# Identify head and tail of the fish

**URL:** <https://forum.opencv.org/t/identify-head-and-tail-of-the-fish/5337>\
**Category:** Python\
**Tags:** imgproc\
**Created:** [September 23, 2021, 10:36am UTC](https://forum.opencv.org/t/identify-head-and-tail-of-the-fish/5337 "2021-09-23T10:36:00Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![crackwitz](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.opencv.org/crackwitz/32/14_2.png) [@crackwitz](https://forum.opencv.org/u/crackwitz)\
**Post date:** [September 23, 2021, 12:36pm UTC](https://forum.opencv.org/t/identify-head-and-tail-of-the-fish/5337/2 "2021-09-23T12:36:24Z")

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different tasks:

#### calibration

- intrinsic camera calibration (projection matrix, lens distortion)
- extrinsic calibration (camera–surface pose): put a checkerboard or ARUCO/CHARUCO in frame

assuming the fish is flat and on the surface, now you can get physical lengths from the picture.

#### segmentation

use a different color for the background. the fish itself appears white in parts. use a color that will certainly not appear on the fish.

threshold to get a mask.

#### next

> [@Image of fish, how to find these points of contour?](https://forum.opencv.org/t/can-someone-tell-me-how-to-find-these-points-of-contour/5184):
>

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