The actual sensitivity of each indicated ISO is measured using the same shots as are used to measure ISO noise levels, we simply compare the exposure for each shot to the metered light level (using a calibrated Sekonic L-358), middle gray matched. We estimate the accuracy of these results to be +/- 1/6 EV (the margin of error given in the ISO specifications). We found that measured ISO from the Samsung NX200 is accurate across the ISO range.
Noise and Noise Reduction (JPEG)
The NX200 only offers two noise reduction setting - On and Off. When switched on noise reduction only kicks in at ISO 6400, so the setting really only has an impact at the two highest sensitivity settings. When shooting JPEGs the camera of course always applies 'some' noise reduction, even at the 'Off' setting.
The noise graph, shown here, doesn't tell the whole story and it is clear that noise reduction is keeping measured noise levels low. Looking at the graph in our noise widget the NX200's measured noise levels are comparatively low throughout the ISO range but some of that, especially at higher sensitivities, is achieved through application of strong noise reduction which leads to an increased loss of fine detail.
At 100% on screen, very little noise is visible at low sensitivities but loss of fine detail through noise reduction becomes obvious from ISO 800 upwards. That said, at this setting it's only apparent when images are viewed like this, critically, at 100% on screen. There is a fairly huge leap between ISO 1600 and 3200 at which point chroma noise makes a prominent appearance and the smearing of detail becomes more intrusive. At the two highest ISO settings - ISO 6400 and 12800 - the smearing of detail is fairly extreme at both NR settings but the 'NR On' output is cleaner which arguably makes it the better choice. It significantly reduces the ugly chroma noise 'blotching' which is otherwise visible even in downsampled images. The medium- and low- contrast detail in our test scene is all but wiped out by then but it's worth noting that high-contrast scene elements are still relatively well-preserved, which makes these images usable at least for small prints and web use.
RAW noise (ACR 6.6, noise reduction set to zero)
The amount of NR applied 'under the hood' is not high, but it does vary by camera (Adobe is attempting to normalize output across different sensors), so we are still looking at a balance of noise and noise reduction, rather than pure noise levels. However, the use of the most popular third-party raw converter is intended to give a photographically relevant result, rather than simply comparing sensor performance in an abstract manner.
Converting the NX200 output in Adobe Camera RAW 6.6 suggests that the camera's noise performance at a sensor level is better than what the JPEG results would make you think. Despite the NX200's higher pixel count the raw noise is at similar or lower levels than the competition across the ISO range. If you shoot a lot in low light and higher sensitivities and don't want to compromise on image quality, shooting RAW and applying your own noise reduction recipe can definitely yield you better results than relying on the NX200's JPEG engine. With some careful post-processing you'll even be able to 'rescue' images taken at ISO 6400 and above.
That said, as always, you should keep in mind that our assessment is based on a pixel-level view. The NX200 files contain more pixels than the competing models judgement which means that at equal viewing size the NX200 has, in terms of noise, an additional advantage over the lower pixel count competition.
During our testing we also found that, with the noise reduction feature switched on, the NX200 applies some noise reduction to raw files. Like the JPG noise reduction this only kicks in at ISO 6400 and 12800. We've included both variants in the sample widget above and as you can see the difference is quite noticeable, with visible blurring of noise and detail in the NR On files.