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The source-quality attribute gives the quality of the variant, as a representation of the negotiable resource, when this variant is rendered with a perfect rendering engine on the best possible output medium.

source-quality 属性は、その変種が可能な最善の出力媒体に完璧なレンダリング円陣でレンダリングした時における折衝可能資源の表現としてのその変種の品質を与えます。

If the source-quality is less than 1, it often expresses a quality degradation caused by a lossy conversion to a particular data format. For example, a picture originally in JPEG form would have a lower source quality when translated to the XBM format, and a much lower source quality when translated to an ASCII-art variant. Note however, that degradation is a function of the source; an original piece of ASCII-art may degrade in quality if it is captured in JPEG form.

source-quality が 1 以下であれば、 しばしば特定データ書式への損失変換によって起こる品質低下を表します。 例えば、元々 JPEG 形であった絵は XBM 形式に翻訳した時に低い原典品質を持つこととなりますし、 ASCII絵変種に翻訳した時には更に低い原典品質を持つこととなります。 しかし、この品質低下は原典の関数であることに注意してください。 元々 ASCII 絵のものを JPEG 形で撮影したら品質は落ちるかもしれません。

The source-quality could also represent a level of quality caused by skill of language translation, or ability of the used media type to capture the intended artistic expression.

source-quality は、 言語翻訳の能力による品質の水準をも表現することができますし、 意図した芸術的表現を撮影した使用されている媒体型の能力を表現することもできます。

Servers should use the following table a guide when assigning source quality values:

サーバーは、原典品質値を割当てる時に、次の表を手引きとして使うべきです。

1.000	perfect representation
0.900	threshold of noticeable loss of quality
0.800	noticeable, but acceptable quality reduction
0.500	barely acceptable quality
0.300	severely degraded quality
0.000	completely degraded quality

The same table can be used by local variant selection algorithms (see appendix 19) when assigning degradation factors for different content rendering mechanisms. Note that most meaningful values in this table are close to 1. This is due to the fact that quality factors are generally combined by multiplying them, not by adding them.

When assigning source-quality values, servers should not account for the size of the variant and its impact on transmission and rendering delays; the size of the variant should be stated in the length attribute and any size-dependent calculations should be done by the variant selection algorithm. Any constant rendering delay for a particular media type (for example due to the startup time of a helper application) should be accounted for by the user agent, when assigning a quality factor to that media type.