Having great hardware helps with the tuning because it transmits better information to the camera app. For big sensors, the signal is better for noise and texture. But its shallow depth of field makes it harder to tune the autofocus. Tuning teams therefore face contradictory objectives. Will they put more effort into focus performance or texture/noise ratio?

The FX0808 light is part of the Ai “Expandable Series” of lights.  This enables our team to build a light of this type from 1” x 1” (25 x 25 mm) to 24” x 24” (610 x 610 mm) in 1” (25 mm) increments, all available in 2 weeks.

It’s also important to pair the lens focal length correctly in order to prevent vignetting, or “port-holing” – which is particularly true of the Diffuse Dome Light.

As an experienced scientific tester of smartphones, DXOMARK is in a unique position to measure how well a device’s cameras, audio, display, and battery perform through its rigorous protocols that assess the user’s experience. What we see every day is that tuning is the critical step in finding the right balance between software and hardware interaction so that the user can benefit from all of the device’s features. Striking that optimization balance is often an art that involves strategic choices on the part of the phone manufacturer.

Earlier this year, DXOMARK introduced its Decodes series, which aims to explain concepts or dispel myths related to technology, particularly in smartphones and other consumer electronics.

Let’s look at the effect of tuning and sensor size on low-light performance. To do so, we selected ultra-premium (>800€) smartphones launched since 2022. The key image quality attributes are texture and noise. Here, we narrowed the analysis to the scores in low-light conditions.

Let’s view images from samples that illustrate the advantages of applying the Flat Diffuse Light versus other diffuse lights, including a Diffuse Dome Light and a Square Coaxial Light.

Modern smartphones use bright lenses, with an aperture often under f/2.0. This, in combination with big sensors, produces a shallow depth of field, which is the range of distance in which a person or an object is in focus. The deeper the depth of field, the easier it is for the phone to find the right focus plan. This might affect autofocus stability.

Diffuse lightexample

For example, Apple has doubled the size of the light-sensitive surface between the iPhone 12 Pro Max and iPhone 15 Pro Max, which corresponds to a gain of one stop. If we look at the flagship smartphone cameras released in 2023, the Oppo Find X6 Pro also has double the area compared to the iPhone 15 Pro Max, which corresponds also to one stop.

Another typically challenging part to illuminate effectively is the biomedical culture or sample titer tray. These parts are often presented on a tray with a matrix of regularly spaced wells of varying size and depth. In this particular example, the wells are relatively small (5 mm wide) and shallow (3 mm deep), and spaced at approximately 8 mm in X and Y. Additionally, each well has a laser-etched 2-D matrix code that must be read and verified by a vision system as part of an FDA-requirement for sample correlation and tracking history.

Figure 4 illustrates the limited size application of the 2”x2” Square Coaxial Light, where large size and set working distance are critical.

Diffuse lightCeiling

2) to maintain a high solid angle for even light distribution over curved or topographic surfaces, the low angle component from the dome interior must also be incident on the surface.

Advanced illumination offers a diffuse source to address the application shortcomings of other diffuse, bright field lights: the FX0808 Flat Diffuse Light and FD0808 Back-lit Flat Diffuse Light.  These Flat Diffuse Lights are a highly diffuse source with a viewing port in the center, allowing it to be used as front, or projection light (Figure 2).

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We also see that this short working distance contributes to an effective lighting geometry.  However, this is not an efficient sampling strategy, as the 75 x 125 mm tray would require multiple X & Y traverses to inspect the entire tray.

To maintain sufficient incident light intensity, uniformity, and angular distribution, Diffuse Lights are best placed close to the intended inspection surface.  This is particularly crucial for the Diffuse Dome Light for two reasons:

Low-light photography and videography are where we generally see the biggest gap in quality between small sensors and big sensors. Big sensors have a larger surface exposed to light, allowing them to capture more photons. More photons mean more signal, even in low light. Hence, all things being equal, increasing the size of the sensor enables better low-light performance. Night photography is a situation where having a large sensor can help with image quality.

Diffused lighting living room

It’s not difficult to imagine that a high solid angle light can become an increasingly lower solid angle and less intense light (inverse square rule) as the working distance is increased, effectively turning it into a more directional point source!

Some smartphone makers, such as Honor, Oppo, Vivo, and Xiaomi, have recently touted their use of big sensors, the so-called “1-inch sensor,” in their smartphone cameras. But does a big sensor alone help to improve image quality?

For example, attempting to improve both texture and noise in low-light conditions is particularly challenging because they usually work against each other.

Big sensors in smartphone cameras can provide some significant advantages in some situations such as low-light photography. But they are not the only answer. Smart and properly tuned software can sometimes compensate for a smaller sensor. All things being equal, a big sensor comes with challenges for other situations such as depth of field management. Proper tuning is essential more than ever if a device is to fully benefit from its performant hardware. So when it comes to image quality, a bigger sensor is not always better!

The image depicted in Figure 6E demonstrates that the DL097 Diffuse Dome Light effectively illuminates the tray at longer working distances.  But for larger sampling areas, we still require larger domes, which can be bulky, expensive, and may require longer lead times.

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While the Diffuse Dome Light is very effective on specular, curved, and topographic surfaces, and the Coaxial Light is effective for specular, flat, and angled surfaces of varying heights, both techniques have very specific application criteria that can present a challenge under some lighting circumstances.

As discussed in our previous Lighting Education Blog Post, diffuse lighting in machine vision applications may be classified as full bright field illumination as opposed to partial, or directional bright field lighting.  The underlying concept behind full bright field illumination, defined as illumination with a larger “solid angle”, is that light is sourced from a large area and is incident on the object surface from multiple angles (Figure 1A).

Diffuse lightin computer graphics

Surfaces prone to uneven reflectivity are often challenging to inspect – particularly with bright-field point sources commonly used in machine vision systems.  To achieve more uniform contrast over such surfaces, one solution is to apply diffuse lighting techniques.

Another thing to keep in mind is that a large sensor does not necessarily mean a higher pixel count, or better resolution. While a large sensor has the space to accommodate more pixels, a small sensor could contain the same amount of pixels as a large sensor. What could affect image quality would be the size of the pixels on the sensor. And that’s a company’s strategic choice between the desired resolution and image quality, because the smaller the pixel, the lower the signal-to-noise ratio, and therefore the lower resulting quality.

There are clever ways to optimize a device to get better image results. Tuning is the art of making the best out of all the image-processing algorithms available. These algorithms are found in the Image Signal Processing (ISP) chip or the camera app code. It is very much like cooking: It requires many tries and fails to find the perfect recipe. There is one recipe for each type of scene.

For illustration purposes, we can see the 2-D matrix code in close-up views (See Figures 5A–5D).  A 2” (50 mm) working distance is necessary for the code to be read and verified with a standard resolution CCD camera, while also being typical of the working distances required for effective diffuse and coaxial source lighting.

Big sensors on the other hand, can beat these numbers both for texture and noise. To date, two 1-inch sensor smartphones are the best devices in low light. They reached the two top spots in both low-light texture and noise categories under our DXOMARK Camera v5 test protocol. However, using a big sensor does not remove the necessity of putting some efforts into algorithms and tuning. We see that because some other devices with large sensors are low in both texture and noise, with scores under 80.

PCBs can be challenging to illuminate correctly, particularly those with large or odd-shaped components, like capacitors or heat sinks. Figures 3A-3D illustrate the differences among the three diffuse lighting options: dome, flat, and coaxial.

Diffuse lightvs directlight

In this article, we’ll touch on some of the advantages as well as the disadvantages of having a large sensor in your smartphone. We’ll also take a look at the shooting scenarios that benefit from a large sensor, which could explain the trend toward larger sensors in smartphone cameras.

Many smartphone users often express their frustration with their low-light pictures and videos. A key area for improvement for all smartphone cameras continues to be low-light performance.

Diffused lighting interior design

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First, what we call a 1-inch sensor does not really refer to a sensor that measures 1-inch. The history of the term is linked to the days when video was shot through tubes that measured 1-inch in outside diameter and had a diagonal of 16mm. This number should be read as the equivalent for a 1- inch video camera tube. Manufacturers’ phone specifications often express the sensor sizes as a fraction of a 1-inch video camera tube.

Diffusedlightphotography

Earlier this year we focused on the importance of software tuning to the display experience. In this latest installment of our series, we’ll try to decode how a large main camera sensor affects the image quality of the device’s photos.

Figure 7A illustrates the entire tray lighted using the FX0808 Flat Diffuse Light at a 12” (305 mm) working distance.  In conjunction with a high-resolution CCD or CMOS camera, the FX0808 provides for a very robust and efficient inspection solution for larger fields of view.

We observed that small sensors, in general, present a limit in terms of texture and noise score compromise. On the graph below, which includes the scores of some of the best devices from 2022 to 2023, it can go as high as 104 points for the noise score and 97 points for the texture score.

Diffuse lightbulb

Specifically, as illustrated in Fig 1A, a Diffuse Dome Light illuminates from nearly an entire hemisphere; hence it is described as having a relatively larger “solid angle”  than the directional Spot Light depicted in Figure 1B.

Over the past years, smartphone manufacturers have been increasing the size of the sensor to improve the sensitivity to light.

In the days of film photography, the only option for photographers to combat low-light challenges was to extend the capture time. But they faced the risk of generating motion blur if the subject was moving or if the photographer was holding the camera. In digital photography, the answer to combating low-light challenges is found in reaching a good balance between texture (detail) and noise. Small sensors often produce a lower texture/noise ratio in the final images. Big sensors are a great tool to improve this ratio.

On the other hand, while a big sensor paired with a lens with a large aperture could be ideal for portraits and low-light images, it might not be ideal for photos where a large depth of field is needed, such as landscape photography or group portraits.

If we instead apply the same lighting schemes to a longer working distance view (Figures 6A-6E & 7A), one that may only require 1-2 image frames per tray, we see that only the Flat Diffuse Light and the DL097 Diffuse Dome Light are effective (Figures 6D & 6E, respectively).  Of course, a much higher resolution camera would be necessary to resolve the 2-D laser etched codes.

We see that the Diffuse Dome Light and Flat Diffuse Light work equally well for relatively small areas of the PCB (Figures 3A & 3B).  In comparison, the large Diffuse Dome is less effective than the Flat Diffuse Light on larger fields-of-view, primarily because the dome has to be oversized by at least 50% of the intended field-of-view size (Figures 3C & 3D).

Some manufacturers, however,  do not specify the smartphone camera’s sensor size, but if the number of pixels is known as well as the size of the pixels, it is possible to estimate the sensor size. For example, for  a camera with 48 MP and pixel size of 1.22 µm, the formula to estimate the sensor size is 48 MP x 1.22 µm x 1.22 µm = 71.44 mm² (sensor area.)