New Rumor: No 4K crop on Canon's next APS-C DSLR's
A new rumor from Canon Rumors is suggesting that the 90D that is expected to come out in August of this year, will have 4K video without any meaningful crop. That seems to suggest that there will be a slight crop factor unless they are talking about the difference in aspect ratios between video and stills.
To do full sensor width 4K on an APS-C sized sensor isn't especially that difficult for Canon especially if they resort to doing line skipping or binning to accomplish it. Especially considering they already and still do line-skipping for full-width 1080p. It's true that it would have to be a "new sensor" and not just a reuse of an existing sensor, but it's not technically challenging.
What would be more impressive is if they went up to oversampling which other 4K cameras now do, of which, there is no indication that Canon has progressed that far with technology. The difference between line skipping and oversampling is that with line skipping, the camera does just that, skips rows or columns as it reads the sensor to achieve a faster read on the sensor, and also to minimize data. Instead of reading 4,000 lines on a 24MP sensor (or 4600 on a 32.5MP sensor) it will read approximately 2160 rows instead. Downsides to lineskipping are that aliasing is more pronounced, and visually, the video isn't as sharp as oversampled video.
Oversampling requires much more data to be read and processed from the sensor. Oversampled video puts a greater strain on the processing because each frame has to be converted from RAW and then downsized to the appropriate 4K or 1080p resolution, and then video compressed. The downsizing is an additional step that a line skipping 4K solution doesn't have to contend with. This is more of a technical challenge. Assuming the new sensor could handle the image sensor being read fast enough for full width and oversampled video, the processor itself would need an efficient CPU to shoulder the greater amount of work. This may have to wait until DIGIC 9 makes an appearance, likely sometime next year.
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