEG captured at the same time of the same subject. This is because the sharpening settings of the camera haven’t been applied. Many photographers find in-camera sharpening to be overdone and artificial looking. A RAW file can be sharpened in post production to fit the photographer’s taste.
- The white balance of a RAW file can be changed in post processing.
- For the technically inclined there are a number of attributes in RAW files that can impact the way they work.
For another discussion on the pros and cons of RAW files please see THIS BLOG ENTRY
As stated in the beginning of this article, our best advice is to shoot in the largest file size with the least compression your camera offers. In fact, some cameras offer the ability to capture and save both a full-sized RAW file and a large lightly compressed JPEG file. If your camera can do this by all means use this feature.
Not every situation requires large file sizes and low image compression. We mentioned ID photos, images exclusively for the web, and even small images for print publication as examples. However a photographer shooting only a dozen or so images for these purposes would be better served leaving their camera at their highest quality settings and downsizing the images in software after the fact.
RAW, uncompressed files offer great latitude in post production editing but these files cannot be easily shared right out of the camera. RAW files must be opened and resaved in a more universal file format such as JPEG or TIFF. RAW files are also the largest in size and will require more storage space for archiving.
No matter the file type and compression selected please remember that the camera will retain these settings until the photographer changes them. Forgetting to reset the camera to full resolution image capture after a day spent shooting low-res EBay images can seriously ruin your day!