Coming Into Proper View
Deciding which camera resolution to use has long been an involved process, and has only been made more demanding with the advent of megapixel and HD technology. Here’s a clear-cut account of the necessary topics to heed in order to successfully meet customer expectations.
HD images are created by megapixel sensors, but conform to a standard that specifies a 16:9 aspect ratio, color fidelity (reproduction) and real-time frame rates. These standards include either a 720p (1,280 X 720) or 1,080p (1,920 X 1,080) resolution. Depending on the application, HD can offer some advantages over megapixel, as shown in the two images atop page 94 comparing a 1.3-megapixel image to a 720p HD image with similar fields of view.
The scene captured in the images is being displayed on each monitor with the same level of detail. Note the difference in the HD image; the top and bottom of the image is cropped. In this application, that is fine because the organization does not need to see or record the ceiling. The advantage with HD is that similar resolution is provided to look at key areas but overall storage and bandwidth is almost 30-percent less. HD resolution can also be ideal for applications such as parking lots or warehouses, but not for long hallways, for example, where people walking away from the camera eventually appear only in the top field of view. Note that some megapixel cameras may have cropping features as well to provide the same end result.
What’s Behind Picture Quality
It’s important to note that resolution may not be the same as someone’s perception of picture quality. Whether it’s an analog or digital image, based on the previous discussion, one would expect that a 540 TVL image from an analog camera would look be
tter than a 470 TVL image, and that a 540 TVL image from an analog camera would look better than a 470 TVL image, and that a D1 IP camera would provide a better picture than a 2CIF camera, right? If all things were equal, the answer would be yes; however, sometimes this is not the case and, as we know, customers are quick to point out the difference.
Picture quality is often thought of as resolution, but resolution is just one of the camera features that affect picture quality. Custom settings that can adjust camera sharpness, contrast and compression may improve one part of the image but affect something else. Trial-and-error testing works best for difficult scenes. If an image gets worse, go back to default settings. Beyond the camera itself, other aspects of the system affect resolution and picture quality. The ones we will discuss, specifically lenses and lighting, are fundamental and often overlooked.
The Lens — Different camera lenses affect resolution and picture quality. Lenses themselves have resolution ratings, which are based on a lens’ optical design as well as the quality of the glass used. If you are using a high resolution camera, make sure you select a lens with an equally high resolution rating.
Besides a lens’ resolution, other features should be considered. A true day/night camera with a moving infrared (IR) cut filter and an IR corrected lens is required to offset the change in focal point when the camera focuses on IR vs. visible light. An aspherical lens is designed to capture more light and reduce optical aberrations compared to standard lenses.
Lighting — Lighting is a major factor in the resulting picture quality, and can be broken into three applications:
Indoor lighting in most cases is the easiest to work with, but can offer unique challenges. A camera looking at a glass jewelry case with spotlights, for example, may produce significant glare. In a casino, the camera may be directed at a well lit gaming table, but the surrounding area might be in shadow. A stylish retail clothing store might combine spot and subdued lighting to create a certain atmosphere.
In each of these scenarios a wide dynamic range (WDR) camera should be considered along with an auto or manual iris, depending on the application. A WDR camera will be able to see both light and dark images simultaneously. An auto iris lens will change the amount of light the camera sees, while a manual iris lens will keep light constant.
Indoor/outdoor applications include scenes that combine both natural and artificial lighting, such as a front lobby, a bank of cash registers running alongside large storefront windows, or a drive-thru window. Again, a WDR-based camera should be used to properly handle that mixture of lighting.
The main challenge with outdoor environments is picking a camera solution that provides good images during daylight hours as well as in the evenings when artificial lighting is in play. Even with the best artificial light, a true day/night camera with an IR corrected lens is recommended. Still, some outdoor applications offer some unique challenges. On bright sunny days cameras are subject to glare. At night, lighting may be too low even with the best artificial illumination, resulting in excessive image ‘noise.’
Too often, lighting is an afterthought in the security system design process. It is important to ask about the amount and type of lighting planned or in existence prior to finalizing camera selection.
Answers to Resolution Questions
So what is the right camera resolution for your application? In cases where video analytics, such as license plate or facial recognition are in use, the minimum resolution required is specified according to manufacturers’ recommendations. In some vertical markets, like gaming, minimum camera and recording regulations are clear. However, in cases where a customer simply wants a good system to watch a parking lot or store counter, cover an entrance, or see down a hallway, the answer is more complex.
Helping your customers make the best decision for their application will require a discussion of the various points above, all of which will affect the overall system performance, design and cost. It’s important to understand whether your customer’s expectation is to see a person in a parking lot or to identify the type of currency exchanging hands at a check-out.
When it comes to picture resolution, manufacturers’ data sheet specifications are a useful guide, but are not a substitute for trialing a camera at a customer’s site or even performing camera comparisons. Comparisons are a great way to test one product against another, assuming all other parts of the test are equal.
In today’s market, resolution is rapidly becoming a key consideration as customers demand even better images and technology advancements are finally delivering effective solutions. Informed customers make better decisions, so it’s worth taking the time to explain the various factors and options that affect resolution to your customers.
Dan Cremins is a product marketing manager at March Networks, focused on the company’s line of HD IP cameras and encoders. He can be contacted at [email protected].
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