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According to mozilla, the second parameter for canvas.toDataURL(1,2) is:

If the requested type is image/jpeg or image/webp, then the second argument, if it is between 0.0 and 1.0, is treated as indicating image quality; if the second argument is anything else, the default value for image quality is used. Other arguments are ignored.

But I can't find anywhere that tells me what the default value actually is.

William T.
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2 Answers2

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According to the spec, it alludes to the default being browser dependant:

The second argument, if it is a number in the range 0.0 to 1.0 inclusive, must be treated as the desired quality level. If it is not a number or is outside that range, the user agent must use its default value, as if the argument had been omitted.

Edit: According to one user the default for Firefox is 0.92.

You can specify the JPEG quality as the second parameter to the toDataURL function. The default quality in Firefox is 0.92 (92%).

And according to this webkit bug report Chrome uses the same.

...Adds a libjpeg-based image encoder for Skia bitmaps. Default encoding quality is 92 to match Mozilla...

Community
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Jarrod
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0

Tested saving canvas content with .webp in chrome and edge with same result showing the quality parameter default value to be 0.8.

Here are results with quality on the left:

default -> 313.65 kB
1 -> 8.29 MB
0.9 -> 0.98 MB
0.8 -> 313.65 kB
0.7 -> 200.63 kB
0.6 -> 160.19 kB
0.5 -> 130.57 kB
0.4 -> 109.31 kB
0.3 -> 91.17 kB
0.2 -> 75.09 kB
0.1 -> 67.78 kB
0 -> 48.71 kB

This makes me think that quality parameter may be optimized for biggest decrease in weight and highest image quality and can be different for other image types.

pmad
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