Cameras vs. Image Quality: Megapixel resolution is not the aspect that contributes the most

I have received as more questions about camera choice on smartphones as more people know that I do photography and what I am studying is also related to images (medical images and digital data analysis, to be exact). The more I discuss with them, the more interesting I find that we are often manipulated a lot by product marketing campaigns and the biased opinions of many people, from high-end/professional photographers to amateurs, of what is advertised and what is really applied in practice. Listening is a good skill to practice, and having different opinions from different people is such a good thing, but we need to keep our mind clear in the era of information blooming. The most frequently asked question is that whether higher resolution cameras (denoted by the number of mega pixels) should give better photos. "a BIG NO NO!" would be my first reaction. Even though resolution does contribute to the quality of photos, but the impact is really small and that is not the whole story. There are several (not that many, in fact) other aspects that are way more important and worth noting. I also do understand that the perception of beauty (that we relate to "quality") varies from person to person. I don't want and can't put beauty standard from industry, art, science or whatever, even from my own, on you through this writing. I just want to make clear some photography terms that are misused by media and misunderstood by the public. From there, I hope that you can have a better look at what is going on in this manipulated world, and facilitate your searching and decision making processes.

I believe that some marketers or sellers will be upset if they read this post as what I point out here is not beneficial to their business. You don't support this post, what do I say then? It's forever ever impossible to please everyone, and at all times. The post here aims to bring out the topic that we usually face in daily life but apparently lots of us still don't have a proper look at it. I propose and suggest ideas, also hope to receive your constructive comments or even debates. If you can't find anything fruitful after reading or even get mad about it, f*** off and move on :).

Enough for forewords, let's dive in.

The impact factors on image quality:

Sensor size
Lens
Resolution
Compression
Techniques
Brands

where the first 2 factors have the most impact in the aspect of hardware design. These factors contribute greatly to your buying decision on which type of camera that suits your needs.

1. Sensor size

From Fig. 1-2, you will see that image sensors on phones are of the smallest size among common camera types that you usually see in daily life or on the market (added info: action/sport cameras, for example GoPro, have 1/2.3" (1), still a little bigger than phones). The bigger the sensor is, the better the camera captures lights. In other words, larger sensors allow each pixel to have larger effective area in order to achieve higher light sensitivity with lower image noise. This is super important for low light conditions such as taking photos at night.

Figure 1: Camera Sensor size comparison chart.

Figure 2: Image sensor format, size comparison.

In good lighting condition like daylight or studio light setup, phone cameras produce nearly as good photos as stand-alone cameras do despite of having much smaller sensor size. This is because digital sensors handle well lighted scenes much better than low lighted ones, and there is less noise related issue in bright and well exposed scenes, as shown in Fig. 3. Noise in low light mainly comes from electronic components. We tend to use higher sensitivity (ISO) to capture weak signals (low lighted details) but at the sae time, amplify unwanted signals (noise) (Fig. 4).

Figure 3: Higher ISO, higher noise to deal with.

Figure 4: Noise appears more as ISO increases.

Obviously, larger sensors allow to reach higher resolutions (denoted as a number in mega pixels - MP). Size does matter, you already know it ;), but not in all contexts. In section 3, we will talk more about image resolution, which will show us how less likely higher resolutions give better quality. Beside resolution, larger sensors have wider dynamic range, shallower depth of field, ability to use wider angle lens, etc. In contrast, investing in the heart of camera device comes with a price, I meant, real money $_$. Larger sensors definitely cost more, if I don't want to say it a lot more. Not only does the cost come from the increased physical size, but also power consumption, image processor and storage, and all other supporting components to make sure that the whole system is compatible and runs seamlessly.

In short, by considering only the quality, sensors on stand-alone cameras perform better than on compact cameras, and on phones is the worst among 3.

2. Lens

Being able to change a lens is the most powerful ability on stand-alone cameras, compared to phone cameras. Lenses open a lot of new possibility for the photographer's creation. Of course, not everyone likes taking photos, and not all photo-taking lovers are photographers (at least, to what they want to address themselves), and even more, not all photographers are fully equipped. It all comes with a proper question: What do you want to do with your photography journey? You should only equip yourself with what you need to meet your desire. You have no idea yet? Get the basic gear, then ideas will come from time to time you use it. Remember what I just told you? Need. Your NEED! You buy things to serve your needs, not how much money you can afford, and not how much cheap products are, even if they are. Get it enough, save money, reduce waste, preserve nature and our mother Earth for the future of our next generationsss.... Oops sorry, I've just gone too far off topic, but you get what I mean, right? :)

Figure 5: Lens set for stand-alone cameras.

The lens changing explains why modern smartphones have more than one camera, as shown in Fig. 6. Added cameras serve as a boost up in the race of keeping up with stand-alone cameras' photo-taking abilities. Beside one main camera, other cameras are designed to go with different lenses for specific functions such as tele-zoom, wide-angle, detail-enhanced photos, depth of field estimation. The new age has come (as it always does :) ), with the development of Augmented Reality (AR) technology, more cameras help increase the user's experience on his/her multi-task phone.

Figure 6: Multiple cameras on modern smartphones.

Moreover, image quality depends a lot on lens optical quality, as being concerned by optical phenomena like diffraction, refraction, diffusion, reflection, just to name a few. With high quality made lenses, lights can pass through and end up properly on the image sensor so that all details are retained from the illuminated subject. Details here are not just simply about brightness, but also contrast, color & chromatic aberrations, image distortion, so on. Even though built-in lenses are already of quality to match with phone cameras, and the same goes for stand-alone cameras, there are still more or less quality range between lens manufacturers. Hence, having the possibility to choose lenses for one's own use is preferred, especially for high-end users with their perfection vision going beyond my capability.

In short, high quality lenses and changing option belong to the group of stand-alone cameras, which helps produce better images.

3. Resolution

Oh yes, finally here is the section you would love to take a look at, after the first two that you may find not relating to your interests. Unfortunately, I personally don't appreciate this factor and therefore, will not write too much about it. Higher resolution is better, what an obvious statement, right? Yes and no. Again, I say that it depends on your need, which is not easy to find out (probably you question yourself about your existence in this life or the meaning of your life more than what you want or need for camera selection :) ), but also not too difficult. For your information, the highest resolution on phones [on the market, up to 2020] is 108 MP., while on stand-alone cameras is 50 MP. A research from Dr. Roger Clark shows that human eye has the resolution of 576 MP. ~how amazinggg~

More specifically, high resolutions would be favorable for printing or editing purpose mostly. Otherwise, sticking with average resolution, like 5 or 8 MP, is more than needed in most cases, in terms of storage and display. The proposed idea is to use no more resolution than it can be properly displayed. Take a look at Fig. 7 and 8 for pixel size equivalent resolutions and standard display resolutions. At 3 MP., the image size (2048x1536) can already fit a Full HD display (1920x1080), whose resolution is a norm nowadays. For printing purpose at industry standard 300 dpi., it can fill the paper size of 6.8"x5.1" (to compare, A4 paper is 8.3"x11.7", a postal letter is approximately 3.5"x5.5").

Figure 7: Pixel size equivelent to the resolution.

Another purpose for using higher resolutions is cropping, which suits those who love editing (post processing). You can partially crop the image, to certain degree, without losing any details (no interpolation scaling up). Digital zooming is what I don't like much but high resolutions allow to zoom in (pinch open on the phone screen) to certain degrees that preserve details (instead of interpolated pixels, which is the worst case for quality maintainance).

Going back to phone cameras, nowadays it's quite easy to find an affordable phone with a 12 MP. camera on the market. Even more, 48 MP. camera is widely advertised as the new cutting edge for photo experience. However, in practice, I rarely need to use that resolution. In fact, the 48 MP. feature on my phone (Redmi Note 7) is just an option, and 12 MP. is set by default instead. It turns out that the 48 MP. sensor is rather used for enhancing details in the scaled down 12 MP. photos. 4 times more pixels should lead to bigger sensor; however, the actual design is that the physical size is originally kept and pixel size is now reduced 4 times. This is a good move for space design, but not for photo quality. As the sensor size is already small on the phone, reducing pixel size does not help improve image quality overall. Particularly, daylight photos may be improved but night photos are worse due to the light sensitivity reduction and noise sensitivity augmentation on each pixel.

Figure: A close up appearance of image sensor.

Things change quickly on camera market, especially smartphone cameras. It's gone for long time the epoch where every megapixel counts on the market competition. At the time of this writing, AI camera is a thing now. Hardware improvement has been slowing down, and software added value is now the real weapon race between big companies.

4. Compression

Compression is meant to reduce size for storage space, which is always a limited resource. By applying compression, we have to lose some data (except lossless methods), which should be redundant and less important, as a trade-off. We have a lot of available compression formats but here, we are interested only in the commonly used JPEG, a lossy compression (even though we have other lossless image compressions) to compare with RAW, a non processed format that is out of sensor without a touch from image processor, which can be understood as non, lossless or very low loss data compression.

An ordinary user wouldn't need to use RAW format as it requires more work to be done before having the photo ready to publish, that is printing or displaying. However, if used, RAW format gives you more ability to edit, and therefore, the final output image will be more stunning. One of the advantages that I like the most is the ability to recover details in super dark or burn bright areas, which can't be done properly on JPEG, as shown in Fig. 9. Other advantages are wider color range encoder, non destructive editing, finer control over adjustments (white balance, color saturation, brightness, contrast, sharpness, etc.) (Fig. 10), and so on. With non-destructive approach, you don't have to deal with compression artifacts (distortion) in JPEG during editing.

Figure 9: Detail recovering in shadow and bright burn area on RAW format.

Figure 10: Color enhancement and detail restoration on RAW.

However, there are always drawbacks, which should be considered whether you really can accept or not. Firstly, the storage size is much larger, from 2 to 6 times. For example, my Canon 700D (18 MP.) produces 5-6 MB JPEG photos and 20-23 MB RAW, while my Redmi Note 7 (12 MP. setup) does similarly. The shortage of storage can be avoided easily nowadays thanks to the more affordable price of external drives and storage cards. Besides, large file size can also affect shooting speed in burst mode as writing data to memory takes more time for each shot. Secondly, RAW is a not ready-to-use image, which means it takes extra steps, that is more time and effort to process and export images. Tbl. 1 summarizes the main points of comparison.

Most stand-alone cameras allow users to set whether they want to produce images under JPEG, RAW or even both. On phones, the default camera app only allows JPEG export (except high-end phones). If you want to keep RAW, you have to install a third party camera app, like Camera X on Android.

5. Techniques

At this point, we start to get out of camera hardware dependence. The photo quality definition slightly changes from hardware made to human. In other words, the quality is now dependent on how well we control the camera to make use of its capability and on scene setup. That is to say, a high-end camera in a carelessly shaky hand won't make any sharp photos. A full-frame camera still makes noisy photos if the user uses it in an extremely poor light condition that is out of camera's reach. A shot of racing car still can be all blurry if the cameraman doesn't use tripod or other techniques to stabilize. RAW can't retrieve lost pixels in too dark zone, like barely any light from the subject. Photos may be unpleasant to look at due to bad framing or lack of light setup.

There are so many techniques and its variants adapted to the photographer's ability. As a result, it's quite out of scope of this post, so I hope to write it another time, in another post, or probably in a book :).

Figure 11: Behind the scene a photoshoot.

6. Camera brands

Hell no, I'm not going to show you which brand to buy, which one is better than another or things like that partly because I don't really have enough experiences of using different brands, partly because I value techniques and creative scene setup to create good photos more than camera hardware itself. However, for a starting point, each brand has its product range and competitive prices. Accessories are also something worth looking at.

Conclusion

I've talked a lot about camera specifications, optics and software so that you can have a better understanding of the relation between camera devices and image quality. With that in mind, I hope you can find for yourself a suitable camera for a great photography journey to come, even if you don't intend to do so. However, what comes to the final decision is usually the most simple factor: budget. After knowing what you need and all possibilities, the remaining question is to maximize what you can get from your current budget. Take your time to think about it, make up your mind and there you go. Everyone has to start at a certain point to grow up in their life experience. Good luck, and have fun photographing!

Notes

(1) sizes expressed in inches mean video camera tube equivalency sizes (optical format), not the actual physical size unless explicitly described in mm.

Figure source

[1] capturetheatlas.com

[2] Image sensor format, wikipedia.

[3] www.exposureguide.com

[4] www.photographybay.com

[5] www.getolympus.com

[6, 9, 11] Internet

[7] photographychef.com

[8] wikipedia commons

[12] Lior Glaichman, petapixel.com