Technical Deep Dive

Pick the 3-5 sections most relevant to the role. Keep it conversational.

1 Imaging pipeline (15 min)

Choose appropriate questions from the following:

Camera Overview

“Walk me through what happens when a user takes a picture on a live-view camera.”

Follow-ups

• Issues you’ve seen in V4L2?
• Which ISP stages would you implement first and why? (see pipeline checklist)

ISP Blocks

Can you explain the components shown in this ISP diagram?

Q: Can you walk through the pipeline? A:

• MIPI
• FPN (Fixed Pattern Noise)
• BLC (Black Level Correction)
• AWB (Auto White Balance)
• Gain
• DPCC (Defective Pixel Correction)
• AE (Auto Exposure)
• AF (Auto Focus)
• Hist (Histogram)
• HDR-Merge (High Dynamic Range)
• Bayer 2DNR & 3DNR
• LSC (Lens Shading Correction)
• HDR DRC (HDR Dynamic Range Compression, includes tone mapping)
• GIC (Green Imbalance Correction)
• Debayer
• CCM (Colour Correction Matrix)
• Gamma
• Dehaze enhance
• 3D LUT
• LDCH (Lens Distorsion Correction Horizontal)
• CSM (R2Y) (Colour Space Matrix, RGB to YUV)
• YUV 422
• Sharpener
• CGC
• FIFO
• SCL (Scaler)
• MI-WR (Memory Interface WRite)

Q: Prioritise the order in which these would be implemented and why and how do they influence the image quality. A:

Image review

This image was taken during the bring up of the IPU3 through libcamera.

We were happy that we had images flowing through the pipeline - but what things can you see that are wrong with this image and what would you do to improve them?

(We're looking for a realisation that the White balance is wrong visible from the green roof, and the image is overexposed visible from the white shirts).

2 Embedded Linux (10 min)

• Can you build a kernel from source?
• Experience with U-Boot / TFTP / NFS-root?
• How would you add code to a running kernel?
• Can you describe the differences between I2C / SPI / UART?
  • When would you use each one ?
• What happens when your C code performs a read or write to a register?

3 Multimedia & Codecs (10 min)

• What’s a pixel format? Who defines FourCCs?
• Explain the difference between raw Bayer and YUV 4:2:2.
• What’s a codec? Name one lossless and one lossy example.

4 Open-source contribution (5 min)

• Have you submitted patches via e-mail before?
• Show me one commit you’re proud of - what problem did it solve?

5 Workflows and Coding (xxx min?)

Can you describe your work environment please?

• How familiar are you with Git, could you explain a git interactive rebase?

What work have you done with C++?

• Can you explain a shared pointer ?
• What does object orientation mean to you ?
• What happens when calling a virtual function?

6 Problem-solving scenario (up to 20 min)

“A user reports small oscillations in image brightness.”

How would you diagnose and fix this?

Look for: clarifying questions, tooling choice, systematic approach.

7 Systems thinking (fun open challenge)

“What happens when a user double-clicks an icon on the desktop?”

Let them roam from input event → compositor → kernel → storage → scheduler.

8 Soft Skills

Assume you're stuck for two days - what do you do ?

• Did you have any conflicts at work - and how did you solve or handle them ?
• What about if you've implemented something but your manager or project lead wants it done differently? How do you solve this conflict ?
• What do you expect from your project lead or manager ?

Scoring rubric (1–5)

Add scores inline in your notes; average later.