How to test the actual visible differences in compression ratios

[TJ Hellmuth]

I'm working with a photographer on some television commercials, mostly for fashion and beauty brands. Coming from the photography world, he's not used to thinking of his raw files having compression, and to him, he'd theoretically like to shoot 1:1 ratio because he simply wants the best possible quality. So he'd like to do some tests to actually examine the differences between compression ratios. It would also be great to know exactly we are compromising when shooting at higher frame rates and HDR. i've read lots of rules of thumb, but also seen very conflicting practices in this regard. Some DP's will not budge from 5:1 whatsoever. other people on the forums say that 8:1 is a good sweet spot for non-effects work. so I'd love to see the difference for myself.

Is there an example online of anyone looking at just how far they can push these files and what exactly you loose visibly when you shoot at higher compression rates? I'd like to form a test for him, and I'd love to post the results here but I'm trying to figure out how to test. What will the weak points be that I should focus on? color depth? subtleties of skin tone? range? Sharpness? Any links or ideas for a good test would be appreciated.


Thanks!

TJ

[Timur Civan]

Depending on how r3d compresses a frame, if you create a small 3" section of ultra fine detail, like a piece of a mft chart, then for the rest of the frame have a ton of fine detail moving, like filling the frame with moving water, and shoot the various compressions. You should see the compression in the chip chart.


Again this depends on if r3d compresses each frame independently, regardless of content. Also, a range of contrast would probably be good.

I see a lot of artifacting in 12:1, but almost none in 10:1, so it seems there is a sweet spot where the bandwidth can overcome the details.

[TJ Hellmuth]

Thanks for the reply. This sounds like a good plan. Perhaps a shiny colorful pinwheel might be a good alternate to the water in terms of rigging and range of color and latitude. This sounds like a good test. Thanks!

[William Robinette]

I see a lot of artifacting in 12:1, but almost none in 10:1, so it seems there is a sweet spot where the bandwidth can overcome the details.

When shooting for a 1080p post and a finish possibly smaller then that (720p/SD) are you content with shooting 10:1 to save space? I'm talking straight cut and output; no compositing, green screen, crazy color grading.

[D Fuller]

Thanks for the reply. This sounds like a good plan. Perhaps a shiny colorful pinwheel might be a good alternate to the water in terms of rigging and range of color and latitude. This sounds like a good test. Thanks!

The secret to stressing the codec is detail. The pinwheel is likely to create motion blur, which actually makes it easier for the codec, because it has less detail (more blur). Deep focus shots of water, as Timur suggests, or gently moving leaves are ideal stressors. Lots of fine, sharp detail=significant challenge for a codec.

[Rob Ruffo]

Also, try to pull an aggressive HSL qualified secondary grade - any compression noise will pop right to attention.

[Les Dittert]

The compression Red is using in R3D's does not get effected by moving objects, it does not use motion vectors like mpeg or h264.
So a tree moving in the wind is no harder for it than a static tree.
Lots of random detail is stressful. Gamma up the image and look at things like tree bark.

[Erwin van Dijck]

I did a little test some time ago and found that at 8:1 the visible noise is looking much more pleasing compared to 12:1.

[Timur Civan]

When shooting for a 1080p post and a finish possibly smaller then that (720p/SD) are you content with shooting 10:1 to save space? I'm talking straight cut and output; no compositing, green screen, crazy color grading.

I do 10:1 for doc that isnt going through a DI and is just being bumped down to Prores for a quick edit up to You tube.

anyhting that has a chance of being graded is shot 5:1, 3:1 for VFX shots.

[Shane Kelly]

I shoot 10:1 for documentary type shoots, 5:1 for greenscreen. 8:1 for most other jobs.
1:1 sounds excessive.