Copyright Tim Grey
All rights reserved.
If you’ve been confused by the issue of resolution in digital imaging, you’re not alone. It can be a confusing topic, and it seems that manufacturers and software makers are conspiring to keep you confused
Copyright Tim Grey
All rights reserved.
If you’ve been confused by the issue of resolution in digital imaging, you’re not alone. It can be a confusing topic, and it seems that manufacturers and software makers are conspiring to keep you confused. It all comes down to pixels, the individual points of a particular color that combine to form a complete photographic image. To understand resolution, we need to understand how those pixels are used, and how information about them is presented. So, let’s cut through the hype and confusion and gain a better understanding of resolution.
Count versus Density
One of the immediate sources of confusion related to resolution is that it refers to two different aspects of an image: the number of pixels in the image versus the density of those pixels. While both are related to some degree, there are important differences.
The pixel count tells us how many pixels are in a given digital image file. That count gives us an idea of the potential output size, but it doesn’t give us any information about the quality of the image.
Pixel density, on the other hand, tells us something about the quality of the image. It tells us how closely the dots are all packed together, which is directly related to the amount of detail in the final image. However, density alone doesn’t provide any information about the total output size of the image.
When we combine pixel count with pixel density, we can get a better idea of the overall quality and dimensions of a particular image file. Then we just need to understand how the various descriptions of resolution are used, what they mean to photographers, and how to ensure we are getting the best results from our digital images.
Digital cameras are an example where resolution is provided as a pixel count rather than pixel density. Resolution is described in megapixels, with each equaling one million pixels.
With megapixel resolution, you are being told how many pixels your digital camera can “see”, but you aren’t being told how clear its vision is. You can get an idea of how big a print you can make, but you really can’t make a judgment on image quality based on the camera’s resolution number alone.
Translating the megapixel count into potential print size can be a bit tricky. For many photographers it might make sense to provide, along with the megapixel number, an indication of what the comparable scan resolution would be. I don’t think too many digital photographers realize that a six megapixel digital capture is the equivalent in terms of pixel count to a 35mm slide scanned at about a 2000 dpi film scan. However, this isn’t a fair comparison. Digital images can be interpolated to a much higher degree than film scans, and film scans do lose some quality in the scanning process.
So, trying to use existing benchmarks to determine output size proves to be very challenging. Instead, I find it helpful to use a rule of thumb with each megapixel size available. For example, I consider three megapixel digital SLR cameras capable of output of excellent quality up to about 11”x17”. For the six megapixel cameras you can essentially match the quality of film up to about 16”x24”, with very good prints up to 20”x30” or larger possible.
Of course, we’re talking here about pixel count versus pixel density. Just because you have a three megapixel sensor doesn’t mean you can produce excellent 11”x17” prints. Especially for the “point-and-shoot” digital cameras, there are a variety of factors beyond resolution that affect image quality. Sensor quality, pixel size, lens quality, in-camera processing and other factors have a big influence on final image quality. Remember, the megapixel resolution value tells you about potential output size, not image quality. You’ll need to test that for yourself (or take someone’s word for it) to determine if a particular camera can provide the quality you need.
For photographers who are either still capturing images on film, or who have file drawers full of slides, a film scanner provides a bridge to the digital world. Unfortunately, film scanning offers its own sources of confusion related to resolution. Scanning straddles the fence of pixel count versus pixel density. A scanner operates at a particular pixel density (scan resolution) to produce a file with a particular pixel count (pixel dimensions).
Most of the confusion over film scanning tends to come from the options provided in the scanner software. I generally recommend that all film scans be done at the highest optical resolution supported by the scanner. This provides a simple solution to the confusion over scan resolution, and also ensures that the digital image you perfect can be printed as large as possible later.
To set the scanner