imx8mp Embedded ISP Gamma encoding

取消
显示结果 
显示  仅  | 搜索替代 
您的意思是: 

imx8mp Embedded ISP Gamma encoding

488 次查看
malik_cisse
Senior Contributor I

Hello,

Our images look good, but I don't quite understand a factual situation regarding the gamma. The ISP seems to be applying gamma correction even though it is explicitly turned off.

I don't quite understand where the gamma encoding should come from. Maybe you can help me here.

The following points are known:

  • The image sensor (Sony IMX477) delivers linear image data.
  • Gamma decoding in the ISP (degamma) is programmed to pass-through (see XML): input array == output array.
  • Gamma encoding in the ISP is turned off (see XML: gc enable="false").
  • The ISP-CCM was set to the identity matrix and AWB was turned off. Manual WB was set to 1,1,1,1 (pass-through).
  • Gamma decoding of 2.2 is applied in the LCD display controller (implemented in the kernel driver).

The black values are correctly reproduced both from the LCD live images and from the YUYV snapshots (directly after the embedded ISP), which means that a gamma must have been set in the ISP.

However, since this is turned off, I don't understand where the gamma comes from?

Thx, M.Cisse

0 项奖励
回复
2 回复数

466 次查看
malik_cisse
Senior Contributor I

Hi,
Thank you for the quick feedback.

>>No gamma encoding is supported by ISP you better check your camera is causing the gamma encoding.
This statement might be correct for the software software ISP (SW-ISP). I am referring to the i.MX8M-Plus embedded ISP which definitely has deGamma (or sensor linearization) as well as Gamma encoding (also referred in the xml ISP config file as "gc enable").

The whole point using the i.MX8M-Plus is to avoid the SW-ISP.
But thank you for trying to help.
Cheers

0 项奖励
回复

469 次查看
Bio_TICFSL
NXP TechSupport
NXP TechSupport

Hello,

No gamma encoding is supported by ISP you better check your camera is causing the gamma encoding.

https://www.nxp.com/docs/en/application-note/AN12060.pdf

Regards

0 项奖励
回复