A comparison of 4K to 1080p downscaling with GH4 / Ninja Star vs. FCPX

[studiodc]

So, I've just shot a quick test using my GH4 and a Ninja Star. The test is to check the differences between the internal HDMI-based 4K downscale and the 4K -> 1080p downscale using the 4:2:0 8-bit H264 as a source.

The images can be downloaded in full resolution here: https://www.dropbox.com/s/e6o06zoowk7z5fh/GH4%20Test%20Images.zip?dl=0

See the attached files for some side-by-side 100% comparisons.

Images are from the GH4 (set to a gently tweaked CineV, 4K 100M 24p - really 23.98, 180 degree shutter, Sigma 18-35 at f/2.8 on a Speedbooster at ISO 400, auto white balance, tungsten lighting).

They were captured to 1080p using the following workflows:

Clip 1: Recorded in GH4 (4:2:0 8-bit H.264 4K) then downscaled in Red Giant Bulletproof to 1080p ProRes 422HQ.

Clip 2: Recorded in GH4 (4:2:0 8-bit H.264 4K) then downscaled in FCPX by adding to a 1080p timeline.

Clip 3: GH4 HDMI out (4:2:2 8-bit) to Atomos Ninja Star (ProRes 422HQ)

Clip 4: GH4 HDMI out (4:2:2 10-bit) to Atomos Ninja Star (ProRes 422HQ)

All clips were then placed in an FCPX timeline (Clip 2 was placed as a 4K file), then a frame was exported as a TIFF uncompressed file at full 1080p resolution. No effects, grading, or anything else was applied.

I tried to choose a subject (ColorChecker Passport and tomato, lit just off-axis with a side light accent) that would both provide some sharp edges as well as gentle gradients, and the green/red of the tomato should hopefully accentuate any actual chroma sub-sampling issues that exist. Camera was on a beanbag so please excuse any pixel-level misregistration, I don't have my tripod handy right now.

I hope this helps someone.

GH4 Test Image 1.tiff

GH4 Test Image 2.tiff

GH4 Test Image 3.tiff

[MattH]

I couldn't see much of a difference personally.  Obviously the 10 bit would probably become apparent after grading.  As far as the downscale, perhaps something with very fine detail and diagonal lines would bring out the differences.

[MattH]

On second look, on the first image the Ninga star examples seem to ad a red fringing to the left edge of the orange sqares.  In the second image the ninja star  examples have darker shadows on the leaves. It could be this that gives the impression of more detail.  This is also aparent in image 3 where the ninja star examples seem sharper, but it is perhapse a more artificial sharpness.