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Messages - tesla500

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1
Chronos User Discussion / Re: 12 -> 8 bit conversion?
« on: March 24, 2021, 05:05:27 PM »
I just got the HD 2.1 camera few months ago and it seems like a very nice camera for the money!

A small question. When saving videos in H.264 format the output is 8-bits. According to the manual sensor is 12 bits. How is the conversion done? The whole 10^12 range is resampled for the 8-bit. I have been using a camera from another manufacturer where you can select lower, middle or upper range. Having a histogram with min-max limits would be really nice for adjusting the contrast. Or is everybody just using DNGs.

The conversion from raw sensor data to a finished RGB image is quite complex. The most relevant portion here is the color space conversion, specifically linear to sRGB conversion

The data that comes off the image sensor is 12-bit, but it's a linear representation, where the pixel value is directly proportionally to the amount of light hitting that pixel. Normal images on your PC (such as your H264 video, or a jpeg image) use a non-linear color space, sRGB is a typical one. This non-linear conversion stretches the dynamic range of the image sensor out near the black side of the image's dynamic range, and compresses it near highlight side, to better emulate how the human visual system has better sensitivity to changes in brightness at lower levels of intensity.

You can see more here:
https://en.wikipedia.org/wiki/SRGB#The_sRGB_transfer_function_(%22gamma%22)

Ultimately, what comes out of this is a lookup table that converts the 12-bit (0-4095) output from the image sensor to 8-bit (0-255) sRGB. The full table is attached, but the start and end are shown below. Note how that near the low end, the 8-bit sRGB output increases nearly as fast as the 12-bit linear input increases. Therefor, the full ADC range of the image sensor is utilized, albeit only near black. This is the most important part, near highlights, the effective "gain" of the linear to sRGB transfer function is low, so the loss of a lot of ADC range doesn't effect the image quality that much.


Input linear 0-4095   Output srgb 0-255
0   0
1   0
2   1
3   2
4   3
5   4
6   4
7   5
8   6
9   7
10   8
11   8
12   9
13   10
14   11
15   11
16   12
...
...
...
4039   253
4040   253
4041   253
4042   254
4043   254
4044   254
4045   254
4046   254
4047   254
4048   254
4049   254
4050   254
4051   254
4052   254
4053   254
4054   254
4055   254
4056   254
4057   254
4058   254
4059   254
4060   254
4061   254
4062   254
4063   254
4064   254
4065   254
4066   254
4067   254
4068   254
4069   254
4070   254
4071   254
4072   254
4073   254
4074   254
4075   254
4076   254
4077   254
4078   255
4079   255
4080   255
4081   255
4082   255
4083   255
4084   255
4085   255
4086   255
4087   255
4088   255
4089   255
4090   255
4091   255
4092   255
4093   255
4094   255
4095   255

2
Chronos User Discussion / Re: How to synchronise two 2.1 Chronos?
« on: January 06, 2021, 04:00:13 PM »
Hey there! Here's a guide on how to synchronize two cameras, let me know if this procedure helps.

3
Software Dev / Re: Using two cameras with new network interface
« on: October 05, 2020, 08:08:24 PM »
Do you have both cameras connected via Etherent or USB? Is it consistent which camera fails to connect?

You can see the IP on the network settings screen, you might try pinging them both to check connectivity. You can also set a static IP address on that screen.

It is possible that the operating system on one of the cameras is corrupted in such a way that the webserver that serves the control web page doesn't work. If it's always one camera that fails, you may try reflashing the OS SD card and see if that helps.

4
Chronos User Discussion / Re: rec time stop
« on: October 05, 2020, 08:03:20 PM »
Hi Sergey,

That exact mode isn't supported, but there is something similar that may do what you want. I'm going to assume that what you want to do is have the camera record for a predefined amount of time after a trigger event, then stop.

If this is the case, what you can do is set the trigger delay to 100% in the Record Settings -> Trigger Delay screen. Once this is set, start the camera recording. Now, when a trigger occurs (external trigger input only), the camera will stop after recording one full loop in the ring buffer. Behaviourally, this is the same thing as having the ring buffer disabled.

Let me know if this helps, or if you intended something else than what I assumed.

David

5
Chronos User Discussion / Re: One line of lighter pixels in saved video.
« on: September 29, 2020, 03:49:05 PM »
Waaaaaaait. So using the exposure slider requires a black calibration afterwards?  :o Was this documented somewhere and I just completely missed it or forgot it?

Yes, that's correct, it is listed in the manual but it's easy to miss. On page 9:

Quote from: Chronos_1.4_User_Manual
Black calibration is unique for each resolution, gain setting, and shutter speed. ie. a black calibration done at 1280x1024 with 0dB gain does not apply to 1280x1024 with 6dB gain.

For best image quality, perform a black calibration after changing the resolution, frame rate or shutter speed.

This hopefully won't be required once horizontal black bar calibration is available, this is currently being worked on. Once implemented, every line will effectively have their own black cal performed every frame based on masked-off black pixels on the sides of the image sensor.

6
Chronos User Discussion / Re: New 3350 mAh battery
« on: June 16, 2020, 12:34:23 AM »
I'm curious to see too! I don't know of any of these batteries, other than the (obscenely expensive) OEM Nikon one, that actually meet their capacity spec.

When selecting a battery to ship with the camera, I ordered many different versions and tested their capacity. None of them met their stated capacity, for example, the included DSTE battery that comes with the camera claims to be 3Ah or something like that, and I measured it at 2.2Ah. Far from spec, but not far behind the Nikon one, and about 1/5th the price. The DSTE battery was selected because it was readily available, had good build quality, and had one of the better capacities.

7
When the camera is operated at low horizontal resolutions, the horizontal line readout period is reduced, and there is less time for the sensor's analog-domain correlated double sampling operation to complete. This causes the pixel black levels to be offset upwards, so black comes out as dark grey. This is all invisible to the user, the black calibration corrects for this increased offset automatically, but it does decrease the dynamic range as you mentioned. The offsets are variable across the 32 analog to digital converter (ADC) channels in the image sensor, so different amounts are subtracted from each column.

When the image is saturated to white, the ADCs are all clipped, and so output the same value. When the column offsets are subtracted from this clipped output, it results in this vertical banding you see, since some columns have more subtracted than others. I don't believe there is any significant improvement to be made here unfortunately, it may be possible to have some improvement in a future software update by optimizing the sensor register settings, but it's largely a limitation of the image sensor itself.

To answer your question on homogeneous exposure, if you stay below the point where the vertical banding starts to occur, a homogeneous light pattern illuminating the sensor should result in a homogeneous image output. This is an offset issue only, there should not be any significant variance of gains across columns.

8
The simplest way to remove this is to simply gain up the images enough that the darkest pixels clip to white. You could also use the digital gain option on the record settings screen, but this doesn't have particularly good granularity. Doing it in postprocessing would be the most accurate.

9
Chronos User Discussion / Re: Accuracy of Chronos 1.4
« on: May 26, 2020, 01:43:01 AM »
Hi jbehler,

The frame period is internally quantized on 10ns increments, and the accuracy of the period/frequency is +/- 50ppm based on the internal clock's tolerance.

The exposure time is internally quantized on the image sensor's horizontal line readout period. The exact value is a little bit complicated to calculate, but it's approximately the frame period divided by the frame height in pixels. For example, say your frame period is 1ms (1000fps), and you're at a resolution of 1024 pixels. The horizontal line period is somewhere close to:

0.001 / 1024 = 976.6ns

So the ultimate exposure time will be a multiple of ~976.6ns periods, whichever is closest to the set exposure time.

You can observe this behaviour on an oscilloscope if you set frame sync output on one of the triggers. This signal active when the image sensor is actually exposing.

Let me know if you need any more info.

Cheers!
David

10
Chronos User Discussion / Re: Videos saved but gone
« on: May 26, 2020, 01:01:26 AM »
Hey Martin,

I had thought of a few things to check here, just to cover all bases.

  • Does your eSATA device have multiple partitions on it? If you selected a different partition than expected when selecting the storage device, the file may not be where you expect. If this other partition is something your PC's OS can't see (Like EXT3 from Windows), this other partition may not show up.
  • It is theoretically possible that, due to a bug, the files got saved onto the camera's OS card (microSD in the bottom of the camera), although this shouldn't be allowed by the user interface and underlying API. You could check to see if the files are on the OS card. You'd need to check both the FAT32 and EXT3 partitions that are present on this card.
  • [The d'Oh! one...]Was there any other save media inserted, such as an SD card? Could the files be on that media?

In addition to the file browser, another safety check that could be relatively easily added is to have the API check that the file was successfully written and is a reasonable size, and throw a warning if something doesn't seem right.

David

11
Chronos User Discussion / Re: 1.4 Boot problem
« on: May 12, 2020, 01:30:08 PM »
Does the power LED flash red just before the camera turns itself off? This indicates the PMIC watchdog thinks the main CPU has crashed, and is about to power it down. You might try reflashing the OS card with the latest software, as seen here

12
I would recommend a maximum ambient temperature of 40C. You can check the internal temperature on the About tab in the Util window, as long as the System and Image Sensor temperatures stay under about 70C you should be fine.

The camera has over-temperature protection, it will simply turn off if it gets too hot, but the image quality will degrade slightly while it's hot. The warmer the sensor, the higher the image noise. This isn't permanent, it will go back to normal when it cools down.

David

13
You can use the m2 SSD on the top of the camera and they may not cover the screen

Good idea, did you make a setup using one of these?

14
This is an SSD holder for the Chronos 1.4 and 2.1-HD. This accessory is invaluable when shooting DNG on the go; save speed is vastly improved compared to an SD card. The camera can write about 60MB/s to a SATA SSD instead of ~12MB/s to most SD cards. DNG saves at about 12FPS on the 2.1-HD and about 18FPS on the 1.4, at full resolution.



We plan to offer this for sale in our store eventually, but you can 3D print one right now! The attached models have been updated from the pictures shown, the SD card opening was widened so you can easily grab an SD card with your fingers instead of needing pliers to remove it.

We're in the process of ordering custom versions of the eSATAp cables that have a short cable length to avoid the need to coil up the extra cable.


Items you'll need



3D Printer to print the SSD cage (see attached files)

3D Print Instructions
This file has been tested on the Makerbot Replicator 2X
Recommended settings:
Print with raft, raft expansion 12mm
Print with supports
Orient the part with the drive opening pointing straight up

We've been using these at Krontech for the last few months and these mounts are incredibly useful, let us know how they work for you! One modification we were thinking about is centering the SSD above the camera. Currently, it overhangs the screen and makes it harder to see if you're looking from an upward angle. Thoughts?

15
Chronos User Discussion / Re: Post Chronos 2.1 clips here!
« on: February 17, 2020, 03:14:21 PM »
Had some fun over the long weekend vacuuming sawdust

https://www.youtube.com/watch?v=gXRkDqFwBOY

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