SJ5000+ Still Image Quality

On paper the new SJ5000 models promise a big jump in quality over the previous SJCAM model, the SJ4000, which boasted of 12 MP still images but in reality only produce massively upsized files from its native 2MP imaging sensor. By contrast the two base models SJ5000 and SJ5000wifi have new 14MP Panasonic sensors and the SJ5000+ bumps up to 16MP. The number of pixels doesn't tell the whole story though and a I'll start with aquick resume of the type of requirements which govern Action Cam optical design. Small overall size and light weight is one of the factors. The GoPro aesthetic is of wide angle view with fish eye distortion. This type of lens has a deep field of focus so it is possible to have a fixed lens, (no autofocus) and have everything sharp from a couple of feet away to infinity. Fisheye lenses for large sensor cameras such as DSLRs are heavy and expensive. GoPro style cameras use a small and cheap vesion with correspondingly small sized imaging sensor, in the case of the SJ5000+ a 1/2.33" Panasonic MN34120PA CMOS type. It's dimensions are a tiny 5.8x4.3mm, close to those of the sensor of an iphone 5 and considerably smaller than that of a DSLR which has sensor dimensions 36x24mm.

With that in mind any assessment of image quality needs to be realistic and take the physical limitations of the camera into consideration. Small sensors invariably exhibit more noise especially in High ISO low light situations and dynamic range is limited.

I have seen some impressive images shot with mobile phones and the potential for decent stills quality (if only under ideal conditions), piqued my interest in buying and trying an SJ|5000+.

First off, the fisheye look is not one for all subjects the ultra wide angle makes even middle distance subjects appear to be a long way away and don't even think of photographing your nearest and dearest close up unless they can tolerate being portrayed with a huge nose.

The following images of Exeter Customs House on the Quay show what can be achieved with a little massaging in Photoshop. Remember all these images are my copyright and may not be copied and published elsewhere. If you wish to refer to them please link to this blog.


First the original image sized down to 1200 pixels wide:

The first impression is that it is drastically oversharpened making it look very gritty and accentuating noise.

This is demonstrated with the two examples below both 100% crops. The "Befores" are as shot, the "Afters have had a slight blur and some smart sharpening and noise reduction in Photoshop,

Before

 

After

 

 



 Before

After

 

Despite this there are still visible sharpening haloes and artefacts. A shame as it would have been possible to include a choice of sharpening strengths in the image menu so that it could be applied at the proper stage in post processing.

 

 



I was pleasantly surprised by the performance of the lens which is essentially a $2.99 item sold on Alibaba. Detail is held to the edge of the frame and the aggressive sharpening that the camera applies really isn't necessary. What isn't a surprise is the high level of chromatic aberration exhibited. This is of the blue-yellow variety and can be seen in the 100% crop sample from the right hand edge.

 



Before

 

The "After" crop below has had B-Y chromatic aberration correction carried out in Photoshop at a level of +66.6 which reduces it somewhat, however there is purple fringing visible at high contrast boundaries which is more stubborn to fix.

 

After

The final image is a 1200 pixel version of the final image  which has additionally been brightened using curves, straightened cropped and had  bit of de-fishing applied.

The conclusion is that with some light post-processing quite usable still images can be produced provided care is taken not to overexpose. Unfortunately for use in professional publication the aggressive sharpening applied in camera limits the size at which they can be reproduced, however quality is adequate for display at full size on a 4K ultra high definition TV screen.

There has been some debate over the accuracy of the SJCAM SJ5000+ AWB (automatic white balance). This interior shot was taken in a glass roofed conservatory lit indirectly room on the north side. Sunny day blue sky and clouds outside. I can only say that colours look absolutely spot on to me. Exposure set to -0.3EV and image brightened slightly in post processing.