What is HDR and the difference from latitude?

Overview

I had the chance to look into HDR (High Dynamic Range), a term used in photography, so I'll briefly summarize it in this article. I did not know that HDR was also used in the audio field.

Google Trends on HDR

The spikes in the graph likely correspond to when the HDR feature was added to iPhone cameras, or perhaps when High-dynamic-range rendering gained popularity.

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The Meaning of HDR

HDR stands for High Dynamic Range.

It has mainly been known as a term in photography, video, and camera fields. However, as I researched it, I found out that HDR is also used in the audio field. I actually got to know this, so a bit surprising to me.

The Difference Between HDR and Latitude

Before explaining HDR, I will briefly introduce the term "latitude."

Latitude, in English, means "geographical latitude" and is also a term often heard in software or libraries dealing with maps. Generally, in English, "latitude" refers to geographical latitude.

On the other hand, latitude is also a term used in photography. In English, it's simply called "latitude," but in the context of photography, it is referred to as "exposure latitude," which means the range of exposure a camera can handle.

In photography, latitude refers to the range of tonal gradation that can express light and dark. This term is used for both film cameras and digital camera image sensors, but it seems to have been used primarily during the era of film cameras. Over time, the term "latitude" has gradually been replaced by "dynamic range."

I remember learning the word latitude from a photographer I worked with sometime between 2007 and 2010. I also recall hearing about HDR at that time.

In Canon's photography glossary, it is explained as follows:

Latitude refers to the range of brightness from light to dark that can be captured by film used in silver halide cameras. Areas beyond this range will result in overexposure (white-out) or underexposure (black-out). In digital cameras, this range is referred to as dynamic range.

Source: Latitude - Photography Glossary: Special Features | Canon (https://personal.canon.jp/articles/beginner/glossary/latitude)

What is HDR?

HDR, or High Dynamic Range, in the field of cameras and video, often refers to the function of capturing a wider range of brightness in an image or video.

Here is a quote about HDR photography from Canon’s photography glossary:

HDR (High Dynamic Range) photography, which is effective when there are large differences in brightness Even though it may look beautiful to the eye, after taking a photo, the sky might turn completely white, or conversely, the sky may appear fine, but the ground turns completely dark. This is what is known as overexposure (white-out) or underexposure (black-out). The reason for this is that the camera cannot capture the entire range of brightness.

The range of brightness that a camera can capture is called dynamic range. HDR photography is a function that allows you to capture bright and dark areas even when there is a significant difference in brightness. HDR photography refers to High Dynamic Range photography, where multiple photos with different brightness levels are taken, and these are combined within the camera, smartphone, or RAW processing software to create an image with a broader range of brightness.

Source: HDR - Photography Glossary: Special Features | Canon (https://personal.canon.jp/articles/beginner/glossary/hdr)

Thus, rather than a scale for light and dark, HDR can be seen as a function for expressing both light and dark gradations in an image with high contrast. Therefore, instead of just calling it "HDR," it feels more appropriate to say "HDR function" or "HDR photography."

In digital cameras and smartphone cameras with an HDR function, multiple photos with different brightness levels are taken and combined, allowing for the expression of gradations of brightness that cannot be captured in a single image.

This function is particularly beneficial in situations like extremely bright daylight, nightscapes, or nighttime portrait photography. Some people may have experienced the phenomenon where the brightness unexpectedly changes depending on where the camera focuses. HDR photography addresses this issue.

While it's now easy to take HDR photos on smartphones, in the past, the compositing process, which is now handled by the smartphone or digital camera, was also done using Photoshop. Of course, Photoshop's photo editing is not just for HDR editing but also serves as an intentional design technique.

HDR from the Viewer’s Perspective

Next, let’s talk a little about the devices that display HDR content.

For example, if you play a video shot with a 4K-compatible camera on a CRT TV or a feature phone, the beauty of 4K will not be displayed, right?

In other words, even if data is shot with the highest quality, it’s meaningless unless the device displaying it has the ability to show that high-quality data.

From the viewer’s perspective, monitors and displays that can show a wider range of color and brightness gradation are being sold. There also seems to be some standards for this.

HDR in Audio

It seems that HDR is also used in audio, sometimes referred to as HDR audio. It appears to be a technology to widen the range of sounds that can be expressed. I’m still studying whether there’s a difference between HDR audio and high-resolution audio.

HDR in the Web - AVIF and WebP

What prompted me to research HDR again was the next-generation image format AVIF (AV1 Image File Format).

Until now, I thought the next-generation image format would be WebP, but after learning about AVIF and hearing the news that Google now supports AVIF images in search results, I decided to look into it.

Reference Google検索がAVIF画像フォーマットをサポート

Since AVIF supports HDR, I researched HDR again and created this article.

What surprised me even more was the difference in gradient representation between AVIF and WebP images, as shown in articles comparing the two.

It seems that WebP is weak in representing gradients when the image quality is lowered.

This was new for me.

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In Conclusion

Image quality and formats continue to evolve rapidly.

However, I wonder how many people can actually view photos and videos taken with the best cameras at 100% of their quality. As you know, it depends on the display they are using, and not everyone has a high-quality display.

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