EX1 8bit vrs 10bit uncompressed test.

[Jim Arthurs]

I've been have great success with my EX1 doing blue and green screen work, both using the native codec on location, and going live into my NLE through HD-SDI 8bit uncompressed when working in the studio.

Even so, I have been wondering lately what I might be missing by not taking full advantage of the EX1's 10bit HD-SDI output. Specifically, would there be noticeable and practical improvements in the quality of the image if I worked in 10bit vrs 8bit for capture? We know as certain fact that the EX1 is 10bit, and those are active useful bits, not just a cheap padding up from 8bit.

So, I set up a test. I photographed a white card lit for a very shallow gradient of light across the surface, and defocused the camera to help smooth the image. My hope was to force an image that would display banding (you know, like you see in a pale sky), and a very narrow gradient of 45 to 55 IRE should be subtle enough to do it.

I recorded this into my NLE as both 10bit uncompressed and 8bit uncompressed clips. I then used Digital Fusion to save out png's of the resulting clips, being VERY CAREFUL to maintain the clips native colorspace throughout the export. The 10bit PNG is padded up to 16bits on save, and the DF flow was in full 16bit float colorspace. The 8bit PNG was saved out from an 8bit color space project.

In Photoshop I ramped the levels of each file until that 10 IRE gradient range was blown out to white on one side and black on the other (staying 16bit in Photoshop). The same was done in 8bit space on the 8bit file. I then dropped the 10bit file down to 8bit and split screened it with the 8bit version.

http://ftp.datausa.com/imageshoppe/o...10bit_Test.png

Interestingly, The 10bit isn't particularly more subtle than the 8bit one. As a note, the area in the frame blown to white is just imperfection in the lighting. When expanding a 10 IRE recorded gradient out to black and white you're going to see everything.

At this point I'm not seeing a practical advantage in working with 10bit and the EX1, at least at the image recording stage. This test shows extremes beyond the demands of any color correction and needs for good key work.

Having said that, I want to make the files available to any who wish to manipulate them in any way they wish.

http://ftp.datausa.com/imageshoppe/o...compressed.zip (20megs)

I've zipped up the source files (and another more visually interesting example of colored pencils). Feel free to download and do your own image comparison tests/experiments in Photoshop. Remember to keep each image in its native color space until you're done with your image manipulation.

I'd love some thoughs on this, and if anyone has access to the necessary equipment and workflows to duplicate this experiment I encourage them to do so. My results are based on the EX1, Leitch Velocity HD NLE and using Digital Fusion for processing. Your mileage may vary, etc.

I'd love to see a situation or example where recording 10bit from the EX1/EX3 results in any advantage whatsoever. As far as I can tell with these tests, there's no reason to do so. I think it's also important to stress that we're talking about practical results and not theoretical advantages. Looking forward to the feedback,

Regards,

Jim Arthurs

[Abdulla Nadym]

Visually there seems to be not much of a difference from the images youve posted. I guess that will apply to color correction, keying & effects on the video.

In conclusion you are suggesting that based on your experiments there is NO considerable advantage of using 10bit SDI uncompressed video from the EX1 over the default 8bit MPEG videos from te solid state media?

suppose one has 10bit video, but to my knowlede it cannot be cut & or color corrected using Vegas? what editing software can take advantage of this? Digital Fusion as youve mentioned is a compositing application & editing though it may not be an ideal workflow of everyday editors.

As for the 8bit work im doing, if shot with good lighting, focus etc, the it holds up well throuhg Vegas CC & finally broadcast.

As im just a beginner suggestion are most welcome

[Paul Curtis]

Jim,

I would think the biggest advantage of using HDSDI out is 4:2:2 and better compression possibilities.

But then shooting greyscale has equal amounts of RG and B which is a safer test. If you did the same with one channel (the blue sky) i would think that 10bit would be more helpful. When you're skirting around the edge of range and then working with the images - posterisation in highlights, or lifting the shadows and pushing around the channels rather than simply comparing a graduation, that's when it could make a real difference. If you don't do this or need to then 8bit will be plenty.

I know i can band 8bit when grading but you can cover up a lot of it with subtle diffusion however there are times when a little bit of extra information would have been useful.

But then i would take 4:2:2 and better compression (leaves in the wind for example will make life difficult for the compression) as the reasons to go to external HDSDI recording.

cheers
paul

[Jim Arthurs]

Thanks all... if I have the time, I'll run the test again, but this time stepping all the way from 0 IRE up to 109 IRE in 10 IRE increments with the gradient test and the EX1. While I'm doing it, I'll compare not only 8bit vrs 10bit uncompressed, but the same with mild compression simulating 100Mb/sec recording, since the NLE I'm using will let me do that.

We've all seen blue skys band like Paul mentions... I'm curious to simulate exactly the conditions we would see that under, and if the potential value of 10bit is crippled by compression...

Regards,

Jim Arthurs

[Steven Thomas]

Thanks Jim. If you can find the time, this would be a great test. This would help find the limitations under certain conditions for 8bit.