Data Rate Upper Limits Warning: Long Post Ahead
Like I said in the previous post, I would like to create a test which can be easily and quickly replicated by anyone, in order to have a coherent comparison between the performances of various cards at different resolutions.
Because filming the LCD Screen leads to moiré artifacts which biases the results, I went outside to film various scenes at 2.5K to get a baseline. I will then create a pattern which can be printed on plain paper and filmed with the camera, with enough details to generate files of comparable size to real life recordings.
This test will also check where the "Data Rate Overload" occurs in real life (See my previous post)
The motivation for going through this is as follows:
1- I just purchased a high-capacity 200MB/s card to test the upper limits, which cost me half the price of the Camera.
2- The Students I help would rather spend that money on beer...
3- It took me 4 months of reading and testing before being able to use that EOS M to its full potential. This negates any low-cost benefit afforded by the cam. But if there was a set of guidelines written in a few posts, newcomers would be able to use the cam to its full potential in a fraction of the time (And with cheaper cards, if necessary).
4-It's always nice to have a list of several alternative cards. For example, the latest Sandisk Extreme Pro did not work well until the latest Overclock module.
Short Answer: 1- A test pattern which can generate 70-80MB/s files at the target exposure and 90MB/s+ at ettr would simulate real-life conditions.
2- The Bench.mo would be a lot closer to real-life use if it also ran a sustained-write test (1-2 min?)
3- With 240MHz Overclock, there is no need to heavily underexpose the image to get decent recording times at 12bits, and 14bits with little restrictions (2.5K tested here, but theoretically applies to 5k frtp and 1080p).
I avoid recording at 10 bits, as it gives a reddish tint to the noise in the image, and more noise overall. So 10bits should be carefully exposed to minimize the noise, and 12/14 bits should be preferred if there are lots of dark regions in the image.
Look at scene 5 below to see a real-life example of exposure triggering a frame corruption message.
Details:Exposure being a key factor in achieving near-continuous recordings (Or long enough clips), let's establish what I consider a bright-enough, well exposed image. In the examples, I also included graded versions, so that it shows that the tests are not unreasonably brightly exposed.
I had the scopes in my MLV App modified to make it easier to evaluate the image. I left those in every screenshot, so that it shows that no clipping is taking place. (Click or download images to enlarge)
ScopesLabel.cpp
A few examples where I exposed with histogram at 1.0 and the main subjects Grey and Green with hints of yellow, when using the False Colors:
Example 1 Before and After Grading:
Example 2 Before and After Grading:
Example 3 Before and After Grading:
These 3 examples yield between 62 and 64MB/s @2.5K 14bits, and the other clips I have top at 79MB/s which means that it is possible to get a guaranteed 30 seconds per clip (Max 1:45min with lvface, or 3:00+ with lvface+aewb hack) with a Sandisk Extreme 256, without having to heavily underexpose the image. With these parameters, the images are quite clean, with some light noise in the shadows, like any other camera, even the expensive ones... (See the previous video I posted:
https://bit.ly/3eKo5e9)
Exposing a little hotter brings the noise lower, at the expense of shorter recording times. Which leads to the next test.
Examples recorded with Histogram showing 0.2You can look at the Data Rates Here. Each group of 10-12-14 or 10-12-14-14 bits are the exact same image, recorded at different bit Depths. The extra 14 bit recording is to check consistency or a lower exposure.
Scene 1, very bright Highlights, 80.39 MB/s @2.5k 14bits
Scene 1 Graded
Scene 2, Well balanced scene with some bright elements (The shiny objects are usually what chokes the recording). 74.27 MB/s @2.5k 14bits
Scene 2 Graded
Scene 3, Well Balanced scene with less shiny spots (Allows a brighter overall image) 76.5 MB/s
@2.5k 14bits
Scene 3 with histogram at 1.0, lowers the data rate by 6.5 MB/s, and you get richer colors too
Scene 3 Graded
Scene 4, Closeup with a lot of details and a very shiny object. This combination made the recording stop early at 14bits, with
91.23 MB/s
Scene 4 Graded
Scene 5, Triggers frame corruption.This scene, with a lot of details and reflective mosaic triggered a frame corruption error at 14 bits.
Graded
Recorded with exposure right before it triggered a frame corruption,
91.59 MB/s at 2.5k, 14bits
Lowering Histogram to 1.0 and 2.0 yields a data rate of 88.1 and 76.16 MB/s respectively
When the image is that bright, bumping up the ISO has a negligible effect on data rates:
Also note that moving the camera makes motion blur, and a blurry image decreases the data rate.
I won't post those clips, as this post is long enough already!
I did not let the camera record long in this test, to speed things up. For actual recording times, Have a look at the SD card tests I posted, which were in line with the Data Rates obtained here.
Maybe everyone could chime in as to what constitutes "a long enough clip recording time" to get the job done at higher resolutions.
Build Used: crop_rec_4k_mlv_snd_raw_only_2022Sep15.EOSM202
Cards: Sandisk Extreme Pro 128GB 170MB/s, Sandisk Extreme 256GB
Lens Ef-M 32mm F1.4
