More Megapixels, More Image Quality?

We have experienced the increase of the megapixels on digital cameras during the past few years, I still remember when 0.5 megapixels was the largest image size we could find meanwhile nowadays we can find cameras with 24.3 megapixels and the megapixels will continue to increase as the camera companies keep telling users that largest megapixels translate in better image quality. Personally, as an amateur photographer and researcher in the field of image processing, I think that most of the time an image with more than 6 megapixels is a waste of memory and camera resources.

Let me start explaining the reasoning camera makers use to convince user that more megapixels is better: Printing quality. As you know, a good printing quality is achieved when the printing resolution is equal or higher than 300 PPI (pixels per inch) and, therefore, if you want to print a large image with good quality you would need to have a large image, for example with a 2 megapixels image the largest print size at 300 PPI would be of 14.7 cm x 9.7 cm (5.8” x 3.8”). You can do the math yourself, but in the page of Imagine 123 you will find a table of the image size and printing sizes you may have. The camera makers tell users that with larger pixels they won’t just be able to print in larger format but also they will obtain more detailed photographs since you will have more pixels to represent the objects in the image. I don’t say this claim is completely false, but you need to consider other aspects that aren’t as straightforward as the concept “bigger is better” and this discussion has been in the air since some years ago as you can see in this cnet news note from 2007.
If we accept as a fact that most photography enthusiasts don’t print their photos in large format, then the camera makers just have the detail in the image as the only reason to offer users more and more megapixels every day. But, it is really true that more megapixels are synonym of more detail? My answer is yes for just few cases but most of the times is a big no. Let me explain you my reasons:

First we need to consider the sensor of a digital camera, it is an array of light sensitive elements and each pixel will correspond to a small area of the sensor, meaning that the information in each pixel is the sum of the light arriving through the lenses into the pixel area. Now, if we keep the size of the sensor constant and we increase the megapixels the resulting pixel size will be reduced and therefore less light will arrive to each pixel increasing the effects of electrical noise in the sensor degrading not just the sensitivity to finer tonal gradations but also the quality of the image in dim conditions. As an example, I took two different photographs using my camera with 6 megapixels (2816 x 2112 pixels) and a 7.18 mm sensor and one of the cameras of the HORUS system with just 1 megapixel (1024 x 768 pixels) but a 8 mm sensor, i.e., more than twice larger pixels. You can see how there is more noise in the image captured with the 6 megapixels camera despite the fact that there are more pixels to represent the same object. You can see the complete pictures in my blog.
My camera
HORUS system camera

The noise is not a problem in highly illuminated scenes, that’s one of the few cases were bigger is better, but for dim conditions the camera makers try to solve the problem using clever image processing methods, for example increasing the gain of the light sensor and using filtering algorithms to reduce the noise, most of the times reducing also the image size. As you can imagine, the image processing will end up with an altered image and for purists this could be a downside of using cameras with large megapixels.  
At the end, maybe professional photographers will fully exploit the advantages of large images, but we must keep in mind that the image quality is not completely determined by the megapixels of it, we also must take into account the camera’s optics (lenses) and especially the sensor’s size and sensitivity and, therefore, we shouldn’t trick ourselves into the “bigger is better” mantra of most of the camera makers and sellers.

2 thoughts on “More Megapixels, More Image Quality?

  1. I think that the pixel issue is a clear example of vendors trying to sell their stuff using a semingly important metric. Unless someone actually is an expert nobody knows how much pixels one needs to make a nice picture.What everybody does know is that more pixels=more detail never mind that after 6 megapixels (or somewhere around) it is impossible to distinguish details in a picture as you point out. However vendors still want to compete and put a simple metric as the main focus of this competition. This also happened with CPUs in which the clockspeed was hailed as the most important metric while ofcourse other metrics are equally or even more important.I believe this is a result of the human inability to weigh more options (lense quality, speed, sensitivity, memory etc..) so vendors focus on one simple to understand metric(pixels, speed etc.) even when it does not make much sense to do so for the quality of the product. I think this happens also elsewhere, but i lack examples 🙂 RegardsJurriën

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