What is the difference between Uint8Array and Uint8ClampedArray in JavaScript?
I understand that Uint8ClampedArray is used with canvas for pixel manipulations. Why is that and what is the benefit?
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1 Answer
Looking at the examples for Uint8ClampedArray and Uint8Array, it looks like the difference is how values are treated when assigned.
If you are trying to set one element to a clamped array to any value outside of the range 0-255, it will simply default to 0 or 255 (depending on whether the value is smaller or larger). A normal Uint8Array array just takes the first 8 bit of the value.
Examples:
var x = new Uint8ClampedArray([17, -45.3]);
console.log(x[0]); // 17
console.log(x[1]); // 0
console.log(x.length); // 2
var x = new Uint8Array([17, -45.3]);
console.log(x[0]); // 17
console.log(x[1]); // 211
console.log(x.length); // 2
7 Comments
dan-man
Note also that
Uint8Array([0.9]) is [0], but Uint8ClampedArray([0.9]) is [1], ie. the clamped version uses rounding, but the basic version uses floor.
Indolering
The OP mentioned this was used for pixel values in the canvas, is this a shortcut for saturated arithmetic?
Tomachi
I think Uint8Array would be faster - unless you were using the clamping features for graphics, which maybe faster in that case.
Ilya
Neither the answer, nor the examples give a clue why and in what cases that behavior of
Uint8ClampedArray could be beneficial.
J-16 SDiZ
@llya These are for image/video/audio process. The main feature is: it never overflow/underflow. When you are trying to increase the brightness in an image: max brightness (255)+1 should give 255, not overflow to zero.
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