Fixed invisible label view in label constructor

[bsekachev]

Motivation and context

Related #5031

Before:

After:

How has this been tested?

Checklist

• I submit my changes into the develop branch
• I have added a description of my changes into CHANGELOG file
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (read github docs)
• I have increased versions of npm packages if it is necessary (cvat-canvas,
  cvat-core, cvat-data and cvat-ui)

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.

[bsekachev]

/check

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[bsekachev]

/check

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[nmanovic]

/check

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[klakhov]

Good job, bright labels are visible now 😃

[klakhov]

What do you think about using something like HSL?

let [r, g, b] = [backgroundColor.slice(1, 3), backgroundColor.slice(3, 5), backgroundColor.slice(5, 7)];
r = parseInt(r, 16) / 255;
g = parseInt(g, 16) / 255;
b = parseInt(b, 16) / 255;
const CMax = Math.max(r, g, b);
const CMin = Math.min(r, g, b);
const lightness = (CMax + CMin) / 2;
if (lightness - 0.85 >= 0) {
      textColor = '#000000';
}

HSL:

RGB variant:

Personally I liked first variant more.