TDA4VE-Q1: CAC module’s input LUT

Ding Y

Part Number: TDA4VE-Q1

Dear TI experts,

When we use the CAC function, we are asked to enter a four-column LUT. However, the VPAC3 help documentation does not have instructions on how to obtain LUT as in the LDC module. Also, it is unclear what the different lines in LUT represent. May I ask how we need to obtain this Lut form? May I ask you to help me with the above problems?

over 2 years ago

0 Gang Hua over 2 years ago

TI__Guru 59340 points

Hi Ding,

You should have the LUT format details from the plugin guide.
There is a typo of "S8U3" which should be S8Q3 (same as in LDC).

The first 2 columns and last 2 columns are same as LDC LUT in specifying the R and B shifts respectively.

You will have to obtain the CA information from your lens vendor or calibrate your lens on your own in order to create the CAC LUT similar to LDC.

0 Ding Y over 2 years ago in reply to Gang Hua

Prodigy 245 points

Hi Gang，

Can you provide the MATLAB code for generating LUT? In addition, lens vendor is unable to provide detailed CA information. What are your suggestions for customizing LUTs? Note: We address the issue of purple circles near image highlights.

Thank you in advance for your time.

+1 Gang Hua over 2 years ago in reply to Ding Y

TI__Guru 59340 points

Hi Ding,

I don't have matlab code for generating the LUT and I don't have much experience in calibrating CA.

In general, you will have to find a way (S/W or a 3rd party) to calibrate CA of your lens so that you have the information about the relative R and B shift to G as a radial LUT similar to LDC distortion table.
Then, you may modify the LDC matlab code slightly to generate the LUT for R and B separately before putting them together.

0 li quan over 2 years ago in reply to Ding Y

Intellectual 955 points

Hi Ding,

Now I have met the same problem with you. How did you solve it at last? How did the input LUT generate?

Looking forward your reply!

0 Ding Y over 2 years ago in reply to li quan

Prodigy 245 points

Hi Quan,

I modified the matlab script used to generate the LDC LUT. The modified script can process the chromatic aberration data from the lens manufacturer to generate the LUT required by the CAC.

0 li quan over 2 years ago in reply to Ding Y

Intellectual 955 points

Hi Ding,

Thank you very much for your reply! But, could you please share your source code with me? I asked relevant colleagues and it seems that we don't have the source code for LDC generating either.

Best !

0 Gang Hua over 2 years ago in reply to li quan

TI__Guru 59340 points

LDC code is in the FAQ -- https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1058565/faq-tda4vm-how-to-create-a-ldc-mesh-lut-for-fisheye-distortion-correction-on-tda4?keyMatch=LDC%20FAQ

0 Ding Y over 2 years ago in reply to li quan

Prodigy 245 points

Hi quan，

Have you ever encountered the problem of purple edge changing to blue edge when using cac? And what is the minimum downsampling factor you used there?

Best regards,

0 Gang Hua over 2 years ago in reply to Ding Y

TI__Guru 59340 points

I believe we are discussing this on an separate thread.

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TDA4VE-Q1: CAC module’s input LUT