M50: No DPAF in UHD: Marketing decision or technical limit?

Started Jul 22, 2018 | Questions thread
nnowak Veteran Member • Posts: 6,477
Some analysis...
4

The M50 can shoot 1080p60 with full DPAF. When cropped for the 16:9 aspect ratio, that region contains 20.3MP. The M50 is reading out more than 2MP (1920X1080) from that area and then downsampling to 1080p. Canon may still be employing some line skipping and pixel binning, but based on the progressive quality improvement from the original M to M3 to M5, and now M50, the total readout is at least 4MP (likely more).

If you add in digital image stabilization, the M50 is still reading out the full sensor width, but the camera is doing dynamic interpolation of every frame. Data from the lens IS system, internal camera gyro, and the image sensor are all processed in real time as the camera resamples each frame.

With the right lenses, the maximum AF area during 1080p video is 17.8MP. With other lenses, the AF area covers 16.2MP of DPAF points.

When shooting 1080p60, the M50 is reading out at least 4MP of data at 60fps while simultaneously performing AF calculations with data from 17.8MP of DPAF points. Digital IS can also be performed at the same time which adds an extra interpolation load to the DIGIC. The M50 does all of this with no heat issues.

Switching to 4k, the M50 is reading out 8MP of data at only 24fps. Even though the AF area only comprises 8MP of DPAF points, DPAF is disabled. Digital IS is still possible and the M50 is still reading out 8MP of data, but the image is cropped, interpolated, and upsampled.

All h.264 encoding in the M50 is handled by dedicated hardware that is independent of the processing used for the AF system. The h.264 encoding is typically the most computationally intensive part of video recording and I believe it is the primary source of heat in Sony cameras. The M50 can encode 4k and write to the SD card without any heat issues.

So where is the 4k bottleneck? The backend processes of h.264 encoding and writing to SD card are all working without issues. At the frontend, the M50 is capable of reading out at least 4MP of data at 60fps while simultaneously performing full DPAF and digital IS. The data volume from 4MP at 60fps is equal to the volume from 8MP at 30fps.

One more data point... the 5DIV can shoot 4k30 with full DPAF using a cropped region of the sensor. The 5DIV is using a much older DIGIC 6+ and digital IS is not possible with 4k. The problem with the 5DIV is the backend as the 5DIV lacks an efficient h.264 encoder. To avoid heat issues, the 5DIV foregoes any h.264 encoding and saves 4k footage as a stream of JPEGs.

Not only should the hardware in the M50 be capable of running DPAF with 4k, but it should be able to do 4k without a crop. Some line skipping and pixel binning may be needed, and maybe digital IS would be disabled, but uncropped 4k30 with DPAF should be possible without any issues.

The video limitations of the M50 really look like a marketing decision and not at all related to any hardware deficiencies.  The real unknown is what price point Canon deems acceptable for uncropped 4k30 with DPAF.  Will the M5 II be that point, or will it only get cropped 4k with DPAF?  Will Canon withhold uncropped 4k for the upcomming mirrorless full frame camera?

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