Note, each color space is defined over an extended range, as defined by the referenced CSS definitions,

to represent color values outside of its space (in both chrominance and luminance).

<h4 id=out-of-gamut-premultiplied-rgba-value data-dfn-type=dfn>Out-of-Gamut Premultiplied RGBA Values

<h4 data-dfn-type=dfn>Out-of-Standard-Gamut Color Representation

<span id=out-of-gamut-premultiplied-rgba-value><!-- historical permalink --></span>

</h4>

An [=out-of-gamut premultiplied RGBA value=] is one where any of the R/G/B channel values

exceeds the alpha channel value.

An [=out-of-standard-gamut color representation=] is one where any of the unpremultiplied

red/green/blue channel numeric values are outside of the 0-to-1 range.

In a premultiplied representation, the R/G/B value is outside the 0-to-`alpha` range.

Any numeric value in any gamut is a well-defined "color" according to that gamut's extended

color space (regardless of whether the point represents a real or imaginary color).

That "color" can be represented in other gamuts as well, where it may be in-gamut.

<div class=example>

For example, the premultiplied sRGB RGBA value `[0.52, 0, 0, 0.5]`

represents the (unpremultiplied) color <code><a funcdef>color</a>(srgb 1.04 0 0 / 0.5)</code>.

For example, the unpremultiplied sRGB RGBA value `[1.04, 0, 0, 0.5]` and the

premultiplied sRGB RGBA value `[0.52, 0, 0, 0.5]` both represent the

CSS color <code><a funcdef>color</a>(srgb 1.04 0 0 / 0.5)</code>

which is equivalent to <code><a funcdef>color</a>(display-p3 0.95 0.21 0.15 / 0.5)</code>.

</div>

Just like any color value outside the sRGB color gamut, any value is a well-defined point in the

extended color space (regardless of whether the point represents a real color).

When a canvas containing such a value is

[$get a copy of the image contents of a context|used as an image source$],

thecolor value mustnot be clamped intheimage value given to the calling algorithm

thereturned image mustrepresenttheoriginal color values without clamping,

regardless of the canvas's {{GPUCanvasConfiguration/format}}.

However, when a canvas containing such a value is displayed *on screen*, **if and only if** the

<td>`[0.52, 0, 0, 0.5]`

<td>(undefined result),

<br>because the format is range-limited

<br>and the color is out-of-gamut for {{PredefinedColorSpace/"srgb"}}.

<br>and the color is out-of-standard-gamut for {{PredefinedColorSpace/"srgb"}}.

</table>

The last result is undefined because the color could be:

Note:

Grayscale images generally represent RGB values `(V, V, V)`, or RGBA values `(V, V, V, A)` in their color space.

Colors are not lossily clamped during conversion: converting from one color space to another

will result in values outside the range [0, 1] if the source color values were outside the range

of the destination color space's gamut. For an sRGB destination, for example, this can occur if the

source is rgba16float, in a wider color space like Display-P3, or is premultiplied and contains

[=out-of-gamut premultiplied RGBA value|out-of-gamut values=]. <!-- FIXME? -->

Colors must not be lossily clamped during conversion: converting from one color space to another

may result in an [=out-of-standard-gamut color representation=] in the destination gamut,

which must be preserved. Refer to that section for details.

Similarly, if the source value has a high bit depth (e.g. PNG with 16 bits per component) or

extended range (e.g. canvas with `float16` storage), these colors are preserved through color space

conversion, with intermediate computations having at least the precision of the source.

Similarly, precision must be preserved through color space conversion, with intermediate

computations being at least as precise as the less-precise of the source and destination

(for example copying a PNG with 16 bits per component, or a canvas with `float16` storage, into a

{{GPUTextureFormat/rgba16float}} texture).

### Color Space Conversion Elision ### {#color-space-conversion-elision}

When alpha is 0, no color is represented, regardless of the RGB values.

(Attempting to compute the color results in division by zero.)

In this mode, the canvas texture mayrepresent [=out-of-gamutpremultiplied RGBA values=].

If the canvas has a range-limited format and is displayed on screen, out-of-gamut values

have undefined display results. Refer to that section for details.

In this mode, the canvas texture mayhold [=out-of-standard-gamutcolor representations=].

If the canvas has a range-limited format and is displayed on screen, out-of-standard-gamut

valueshave undefined display results. Refer to that section for details.

</dl>

# Errors &amp; Debugging # {#errors-and-debugging}