Inogeni 4k hdmi to USB3 question regarding video quality

[fordry]

So I am looking at this as a potential poor man's shortcut/alternative to better footage than the internal recording on a GH4. I understand the drawbacks in terms of portability and such and would prefer this thread not turn into a discussion of the ease of how they are used and the extra features or drawbacks each of the solutions have because I know all that stuff. My question is about the quality of the video being captured. The Inogeni states that it captures at 12-bit 4:2:0 in 4k mode. I have seen several reviews of 4:2:2 and 4:2:0 and 8-bit vs 10-bit but my issue with them is that it seems they throw bit-depth and chroma subsampling around interchangeably remarking that stuff I thought was related to the bit-depth(banding) is affected by the chroma subsampling for instance. I get that they may be related but its something I don't understand very well. So, compared to what you get with a Shogun or compared to the workflow of downsizing the internal recording to 1080 to achieve an alleged 10-bit 4:4:4 signal, what are you getting with 4k at 12-bit 4:2:0 out of the Inogeni? Or what are you not getting by only having 4:2:0 chroma subsampling particularly if you planned to downsize it to 1080 to get the 4:4:4? And yes I know the GH4 only puts out 10-bit...

 

[Floris Liesker]

I am looking for the same thing: a poor man's solution for recording 4K to my laptop. In my case from the A7S. I own a GH4 as well but I'm fine with its internal recording quality. The A7S only records 1080P internally and it does a terrible job at downsizing the 4K image, creating colorful artifacts at every high contrast edge. I'm looking into the Inogeni 4K hdmi to USB 3.0 as well, I'm not sure if the device will do the job properly but I can shed some light into the bit depth/chroma subsampling issue. In theory those two things are unrelated. Bit depth is the precision of the color (8 bit is 256 steps per channel and 12 bit is 4096 steps per channel, so it's better). A low bit depth causes banding. Chroma subsampling in essence is a lower resolution for the chroma (compared to the luma). So it's a spatial thing. Chroma subsampling will not introduce banding, it will smear out colours over adjacent pixels. The numbers 4:2:2 or 4:2:0 etc dictate how the resolution of the color channels is distributed horizontally and vertically. In the case of 4K 4:2:0 this will result in a 4K image for the luma and 2K for the color channels. Before chroma subsampling is done the image needs to be chroma filtered to avoid aliasing but it's unclear to me if and how the Inogeni does that. The GH4 does output 10 bit so there is some advantage to be expected using the Inogeni however if its chroma filtering is absent or not on par with the GH4's internal codec the image will probably look worse. I don't want to record on a desktop computer with PCIe ports but if you do you could consider the new Blackmagic Intensity Pro 4K card. It's even cheaper than the Inogeni, it does 4:2:2 at 10 bit and it only costs $199.