The truth behind the quality of digital photography

The technology of digital photography is advancing rapidly; all commercial brands make efforts to be the first choice among professional photographers looking for the best quality images in the worst light conditions. Each photographer needs are different, but quality is a common factor in all types of photography. This is the reason why it is important to know the characteristics that support it.

The purpose of this article is firstly to determine what is the main factor that contributes to the quality of a digital image and secondly to know in which situations it is important to consider this factor. It should be noted that the information in this article applies to advances in current technology and aimed to still photography (although it may apply for motion picture as well). A few years ago the limiting factors in digital photography were others. The developments of the brands to improve their sensors, and the emergence of new advances in optics, indicate that these are the limiting factors today. This allows to establish as hypothesis: that the quality of the images is directly related to the optics and the ability of the sensor to capture the light.

In order to obtain information that was not affected by the advertising marketing, the data from the camera companies were avoided. Information was collected from different recognized professional photographers and companies in the field of optics and digital sensors.

The number of digital cameras on sale and all the options that exist complicate the decision on how to know which camera will actually give the best results. As a first resource, amateur buyers are usually guided by the amount of megapixels (of the sensor) that the camera offers, this is the feature that is most highlighted in advertising campaigns. The second most popular feature when deciding which camera to buy is the “zoom” range.

Before developing the subject it is important to eliminate these two factors: resolution and zoom are irrelevant and disposable when looking for a camera that offers the best quality. The quality of an image is determined by the ability of the camera to capture the scene with as much information as possible and with the least amount of defects. According to the leading company in quality measurements DxOMark, quality can be measured and scored within four scales:

  1. Depth of color (amount of colors that the sensor can register),
  2. Dynamic range (number of brightness values that the sensor can store),
  3. Noise (sensor errors to determine the information in a pixel).
  4. Perceptual resolution (lens resolution).

As you can see, these factors are divided into two categories, the sensor and the camera optics. Mazzetta, J., Caudle, D., and Wadeneck, B in their article “Digital Camera Imaging Evaluation” agree that quality is mainly determined by the optics and the signal that can be captured by the sensor.

Optical quality

When looking to buy a professional camera, the optics are purchased separately from the camera, so the analysis of the optics and the sensor must be done independently. Speaking of optics, you can differentiate two categories: the lens defects, and the perceptual resolution you can achieve.

Dr. Hubert Nasse in an interview by Granger, M. specifies that the defects of optics are caused by the flashes of light caused by the reflection of a high-intensity light source, such as the sun with the crystals and lens components. To reduce this problem, crystals are used with an anti-reflective coating (a component that significantly increases the price of the lenses that incorporate it). On the other hand, the perceptual resolution is not a defect, it is simply a limitation of the lens. And unlike defects that are only visible at very specific situations, perceptual resolution is a factor that is present in all the photographs. The amount of light rays that the lens can concentrate at one point equates in this resolution. It is important to clarify that previously the resolution of the camera (pixels), was an important specification to consider, but the advances in the technology of the sensors reached and surpassed those of the optics.

The perceptual resolution of the lens is today’s limiting factor of the final resolution of an image, which is why the resolution of the camera (pixels) is currently irrelevant.

Now that the importance of perceptual resolution is clear, it should be noted that even using the same lens, but varying its focal length and diaphragm this perceptual resolution varies considerably. This presents a number of problems, since you can buy a lens with excellent resolution, but if used at its worst focal length or diaphragm range that resolution will decrease.

Kenn Rockwell in his study “Nikon 50mm Lens Comparison” performed a series of tests comparing all the focal and diaphragm ranges of a single lens, his results revealed a very important finding: when looking for the highest perceptual resolution it is more important to know which are the best ranges of a specific lens than to know its overall score, since even the best lens used in an incorrect way will give poor quality results.

Sensor performance

Once the relevance of optics is determined, we must now analyze what happens to this luminous information that is sent to the sensor and processed digitally.

As previously stated in the article, the categorization of the quality of a sensor is: color depth, dynamic range and noise. To analyze the quality of a sensor you must know the work area of ​​the photographer, what kind of photographs will be taken? Each of these three factors may or may not be important depending on the type of photography.

Depth of color

Is a factor that is mainly relevant to portraitists, as subtle changes in skin colors and variations in tone significantly affect these images.

Dynamic range

is a factor that directly affects landscapers, in a landscape there is a great contrast of luminosity between elements so having all the light information stored in the image is very important. (It has to be noted though that outside the realm of still photography, for videographers where raw image formats are limited to the speed of the processing of the camera, then dynamic range is fundamental)

Noise factor

And finally the noise factor is mainly relevant for photographers working in poor light conditions, such as action photographers and reporters, they need a sensor capable of processing images with low noise in low light conditions. It should be noted that color depth and dynamic range are factors that very subtly affect an image and in general terms are not noticeable if the original scene that was photographed is not known. However, noise is a determining factor, an image with lots of noise is even illegible. That is why it is important to focus on how to determine which camera can offer the least possible noise. Noise is a defect that is directly related to the amount of light a pixel receives, if a pixel receives less light than it can interpret noise is created. When the light reaches the sensor the only thing that can affect the amount of light that receives each pixel is its size. The size of each pixel is measured in micrometers. Clark, R. performed a study called “Pixel Size, ISO and Noise in Digital Cameras” in which he compared three cameras with different pixel sizes to determine the importance of this specification, one with pixels of 5.7, another of 4.3 and the last one of 6.5 micrometers. The test results check the ratio of pixel size to the amount of noise generated. The camera with the bigger pixels got better results regarding the noise, because it received more light in each pixel. However, this study also revealed that the difference in quality of these sensors is not visible in good light conditions, only a difference is perceived when ambient light is noticeably bad.

With the information analyzed in this article we can stablish as main determining factors of the quality of a digital photograph: the perceptual resolution of the optics and the noise of the digital sensor.

When to consider them (noise and perceptual resolution)?

We should also understand when is it important to consider these factors in choosing a digital camera. The perceptual resolution is only relevant if the impression or medium where the photograph will be displayed is large enough to notice, otherwise this factor loses importance. Noise is a factor which, as explained above, is only perceptible in poor light conditions. If the photographer has control over the light (for example works inside a photo studio) then the noise will not be a limiting factor because it is directly related to the amount of light that the sensor receives, however in any other situation the noise is an important element to consider.

Choosing a digital camera, like any choice depends a lot on the person who is doing it. Knowing the type of photography you are aiming for is essential in order to select the equipment. It is important to know all the real factors and specifications that affect the quality of an image so that you can compare them with the personal needs of each photographer and define what type of camera to look for and with which lens to equip it with.

I think that the technical aspects are indispensable and must be known in depth. It is very important not to be carried away by the data and information that marketing companies show through consumer advertising and to know how each specification of the camera affects the photographs.

However, a good photograph is more than a good camera or a good lens, it is the creativity, emotion and expression of the photographer.

References

Clark, R. (March 3, 2012). Pixel Size, ISO and Noise in Digital Cameras.

Clarkvision, 2(8). Retrieved March 3, 2015 from http://www.clarkvision.com/articles/pixel.size.and.iso/index.html

 

DXOMark. Measuring sensors using RAW and testing lenses on cameras.

Retrieved March 1, 2015, from http://www.dxomark.com/About/In-depth-

measurements/Measuring-sensors-using-RAW-and-testing-lenses-on-cameras

 

Granger, M. (September 20, 2014).  Interview with a Zeiss Master [Video file].

Retrieved march 1, 2015, from https://www.youtube.com/watch?v=9cnEnRADDLo

 

Mazzetta, J., Caudle, D., & Wadeneck, B. (n.d.). Digital Camera Imaging Evaluation.

Retrieved march 3, 2015 from http://www.electrooptical.com/pdf/EOI%20OSG%202005%20Paper%20final.pdf

 

Rockwell, K. (n.d.). Nikon 50mm Lens Comparison.

Retrieved march 3, 2015 from http://www.kenrockwell.com/nikon/50-comparison/f-stops.htm

 

Clark, R. (April 20, 2014). Does Gear Matter in Photography? Clarkvision, 1(2).

Retrieved march 9, 2015 from http://www.clarkvision.com/articles/does.gear.matter/index.html

Comment

This post doesn't have any comment. Be the first one!

hide comments
ShareTw.Fb.Pin.
...

This is a unique website which will require a more modern browser to work!

Please upgrade today!