Photo by: Bill Bertram
Many photographers choose a DSLR for its superior image quality. However, strange it may seem, many DSLRs straight out of the box are not set to generate the highest quality images they are capable of! This is because of the default parameters (also called settings) are set that way by the manufacturers.  But what is meant by quality of an image first of all? As you would expect there are many factors that characterize high quality images. Two of them are capture of maximum detail and recording of the widest possible dynamic range. (Dynamic range is the range of brightness from the darkest shadows to the brightest highlights that your camera can record). In this article we will confine ourselves to parameters in your DSLR that affect these two factors.

Quality of the images is controlled on your camera by a group of parameters that are called “Image Quality” settings. These govern the following –

  1. File format
  2. Size of the image
  3. Compression factor of the image (valid for JPEG formats only)

Let us look at these in more detail.

File format:  Every digital camera must convert the image captured by its sensor into a digital file; in fact this is the fundamental characteristic of a digital camera! A file is a string of ones and zeros and is written in a particular sequence, called “file format” that is understood by other devices like computers to display the image. The most commonly used (in fact you can call it universal) format is the JPEG. The camera takes the data from the sensor, processes this data based on your input parameters (like white balance, saturation, sharpness, etc.) you have set and generates a JPEG file. Since a JPEG file is fully processed, with all the parameters baked in, it is difficult to change them later in post-processing. However, a JPEG file is ready to be used without any post-processing, by every compatible device, including smart phones.

A JPEG format is a lossy compressed format. That is, when a JPEG format is written, the image data is “squeezed” to reduce the file size. This results in loss of image quality but you get a file of reduced size which is easy to handle. Another disadvantage with JPEG format is that it is capable of recording only 16 Million different colors.  Hence, it is prone to “banding” when you change saturation or contrast drastically in post-processing. (Banding is the appearance of color strips or bands in an image without smooth transition between them).  Also, the dynamic range is lower in JPEG images. This results in blocked out shadows or blown highlights in a high contrast image.

Another format that was once popular is TIFF. TIFF format is uncompressed and hence there is no loss of quality. However, TIFF files are huge in size. Very few use TIFF these days and many cameras do not even support TIFF.

The other file format which is widely used, especially by advanced photographers is the Raw format. Raw format is unprocessed and is also proprietary. That is, there is no universal definition of a Raw format. Thus, reading a Raw format and then displaying the image needs to have specialized software which is known as a Raw converter. The camera manufacturer provides this but many third party software packages are also available.  Raw format’s main advantage is that the input parameters you have set are not processed (or baked) into the file but are kept separately. However, these are used by the Raw converter just to display the image. Since Raw file is unprocessed it is easy change the parameters (like white balance, saturation, sharpness, etc.) in post-processing. Only when you write a file in another format (like JPEG) from the Raw file will these parameters get baked in. Compared to JPEG which has 16 million colors, a Raw image can have 68 billion colors (or even more) and hence can withstand heavy amount of editing without banding. This is also why Raw format is preferred by those who want to create monochrome images. Also, a Raw file can record a larger dynamic range compared to a JPEG file and hence can handle high contrast scenes much better.

The main disadvantage of a Raw file is that it is proprietary to a manufacturer. Worse it changes almost with every camera model (even from the same manufacturer). Hence, you need to keep upgrading the Raw converter whenever you change the camera. They are also very large in size, several times larger than JPEG files thus needing larger storage space. Interestingly, neither the Web nor printers accept Raw files. So, you must use a Raw converter to change the format (to TIFF or to JPEG, mostly the latter) for these applications. For this and other reasons, post-processing is a must for Raw files.

One question you may have is that, why start with Raw and finally land up with a JPEG? Is it not easier to straight away generate an in-camera JPEG? That is a good question!  It is better to start with a  Raw file as you have much greater leeway in editing and better control over various parameters as just explained. Thus, you will get a superior quality JPEG file through Raw conversion than an in-camera generated JPEG.

Size of the image:  One of the most widely used and talked about specification in a digital camera is the pixel count. This tells you how many pixels the image captured by a particular camera will have. The pixel count is measured in mega pixels or MP. This number is erroneously referred to as “resolution” by many but that is incorrect! Pixel count is one specification that almost every photographer looks at when buying a camera but it is not as important as it is made out to be, as you will see. It has a very strong bearing on the size of the print you want make. Printing is generally done at a resolution of 300DPI (dots per inch) or 9000 dots or pixels per square inch.  So, if you want to print an image at a size of 10” X 12” (that is 120 square inches) you will need a pixel count of 120 X 9000 pixels or around 11MP. If you crop an image then you will need an even higher number of pixels to be recorded by your camera since you will be discarding pixels while cropping. Thus, the pixel count has a significant bearing on the size of the prints you want to make.

On the other hand, computer monitors and HD TVs have a pixel count of only 2MP! This comes as a shock to many, since even if you start with a 24MP camera you will end up only using 2 MP if you display an image on the Web or a HD TV!

The image size parameter in your camera allows you to record images with less pixel count than the maximum specified. For example, if you have a DSLR with 24MP, there will be a provision to capture images with lesser pixel counts, say 12MP and 6MP. These are generally called “Medium” and “Small” sizes and the full pixel count image is called “Large” size.

This option is provided to create smaller sized images for less demanding applications like Web display or for display on HDTVs. Smaller images are also easy to handle, need less storage space and are easy to send by electronic mail. Despite these advantages, I recommend that you always photograph in Large size unless there is a very strong reason. This is because, you can create a Small or Medium (down scaled image) image from a larger image but the reverse is not possible without loss of quality. Also, you paid for the full pixel count and you might as well use it! If you have chosen Medium or Small size for whatever reason, make sure that you go back to Large size since if you forget, you will have a problem as just explained.

The image size setting is applicable in most cameras only for JEPG files but some cameras allow you to generate a smaller sized Raw file too.

Image compression: This is sometimes confusingly called the “Quality” setting though in the strict sense it is only one of the factors affecting the overall quality of the image. This setting is applicable only to JPEG images. As you have just read, when a JPEG file is created, data is compressed to make the image file size smaller. Note that it is the image file size (in Mega Bytes) that gets smaller but not the image size in mega pixels! Unfortunately, when this done, there is some loss in quality of the image. The quality, as you would expect suffers more when the compression factor increases. Usually cameras have three compression factors of 4, 8 and 16 and are referred to as Fine, Normal and Basic respectively.  A compression factor of 4 (Fine compression) means that if the original file had 24MP and is 48 Mega Bytes in size, then the compressed file will also have 24MP but will only be 12 Mega Bytes. This smaller file size comes only at the expense of quality as already explained. Once again I must state that if you start with a file with Fine compression you can always get a Normal or Basic compressed file out of it but the other way is not possible without loss of image quality. Also, if you are post-processing a JPEG image, then it must be captured with least compression (Fine) always!

Conclusion: It must be obvious to you by now that the larger the file size, greater will be the quality. Since cost of memory (either cards used in camera or disk space on a computer) is constantly coming down, it is best to use the image settings that give you the highest quality, since as already explained, you can get a lower quality image from a higher quality image while the reverse is not possible. Hence, if you want to cover all risks the best choice is to choose a full pixel count (Large) Raw along with a Large JPEG with least compression (Fine). If you find that the size of the files thus generated (a 24MP camera will generate close to 40 Mega Bytes per each image) is too large, you can go for a Large Raw plus JPEG of Small size and high (Basic) compression. These JPEG files may be OK for the Web application but will be too small for printing. They will be useful for sorting out the images as you can browse through smaller files faster. They are also good for emailing. In case you want a high quality JPEG file (Large with Fine compression) you can always generate it from the Raw file through post-processing or even in-camera.  If you do not want to process Raw images at all, then you must choose a Large JPEG with Fine compression.  Follow these tips and you will get your money’s worth from the large investment you made on your DSLR!

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All text © Ashok Kandimalla

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