Author Topic: Question regarding resolution and frame rate  (Read 323 times)

vinalv

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Question regarding resolution and frame rate
« on: June 25, 2019, 04:56:12 AM »
Hi,
The default minimum resolution is 336x96 which gives 38565 fps.
I have noticed that I can take it down to 192x96 and maintain the same fps.
Now when I change resolutions, always keeping the product of the width (x) and height (y) less than 32256 (which is 336x96) I keep getting frame rates below 38565. Such as 256x124 gives 30230 fps.

Is it possible to maintain the maximum fps of 38565 and follow the above rule of any resolution combo of xy less than 32256?

My aim is to record at the maximum frame rate but either is a square resolution or in a verticale slit. To clarify the resolution 336x96 would be a horizontal slit.

Thanks for any help.

NiNeff

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Re: Question regarding resolution and frame rate
« Reply #1 on: June 25, 2019, 07:54:03 AM »
As far as I'm aware this is not possible since the image sensor is read out in rows. Each row takes its time and substituting columns for rows while keeping the total pixel amount constant does not bring benefits, it instead slows down.
You can use the minimum horizontal size you need for the shot and then crop it afterwards to get square-ish images.

foobar

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Re: Question regarding resolution and frame rate
« Reply #2 on: June 25, 2019, 08:50:41 AM »
NiNeff is correct, the image sensor digitizes an entire row at once and then reads it out 16-pixels at a time to the FPGA. While the first row is being read out to the FPGA, the second row of the image can then be digitized. The time that it takes to digitize a row can be adjusted by playing with the timing parameters of the image sensor but reducing the time allowed for this operation causes a loss of image quality.

The fastest framerate at any resolution is achieved when the row readout time is equal to the row digitization time, so that we minimize the time that the image sensor is idle. And the best quality is achieved when the row readout time is long enough to allow for the maximum digitization timing (approximately 922us per row).

On the 0.3.1 release of the Chronos 1.4, the fastest row digitization time is approximately 255us, which is equal to the time it takes to read out 336 pixels. This is why there is no performance benefit to reducing the horizontal resolution below 336 pixels. On the 0.3.2 release we have managed to reduce this time to 244us, which is why we now list 320x96 as the minimum resolution for that release.

vinalv

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Re: Question regarding resolution and frame rate
« Reply #3 on: June 25, 2019, 09:02:14 AM »
Thank you both for the help

BiduleOhm

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Re: Question regarding resolution and frame rate
« Reply #4 on: June 25, 2019, 11:07:38 AM »
If you want a vertical band while retaining the max framerate you can rotate the camera 90 and correct the rotation in post prod.

vinalv

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Re: Question regarding resolution and frame rate
« Reply #5 on: June 25, 2019, 12:48:33 PM »
Nice idea! Thanks