When 20 megapixels is really 50 megapixels. By Jim Chung.

Camera & Technology

May 22, 2022 ·

Josh Reichmann

Recently, both OM Digital Solutions (a consumer camera division spun off from Olympus’ core medical business) and Panasonic introduced exciting new micro four thirds (m43) camera bodies – the OM-1 and the GH6, respectively. This news confused many photographers who expected the m43 format to have gone extinct. The m43 sensor is significantly smaller than a full frame sized sensor (equivalent in size to a 35mm film negative) and the laws of physics dictate that smaller sensors deliver higher noise, greater depth of field and poor low light performance. It’s interesting that nobody was similarly critical when the 60% smaller APS sized sensor was introduced.

Both Olympus and Panasonic use creative solutions to address these shortcomings such as developing fast glass, class leading sensor stabilization, and computational photography. Critics point to the 20-25 MP sensors, (respectively OM and Panasonic) used in the new bodies and the 46 MP sensor in the new Nikon Z9. However image quality and resolution is not compromised because the m43 pixel density equivalence in full frame is 80-100 MP. What is true is that making very large prints of a 20 MP image is more difficult than with a 47 MP image.

Olympus was listening in 2018 and pioneered the Hi Resolution Mode, which can generate a true 50MP image from a 20 MP sensor.

Explaining the computational process can be best achieved by describing its initial implementation, which required the camera on a tripod. The camera uses the stabilization motors to precisely move the imaging sensor in either one or half pixel steps. The sensor moves counterclockwise in three one pixel steps to allow the Bayer layer to collect true color data, and then the sensor shifts a 1/2 pixel to the left and up which theoretically doubles the vertical and horizontal resolution. The sensor then repeats the Bayer layer color data movements. A total of 8 images have been taken and the data combined in camera. Images look better because color reproduction is now accurate and not estimated by interpolation algorithms, dynamic range is increased due to noise reduction (2 ISO steps) from image stacking, and the image looks sharper since false color fringing and moiré are eliminated. Resolution gains are also achieved because in a Bayer Color Matrix, only green data is used for detail rendering and is upscaled as a luminance layer over the color layer. With the data from the 8 images, every photo site is represented with green channel data.

Both the OM-1 and GH6 can generate high resolution images hand held because of advances in the processing speed of the camera chips. The sensor stabilization is turned on and off cyclically to help stabilize the sensor and also to record the hand held drift of the camera while 16 images are taken. In the GH6 the best 8 images are combined and areas showing objects in motion are isolated and unstacked to preserve their sharpness. The process can take over 10 seconds and a 100 MP image results. In the OM-1 all 16 images are stacked with any regions in motion recorded as a blur but the process is much faster. The OM-1 does only produce a 50 MP so not double the resolution but approximately 1.6x (

Being an amateur doesn’t mean we are without means to test the marketing claims of any camera company.

The modern standard for resolution testing is the ISO 12233 resolution test chart and I would recommend buying professionally printed charts which are offset printed on matt paper with 10:1 contrast. You can download the test chart in pdf form and print it on photo quality inkjet paper at your printer’s maximum resolution, but without vector graphics inkjets are unable to print curved lines cleanly.

Imatest is the industry standard software to use but a single user license costs more than the chart! I was happy to discover that Olympus released a very simple freeware more than a decade ago and it is still available on the CIPA webpage, HYRes3.1 is crude and requires some trial and error with the parameters to understand how to get it to work correctly.

HYRes3.1 runs on 32 bit architecture, working for XP (actually via Parallels on MacOS).

I tested a variety of lenses – primes and zooms, around 40mm focal length and of a range of price and quality.

Resolution gains are self evident with the 50mm f/2 lens using (Left) high res mode and (Right) normal mode. The numbers refer to line spacing equivalent to hundreds of lines per picture height.

The bar graph demonstrates very concisely an approximately 1.5x increase in resolution through the center zones of several lenses, resolution expressed +/- standard error of mean with n=3.

In closing I’d like to demonstrate it is possible to use the hand held High Resolution Mode on living subjects, and not just landscapes. It is challenging to do it with the 300mm f/4 Pro telephoto prime and took a few tries until I convinced this House Sparrow to pose without moving for several seconds.

Jim Chung

May 2022

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