TDA3XEVM: What function do I use to achieve global tone mapping?

Amer Naseem

Part Number: TDA3XEVM

Our image sensor is Vanadium Oxide(VOx) Resistive Microbolometers Infrared Thermal Detectors Focal Plane Array(FPA).
Our application is night vision. It's a hunting application. Our product is RifleScope.

FPA output is 14-bit, raw, 640 x 480, monochrome, High Dynamic Range(HDR), it's not companded. It's continuously calibrated to retain HDR, uniformity, etc.

Since 14 bit input data isn't accepted by Image Signal Processor(ISP), TI experts suggested to perform global tone mapping using either Piece Wise Linear(PWL) or LUT (curve defined by lut)
based mapping to tone map to 12 bits.
Once data is tone mapped to 12 bits, I can select ISSM2MISP_LINK_OPMODE_1PASS_WDR mode in ISP.

Also, I was informed that global tone mapping is very similar to gamma compression. Are they similar because they both have a function? Global tone mapping has LUT but gamma correction
doesn't have LUT.

Global tone mapping algorithms range from basic functions (logarithm, power function, sigmoid) to more sophisticated ones that are image dependent. Which algorithm do I need, basic
function or image dependent?

There is information on the internet for tone mapping to match the dynamic range of the scene to that of the display device. This is tone mapping from HDR to Low Dynamic Range(LDR).
But my end goal is to tone map from HDR to HDR?

How do I come up with global tone mapping function and LUT? What information will be in LUT? How to use information in LUT? Is this dependent on my application dependent or image
dependent?

over 6 years ago

0 Amer Naseem over 6 years ago

Expert 1380 points

My primary question is about coming up with a function to achieve global tone mapping from 14-bit to 12-bit.

There are basic global tone mapping functions such as logarithm, power function, sigmoid. Will one of these work for me or I need a more sophisticated image dependent or image sensor dependent function?

Also, what is my end goal? I don't think my end goal is to compensate for display characteristics because this happens near the end of image processing pipeline. I don't think my goal is to approximate the Human Visual System(HVS) non-linearity, or to render visually more appealing images. All these are important steps in image processing but that is not the goal of my special global tone mapping task.

I believe my end goal is that 12-bit global tone mapped video signal matches 14-bit video as close as possible? 12-bit should remain HDR?

0 Mayank Mangla over 6 years ago in reply to Amer Naseem

TI__Mastermind 24525 points

1-Pass WDR flow internally does global tone mapping also. You can specify the tone map function through a look up table. One example of a LUT generated using 0.5 power function is

x = (0:512)*8;

exp = 0.5

y = int(4096 * (pow (x/2^14, exp) ))

0 Amer Naseem over 6 years ago in reply to Mayank Mangla

Expert 1380 points

>> 1-Pass WDR flow internally does global tone mapping also
Is it the GLBCE block that does global tone mapping? How many bits are input to GLBCE? Does GLBCE input accept monochrome data?

0 Mayank Mangla over 6 years ago in reply to Amer Naseem

TI__Mastermind 24525 points

GLBCE can do it but it is used for more complex local tone map. In TI software, Global tone map is done on IPIPEIF.

0 Amer Naseem over 6 years ago in reply to Mayank Mangla

Expert 1380 points

My understanding is as follows?
1. I'll input 14-bits into IPIPEIF.
2. I'll provide global tone map function in a LUT
3. TI SDK will use LUT to global tone map 14 -> 12 bits

Regards,

Amer

0 Mayank Mangla over 6 years ago in reply to Amer Naseem

TI__Mastermind 24525 points

Yes, that's right.

0 Amer Naseem over 6 years ago in reply to Mayank Mangla

Expert 1380 points

Is following 1-Pass WDR flow internal global tone mapping?
Global Brightness and Contrast Enhancement(GBCE).

Is it in ISS Usecase, 1 CH ISS capture + ISS ISP + ISS LDC + VTNF + Display ?
Please provide the flow of this internal global tone mapping code and filenames.

Regards,

Amer

0 Mayank Mangla over 6 years ago in reply to Amer Naseem

TI__Mastermind 24525 points

The usecase is correct. You will need to go into ISS settings and enable 1-pass WDR. Default is linear.

0 Amer Naseem over 6 years ago in reply to Mayank Mangla

Expert 1380 points

I would like to go through TI software that is doing global tone mapping at IPIPEIF.

Currently, my settings are as follows:

PROCESSOR_SDK_VISION_03_05_00_00\vision_sdk\apps\src\rtos\usecases\iss_capture_isp_simcop_display\chains_issIspSimcop_Display.jpg shows my usecase. which link(s) contain code for global tone mapping.

The output of Leopard Imaging Camera is 12-bit pixels in Bayer Format. Where in code are these frames coming into IPIPEIF? Please point to code that is doing global tone mapping.

Regards,

Amer

0 Amer Naseem over 6 years ago in reply to Amer Naseem

Expert 1380 points

What will be the size of LUT? 2^14 or 2^12

0 Mayank Mangla over 6 years ago in reply to Amer Naseem

TI__Mastermind 24525 points

LUT size is 512.

0 Mayank Mangla over 6 years ago in reply to Amer Naseem

TI__Mastermind 24525 points

LUT size is 512

0 Amer Naseem over 6 years ago in reply to Mayank Mangla

Expert 1380 points

In the example function or LUT above, x is input to TI global tone mapping SW? y is output of TI global tone mapping SW?

Regards,

Amer

0 Mayank Mangla over 6 years ago in reply to Amer Naseem

TI__Mastermind 24525 points

The function I specified helps to generate the LUT for decmpanding, which is one part of global tone map. This maps a 12-bit input to 14/16/20-bit input. Atter decompanding, you will need to apply a gamma curve and map down to 12-bit to finish the global tone map

0 Amer Naseem over 6 years ago in reply to Mayank Mangla

Expert 1380 points

>> This maps a 12-bit input to
but my thermal image sensor output is 14-bit

0 Mayank Mangla over 6 years ago in reply to Amer Naseem

TI__Mastermind 24525 points

That's no problem. You can generate the decompanding LUT to handle 14-bit too. The output however, must be 12-bit.

0 Yordan Kamenov over 6 years ago in reply to Mayank Mangla

TI__Mastermind 42515 points

Hi Amer,

We haven't heard back from you, I'm assuming you were able to resolve your issue.
If not, just post a reply below (or create a new thread if the thread has locked due to time-out).

Regards,
Yordan

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TDA3XEVM: What function do I use to achieve global tone mapping?