Sony a77 1080p video appears similar or identical to 720p capture digitally upsampled

I use an array of cameras for video work, primarly Panasonic GH2s, but also an Olympus EPL1, a 5D Mark II, a Sony a77, and the occasional Vixia camcorder. For some reason, the videos from the a77 were never usable cropped, while those from the GH2 were always okay. I decided to do a little experiment.

High level summary: The results were consistent with the a77 shooting video at 720p, likely further cropping by 1.2x, and then upsampling to 1080p.

Experiment

I mounted a Zeiss 85mm f/1.4 lens on the camera. I set it on a tripod, and focused it manually (with focus zoom) on a cardboard box. I took a photo at 1/200s, f/2.8, ISO200 (RAW, JPEG). I took a video at 1080/24p (original video). I extracted the middle frame from the video with mplayer. I took both images, and cropped out a label from the middle of the box. At that point:

Results

Actual a77 video (100% crop) What it should look like Simulated 720p on sensor Simulated 720p on video portion of sensor

The images resampled in gimp darken slightly, since gimp does not manage gamma when up/downsampling with sinc interpolation. Just to see the level of detail hitting the sensor, a 100% crop from the original JPEG:

Other points of note:


Copyright © 2013. Piotr Mitros. All Rights Reserved. Written Feb 25, 2013. Last modified Feb 28, 2013.