Most people interested in digital cameras know what resolution means. In digital images, TV screens, phones, and computer monitors, resolution refers to the amount of detail that the screen produces. High resolution screens display more detail. In the world of TV 4k UHD is the current high resolution standard that is most widely available. The older standard called 1080p or FULL HD is a less detailed but still high enough resolution format for many devices like phones and smaller tablet computers.
It seems like consumers naturally want higher resolution devices because they know they deliver more details which translates into more life like visuals for movies and games. I’ve heard people claim that tons of resolution isn’t necessary, they may say that “12MP is enough” or something along those lines. Well, the people who say that are right and wrong at the same time.
In any image there are two kinds of “detail”. The first type of detail is structural detail. This refers to the physical shape of the object shown in the image. This could be anything, sand, water, people, etc. In theory more resolution means more structural details will be visible. This type of resolution is what photographers are talking about when they say “12 megapixels is good enough”. And they’re mostly correct. A 12MP image is about 4,000 x 3,000 pixels, and most prints will look “good enough” at 100 dots per inch. If we divide 4,000 and 3,000 by 100, we find that 12MP should be “good enough” for a 40″x30″ print which is indeed very large and for most people, beyond “good enough”.
For extremely high resolution prints 150-300 dots per inch may be used. But this level of detail is well beyond what would be considered visible to the human eye at typical viewing distances. So why would anyone ever want to print at such high resolutions??
It actually doesn’t have to do with structural details, but color details. What is color detail? Color detail is typically going to come across as the accuracy of color transitions. This would be things like the subtle color shifts on people’s skin, not just from lighting, but also from the skin itself.
So how does increasing resolution improve color detail? The more resolution there is the more “steps” of color that can be represented. Let’s take the following example picture of some flowers and look at it more closely…
Now lets zoom in a little…
As the image is zoomed in, one thing that starts to become clear is that details are actually made up of pixels. If I zoom in all the way to 800% this is what the screen now shows…
After zooming to 800% I can see the pixels that make up the image. This is a very high resolution 45 megapixel image so details are well represented as well as colors and subtle shading and gradients can be seen.
But what happens if I lower the resolution then zoom in? Let’s cut the whole image down to 12 megapixels and see what happens when we zoom in to the same magnification.
In the bottom 12 megapixel image the first thing I notice is that the pixels appear larger, and that is the effect of blowing up a lower resolution image to the same size of a higher resolution image. What we can do now is easily count the pixels in this area. Let’s count the pixels of the dark dot just left of the center blob. It appears to be about 4 pixels high and 3 pixels wide. How much color resolution is there in that spot? There’s 12 pixels of resolution which means the spot has less color definition in it. In the more detailed image the dot is about 9×9 pixels in size which corresponds to 81 pixels. Remember that 8-bit color corresponds to 256 grey levels per pixel. So, the color resolution of that dot in the lower resolution image is far, far below the standard even for 8-bit color. In other words, the lower resolution image can’t represent 8 bit color in the details. Does that matter? I don’t know, but if I spend a lot of money for a camera I would expect it to render details with some accuracy.
The point is that no matter how good a 12MP camera is, it can’t achieve as high a color depth as a higher resolution camera. There is no such thing as “better quality pixels” because pixels don’t really have a quality. A pixel represents a color value, and if there aren’t enough pixels in an area of the image to express the whole of the color then the “better quality pixels” don’t matter because the number of pixels needed to represent colors in the image just isn’t there.
300 DPI prints are a good example of this. Comparing a 100 DPI print to a 300 DPI print may make the 100 DPI print look as if it is “good enough” but close inspection will show that the color mixing and accuracy in the 300 DPI print will be better.
For video it’s a similar story. The higher the resolution, the more color values can be represented in a given area of detail. The difference for video is that since the image is always changing from frame to frame the human eye isn’t really able to make out fine color gradients in the details.
Are some camera companies being dishonest about the color depth?
There are a few camera’s out there that advertise 16 bit color depth. Well, 16 bit color is over 65,000 shades of color. 8 bit color is 256 shades. In order for an area of an image to have 16-bit color resolution it has to have a minimum (for one specific hue) of 65,536 pixels. That corresponds to a pixel area that is 256×256 pixels in size. Realistically that’s just for a black and white image. If there are multiple colors in an image than the number of pixels needed increases by 65,536 for every color present in the image. It’s not long before you realize that 16-bit color doesn’t exist in a 12 megapixel camera or a 45 megapixel camera, in fact, no cameras have that many pixels in them. 16-bit color equates to 281 trillion different colors which seems like more colors than my eyes could ever comprehend.
I’m guessing a printer that could deliver full 16-bit resolution would have about a billion different ink colors in it and would be as big as a small city.
Resolution doesn’t just deal with structural detail or “sharpness”, it is also intrinsically linked to color depth as well.