[css-color-hdr] Explain where the eps factor comes from, and what it is for #11788

Author: svgeesus

css-color-hdr-1/Overview.bs

@@ -126,6 +126,12 @@ WPT Display: open
 			"abstract": "This standard specifies an EOTF characterizing high-dynamic-range reference displays used primarily for mastering non-broadcast content. This standard also specifies an Inverse-EOTF derived from the EOTF.",
 			"isbn": "978-1-61482-829-7"
 		},
+		"SMPTE-ST-2094-50": {
+			"href": "https://github.com/SMPTE/st2094-50",
+			"title": "Dynamic Metadata for Color Volume Transform - Application #5 (Broadcast)",
+			"publisher": "SMPTE",
+			"date": "2025"
+		},
 		"What_is_ICtCp": {
 			"href": "https://professional.dolby.com/siteassets/pdfs/ictcp_dolbywhitepaper_v071.pdf",
 			"title": "What is ICtCp, v7.1",
@@ -611,7 +617,7 @@ Mixing Dynamic Range Limits: the ''dynamic-range-limit-mix()'' function {#dynami
 	by multiplying each color component by 203 [[Rpt_BT.2408]]
 	to convert from relative units (Y of white is 1, regardless of actual brightness)
 	to absolute units of cd/m², also called "nits".
-	In the <a href="#scolor-conversion-code">sample code</a>,
+	In the <a href="#color-conversion-code">sample code</a>,
 	this constant is denoted <var ignore=''>Yw</var>,
 	the luminance of HDR Reference White.
 
@@ -637,11 +643,16 @@ Mixing Dynamic Range Limits: the ''dynamic-range-limit-mix()'' function {#dynami
 	3. Let <var> w1</var> = clamp((<var>H</var> - <var>H2</var>) / (<var>H1</var> - <var>H2</var>), 0, 1)
 	4. Let <var> w2</var> = clamp((<var>H</var> - <var>H1</var>) / (<var>H2</var> - <var>H1</var>), 0, 1)
 		Note that <var> w2</var> = 1 - <var> w1</var>
-	5. Let <var>eps</var> = 0.001 (one JND in linear-light space)
+	5. Let <var>eps</var> = 0.001
 	6. Let <var>cxyz</var> = Array(3)
 	7. For i from 0 to 2:
 		Let <var>cxyz</var>[i] = pow(<var>c1xyz</var>[i] + <var>eps</var>, <var>w1</var> ) * pow(<var>c2xyz</var>[i] + <var>eps</var>, <var>w2</var> ) - <var>eps</var>
 
+	Note: The factor <var>eps</var> is to prevent division by zero,
+	and the value is chosen to match that used in
+	[[SMPTE-ST-2094-50]].
+
+	
 	<div class="example" id="ex-hdr-interpolate">
 	For example, given c1 = color(rec2100-linear 0.9 1.0 0.8),
 	c2 = color(rec2100-linear 1.8 2.0 1.5),