Optical Zoom vs Digital Zoom – What’s the Difference?

Optical Zoom vs Digital Zoom

When I went to Japan, I brought up my iPhone and Android phone. These were essentially my main cameras for the trip. They served me well for the most part.

Many of the photos that I’ve taken were wide-angle shots, considering the landscape, cityscape and street photos that I taken. Having said that, there come times where you wish you could zoom further and get close to the subject. Like it was in the Sumo tournament in Osaka, Japan.

Of course, one option is just to get closer on foot. Although this might serve you well at times, it won’t help you get a subject. A subject that is either unreachable (e.g. a lion in the zoo), at a higher place (e.g. Big Bang clock), far away from you (e.g. soccer player shot from the upper place), and in a cage (e.g. shooting through a fence).

The Problem with Digital Zoom

I do have digital zoom. Most phone cameras and consumer digital cameras have that. The problem is with digital zoom is that what it does it cut the image and enlarge it to make the subject larger. The image data information doesn’t change. If you enlarge an image to a larger size and either use the same amount of pixels or less (less in the case of cropping the image), you get a blurry image.

Why it’s blurry because the image enlargement interpolation needs to add pixels. It puts data that wasn’t actually there in the first place. The enlargement algorithm can feel in the gap a nice way, but the original image data won’t magically appear in the image. If you make a little digital zoom it might not be so noticeable. However, as you use a higher zoom, the image will become significantly blurry.

Why We Need a Digital Zoom at All?

So why use Digital Zoom in the first place?  It’s simple, it just makes it easier for amateur photographers to frame their shot instead of using a photo editing app to do so.

It’s important to note that you can still crop the image in-camera or photo editing app without enlargement. This is, of course, the best way to go, because you don’t impair the image quality. One problem is that depends on the cropping size, the resolution of the cropped image might be too small. Second, if the camera doesn’t capture a very sharp image, making a crop and letting people watch it in full size might expose the lack of sharpness or other optical artifacts in the image.

For example, if I have a 48MP very sharp high-quality image. I can just crop it even to 6MP anywhere in the image and still get a fantastic looking image.

You might say, OK, I can enlarge the image but always reduce its size later on. Keep in mind, that resizing always lead to loss of image information, because you manipulate artificially injected pixels, so it’s a “lossy” process not “lossless”.

Why Can’t We Have a Cropping Option (No enlargement)?

The next question that you might ask? Why we don’t have this option for just cropping the image on mobile phones as a “crop zoom” option?

Well, many camera apps do offer the option to edit and crop the image, but indeed, many camera apps don’t have this feature. If you have a smartphone with a very high-resolution sensor, or with any resolution in that aspect, give users an option in the menu to decide how the artificial zoom will work, whether it’s ‘only cropping’, or ‘crop and enlarge’.

Maybe some phones do that, but I am sure there are third-party camera apps that do that. My phone doesn’t.

Sharing Low-resolution Images on Social Media

There is another thing. Most of the people won’t share a higher resolution image, but upload their images to social networks where the image size is reduced and further optimized for displaying it on mobile and on the web.

Think about it. Would you prefer waiting for a single 5-megabyte sized image to download when you can get the same viewing experience on your mobile phone viewing a 300-Kilobyte image?

So eventually, most pictures are downscaled and optimized for web viewing. This means that the artifacts, lack of sharpness and other issues that you see when viewing the image at 100% scale won’t be that noticeable when viewing on the web on a smaller scale.

Digital Zoom Image Loss Examples

OK, enough talking, let me give you some examples.

Digital Zoom Example 1
Very little digital zoom used

In the image above, very little digital zoom used. Look at the people’s faces, they still look quite good.

Now let’s take a look at an image with a much higher digital zoom.

Digital zoom example 2
A much higher digital zoom

As you can see, the details in the second image when viewed at 100% scale (the circle represents a 100% scale crop), the second image is much more blurry and lack of details.

By the way, both images were shot at 4608 x 2176 pixels on my OnePlus 6 mobile phone.

However, although the second image looks very blurry and lack of detail in 100%, it looks fine scaled down. Yes, how you see it embedded in this blog post or even if you tap it and view it in the gallery widget, it will still look quite good. This is because you don’t view it in 100% scale.

The thing is that the more you increase the digital zoom, the worse the image will become. But even with a scaled-down image, you can still see that it’s not sharp. It’s good for web viewing.

Crop vs Crop & Enlargement

Now let’s take the first image, which is relatively sharp and try to apply a “digital zoom” (image enlargement in Photoshop) versus just cropping and see the difference. The output will be the same frame in the image, but on is cropped from the original, the other one is cropped and enlarged.

There are two images here. Left one is just a crop from the original (tap it an view it). The second one is crop and enlargement so the height matches the original height of the original image.

When you look at it scaled-down, you can barely notice the difference. Try viewing both images at 100% (tap and hold and open it in a new tab then tap to view it in 100% scale on your mobile or desktop browser). The enlargement creates a bigger image but it looks very blurry. The cropped image remains as sharp as the original image and not blurry because it wasn’t stretched out.

AI-based Enlargement for Better Results

So although you get a high-resolution image, pixel-wise, you don’t get to see more details. There are some digital zoom algorithms that can do a fine job feeling in the gap, especially those who use Machine Learning algorithms for resizing images.

This is why we’ve seen things like AI-based zoom which uses machine learning to deliver better results. Still, the information is artificially generated. The results are better in general, and Machine Learning has the capability to feel in the gap in a way that it produced a much better-looking image. But again, it’s computing-intensive and those algorithms used in phones and digital cameras have their limit due to the processing limitation.

I do see phone companies offer an option for digital-zoom cloud processing. The image is sent to the cloud over the web, processed and downloaded after the Deep Learning algorithm was applied to it.

Many of the phones nowadays use several sensors. Phone manufacturers can use the secondary sensor used for artificial Bokeh reproduction alongside Machine Learning (ML) algorithms to further improve the digital zoom capability. Some of those secondary sensors are monochrome sensors, but the brightness data can be used to enhance the image alongside more advanced image computing algorithms.

So Should You Use Digital Zoom?

As you can clearly see, the trend on mobile phones right now is optical zoom or having several prime lenses offering different focal lengths. The phone can “stitch” those up and provide a smooth transition between the focal lengths. When I say optical zoom, I refer to the ability to actively zoom in on the subject. However, having two prime lenses and switching between the two lenses is a “zoom” function,  because it switching from one focal length to another.

Whether it’s continuous or not it doesn’t matter. We correlate the “zooming” word with a movement. But if you switch from a wide-angle lens to a telephoto lens on your phone, what you deed is you “Zoomed-in” on your subject, or “zoomed-out” if you do the opposite, moved from telephoto shooting angle to wide.

What digital zoom gives you is convenience. It feels in the gap between having a small cropped image than having a stretched image that can look “satisfying”  on various displays.

It depends on the resolution of the image. If you have a 48MP sensor like some phones have nowadays, there is no reason to enlarge the image. The information in the image is enough for providing a good viewing experience on most screens, even desktops, including retinas displays. But with lower resolution sensors, sharing, for example, a 500px cropped-only image might look small on the screen. A digital enlargement will fill that gap. The image might look blurry to some extent (depends on the digital zoom use) but overall it will give users better viewing experience.

Keep in mind that you can always make the “digital zoom” yourself by enlarging an image and cropping it using photo editing apps. What the camera does when it’s digitally zooming in can be done using almost any photo editing app/software out there.

Summary

As you can see, the digital zoom has its pros and cons. Nowadays with phones featuring several cameras, including telephoto lenses, this issue of digital zoom might not be an issue in the future at all. People will have phones equipped with either continuous optical zoom cameras or several primes lenses that will give them the option to get closer to the subject without any image quality compromise that affects digital zoom.

I also used digital zoom myself., because I didn’t want to crop every image that I take before I share it on social media like on Instagram, Facebook, etc. Digital zoom was like a quick edit feature that is convenient to use for image sharing on social media.

Of course, when I view those images on my desktop and inspect them closely, they look bad. It all depends on what you want to do with your images. If you want to print them in high-quality, share them on Instagram or Whatsapp, create high-quality photos for your blog, etc.

Now that I own a DSLR camera, I don’t need to do that. Even with mobile phones featuring longer focal-length lenses, some of those don’t have the reach that I need, let along with the ability to achieve a shallow depth of field effect (Bokeh; Bokeh actually refer to the quality of the background blur, but most people relate it to just the blurring).

I can write more about this topic, but I think it’s a good place to stop. Whether you use digital zoom is up to you now that you know the advantages and disadvantages. If you can buy a phone with a telephoto lens, do it because then you won’t need to use the digital zoom. Or, you’ll use it, but the negative effect will be less prominent because you are already zoomed in quite highly on the subject.

Thanks for reading and enjoy taking pictures!

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