Noise, resolution and sensitivity

These images show 72ppi (100% on a computer screen) sections of images of a resolution chart, captured using the Sigma 105mm f/2.8 macro lens. We show the section of the resolution chart where the camera starts to fail to reproduce the lines separately. The higher the number visible in these images, the better the camera’s detail resolution is at the specified sensitivity setting.

This is the third time we have seen a 16.1-million-pixel sensor in an Olympus camera, with both the Olympus OM-D E-M5 and Pen E-PM2 including the same unit. In both cases we have been impressed with the image quality produced. Although other cameras may use higher-resolution sensors, 16.1 million pixels is a good compromise that allows the E-PL5 to produce detailed images while keeping noise to a minimum. This means it is possible to make decent-sized prints from the digital images.

Generally, the E-PL5 does an excellent job of reducing chroma noise in the JPEGs it creates in-camera. Speckled colour is largely non-existent, even when shooting at high sensitivities. Luminance noise is far more difficult to reduce, however, but the E-PL5 controls it quite well in-camera up to around ISO 800. At ISO 1600, there are hints of speckled noise and this increases with the sensitivity. The camera tries to correct this by smoothing out some of the noise, but this also reduces detail. Having said that, at the sensitivity settings most photographers will use – ISO 200-1600 – noise shouldn’t be too problematic.

One thing the E-PL5 is guilty of is overprocessing JPEGs. In some images taken at ISO 200, edges are slightly oversharpened, which is noticeable due to a hint of luminance noise. Slight image artefacts appear occasionally in shadow areas, although these aren’t noticeable in raw images. I would suggest reducing the in-camera sharpening of whichever image style you are working in, and also using the Super Fine JPEG settings. Strangely, this is tucked away in the custom menu, rather than in the JPEG/raw menu. It is odd that Olympus has always left this setting in the custom menu in its E-series DSLRs and micro four thirds cameras. Why not make it far more obvious? After all, it improves the quality of JPEG images by compressing the image less.

Opening raw files in Olympus Viewer 2 makes it clear that some processing of raw files is going on in the background. Even with the noise reduction set to Off, it still seems that some basic luminance noise reduction is applied. The latest updates to Adobe Camera Raw 7.3 and Lightroom 4.3 include support for the E-PL5 and give a clearer idea of what the raw files look like, and they are very good.

Luminance noise is obvious, but colour noise is well controlled and is easy to remove almost completely. I tend not to apply too much luminance noise reduction as it reduces detail. I found that just nudging the luminance noise reduction slider to about 5, and then applying a slight sharpening and a touch of local contrast with the Clarity tool, created just the right compromise between luminance noise and detail, particularly in ISO 800 images.

At lower sensitivities, just a slight sharpening and tweak to the contrast was about all that was needed.

In terms of resolution, the 16.1-million-pixel sensor is about on a par with other 16-million-pixel cameras we have tested, reaching around 28 on our resolution test chart.

Image: Taken at ISO 400, this black & white shot shows very little luminance noise in the shadow area

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