How is the N82’s ISO performance?

A camera and in this case a camera phone’s ISO performance is very important for low-light photography. As you may or may not know DSLR cameras are not only faster than conventional digital cameras and camera phones but are known for their excellent ISO performance. Digital imaging devices like cameras and camera phones use an ISO speed, a numeric representation of the camera’s sensitivity to light.  The higher the ISO speed, the higher the sensitivity to light is increased. This will allow you to shoot images in dark conditions without flash, creating more natural-looking night-time pictures. On top of that in some situations flash-photography might be prohibited, that’s why in those cases the higher ISO speed will allow you to shoot without flash while still allowing you to brighten the scene and prevent camera-shake. On the other hand increasing the ISO speed does not only have advantages, but is also brings its disadvantages like: Image noise. As the ISO value is increased it increases its sensitivity to light making full use of the available light, but at the same time the unwanted image noise is increased. This noise can be seen when you zoom into a picture and you would actually see small grains in the image.  On a camera with poor high ISO performance you would probably see these small grains without having to zoom in. This is one of those areas where DLSR cameras excel: they can increase the ISO speed to very high levels like ISO 1600 without getting images that are too grainy. Manufacturers don’t sit quietly either: in cases where the grain starts to become very obvious they apply “noise reduction”, basically trying to get rid of the grainy images. If they apply too much noise reduction, a lot of details will be lost; basically the image would look like water painting. At its most basic form this is like blurring an image to remove the noise, but a fine balance has to be found that will remove some noise, but not lose too much detail in the process.

Armed with the N82, I will be checking its ISO performance without the use of flash. The N82’s camera has 4 ISO settings: Auto, Low, Medium and High. Personally I don’t like this naming scheme as it doesn’t tell us anything about the ISO speed being used. The purpose of this test is to see if raising the ISO levels would affect the image by “brightening it up” and to see how much noise is introduced into the image. Is the noise level of ISO 400 a lot more then let’s say ISO 100? In this case I will not use “AUTO ISO” because in this mode the camera itself will choose the ISO mode, based on what it thinks is appropriate for the image.

Testing Method

To accomplish this test, full-size images were taken at the highest resolution and then cropped and zoomed in at a very close level.

The Results and Analysis (click to see full-size images)

 

Upon inspection of the Exif data we make a very important discovery: The “Low” ISO used in the N82’s software adheres to an ISO level of 100, the “Medium” to ISO 200 and “High” to ISO 400. Looking at the produced images we can see several things. First of all, with the increase of the ISO level the light levels increases. This is something that is expected, as increasing the ISO brightens up the image. Upon further inspection, another expected occurrence takes place: as the ISO rises “image noise” begins to get noticeable. In the first test this is visible on the letters “ER”. In the higher ISO level 400, you start to see that the white colors of the letters “ER” start to introduce more shades of white and grey and it starts to look more pixilated. In the second test you can see this in the black color surrounding the text: “TECH”. On the higher ISO level 400, the black is less of a solid black and has more shades of white and grey. Another thing that seems very obvious from the images is the fact that as Image Noise increases with ISO 200 and 400, we can see that Noise Reduction is applied. This can be seen on the red dot: noticed how the edges of the dot are much more blurred on ISO 200 and 400? And lastly in the ISO 400 images a lot of noise reduction is applied, but to make sure that image remains sharp they apply large amounts of edge enhancement also known as Sharpening.

Conclusion

Based on these two tests we can come to several conclusions:

-For a phone the N82 produces images that are amazingly clean making the gap between a mobile device and a stand-alone digital camera really small. 

-Nokia calls the ISO levels on the N82 Low, Medium and High. Inspection of the Exif data reveals that these adhere to ISO 100, 200 and 400 respectively.

-  As expected increasing the ISO on the N82, increases the Noise level. The noise levels in the higher settings are masked by excessive use of noise reduction. In the process of applying noise reduction there aren’t many details lost.

-Also expected is that increasing the ISO on the N82, the light levels increase, making the image brighter and making up for camera shake. The difference in light levels between ISO 200 and 400 is not that much different. The biggest difference comes from the fact that ISO 400 uses a lot more edge enhancement making things look crisper and bolder. In the end a lot of people might prefer the look of the image with ISO 400. On the other hand images done with ISO 100 are more natural looking. In low-light situations it’s best to just bump up the ISO to ISO 400 as the difference between 200 and 400 is very minimal.

-When using ISO 200 and 400 on the N82, a lot of noise reduction is applied. The amount of noise reduction used in ISO 200 and 400 is dramatically more than ISO 100. If you want to keep the details high using ISO 100 is recommended. When compared to digital cameras the amount of noise reduction is still excessive, but when compared to the N95 and N73 they have toned it down quite a lot. The noise reduction algorithm used seems be much smarter being able to reduce noise yet affect image quality a lot less. It also seems to increase the noise reduction as the ISO level increases instead of applying the same amount all-round. This for me is the best solution.

-In ISO 400 and 200 extra edge enhancement is applied. The amount is a lot more on ISO 400. They need to do this to make up for the blurring effect of the noise reduction. The higher amounts of edge enhancement in ISO 400 make for a bolder and crisper looking image. Fidelity to the orginal scene aside, people would actually prefer this.

Images produced by the N95 and N73 were indeed impressive, but due to the aggressive edge enhanced and noise reduction I always felt a gap between them and a stand-alone digital camera. The N82’s images look extremely clean and it’s only when you increase the ISO level and you zoom in incredibly close do you notice the noise reduction and edge enhancement being applied. The amount of enhancements used is dramatically less than the N95 and especially the N73. When we compare the N82 to stand-alone digital cameras the amount of noise reduction and edge enhancement is too much, but currently it’s the best imaging device in the mobile world. To increase the image quality it seems Nokia is going to have to use a larger sensor size, as it’s common knowledge that sensor size affects image noise and dynamic range. There’s only so much image enhancements can do. When it comes to ISO performance: if you want to keep lots of image detail it’s best to use ISO 100. If you want to brighten up the image without using flash with the added plus of the higher ISO’s ability to decrease the effects of camera shake it’s best to go all the way to ISO 400 as the difference between 200 and 400 is minimal and many people would prefer the bold look offered by ISO 400. To answer our final question: Is the noise level of ISO 400 a lot more then let’s say ISO 100? No, as the noise reduction masks the noise and the edge enhancement tries to make up for the details being lost. In the end ISO 100 should be used in conditions with enough light, use 400 when you want to counter the effects of camera shake and brighten up the scene. While we’re on the subject of camera shake I think it’s time for Nokia to use a proper Optical Image stabilization system: This will not only allow you to use a low ISO in darker conditions, but make up for a camera shake.