refactor(Watermark): update background size check logic

[ArgoZhang]

update background size check logic

Summary of the changes (Less than 80 chars)

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Description

fixes #5136

Regression?

• Yes
• No

[If yes, specify the version the behavior has regressed from]

[是否影响老版本]

Risk

• High
• Medium
• Low

[Justify the selection above]

Verification

• Manual (required)
• Automated

Packaging changes reviewed?

• Yes
• No
• N/A

☑️ Self Check before Merge

⚠️ Please check all items below before review. ⚠️

• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
• Merge the latest code from the main branch

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (6980608) to head (2a9b94e).
Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #5137      +/-   ##
===========================================
+ Coverage   99.98%   100.00%   +0.01%     
===========================================
  Files         634       634              
  Lines       28181     28181              
  Branches     4040      4040              
===========================================
+ Hits        28177     28181       +4     
+ Misses          4         0       -4     

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