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fix typo - thanks peter luft

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zschuessler committed Nov 11, 2016
1 parent c8f5cb4 commit 5ca41bb24390b799ec2ca322fbc399ca1c9596ec
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@@ -18,7 +18,7 @@ <h2>Introduction</h2>
<p>
The <a href="http://www.cie.co.at/index.php/LEFTMENUE/About+us">International Commission on Illumination</a>
(<em>CIE</em>) formed in the early 1900s to standardize the fields of
- colorimetry, photometry, and imaging. The commission addressed the
+ colorimetry, photometry, and imaging. The commission addressed the
topic of color difference in 1976, introducing the world to the concept
of Delta E.
</p>
@@ -33,52 +33,52 @@ <h2>Defining Delta E</h2>
ΔE - (<em>Delta E, dE</em>) The measure of change in visual perception of two given colors.
</p>
<p>
- Delta E is a metric for understanding how the human eye perceives color
- difference. The term <em>delta</em> comes from mathematics, meaning change in
- a variable or function. The suffix <em>E</em> references the German word
+ Delta E is a metric for understanding how the human eye perceives color
+ difference. The term <em>delta</em> comes from mathematics, meaning change in
+ a variable or function. The suffix <em>E</em> references the German word
<em>Empfindung</em>, which broadly means sensation.
</p>
<p>
On a typical scale, the Delta E value will range from 0 to 100.
</p>
<table>
<tbody>
- <tr>
+ <tr>
<th>Delta E</th>
<th>Perception</th>
</tr>
- <tr>
+ <tr>
<td><= 1.0</td>
<td>Not perceptible by human eyes.</td>
</tr>
- <tr>
+ <tr>
<td>1 - 2</td>
- <td>Perceptible through close observation.</td>
+ <td>Perceptible through close observation.</td>
</tr>
- <tr>
+ <tr>
<td>2 - 10</td>
<td>Perceptible at a glance.</td>
</tr>
- <tr>
+ <tr>
<td>11 - 49</td>
<td>Colors are more similar than opposite</td>
</tr>
- <tr>
+ <tr>
<td>100</td>
<td>Colors are exact opposite</td>
</tr>
</tbody>
</table>
<p>
Take the table as a general guide; it’s possible to get a Delta E
- value below 1.0 for two colors that appear different. This is
+ value below 1.0 for two colors that appear different. This is
the case with CIE76 and CIE94 formulas, in which saturation is
either not considered or not weighted properly.
</p>
<p>
- Because of inconsistencies between the three algorithms, the
+ Because of inconsistencies between the three algorithms, the
exact meaning of Delta E changes slightly depending on which
- formula is used. Think of Delta E less as a definitive answer,
+ formula is used. Think of Delta E less as a definitive answer,
and instead a helpful metric to apply to a specific use case.
</p>
@@ -99,7 +99,7 @@ <h3>Delta E 76</h3>
<figure>
<img src="{{ site.baseurl }}/img/formula-cie76.png" alt="CIE76 color difference formula" title="CIE76 color difference formula" />
<figcaption>The first-ever Delta E</figcaption>
-</figure>
+</figure>
<p>
Look familiar? Indeed, you're looking at a ripoff of the <a href="http://en.wikipedia.org/wiki/Euclidean_distance">Euclidean Distance</a>
formula. This makes sense, as CIELAB color space was created as a 3D
@@ -108,34 +108,34 @@ <h3>Delta E 76</h3>
<figure>
<img src="{{ site.baseurl }}/img/lab-space.png" alt="LAB color space distance example" title="LAB color space distance example" />
<figcaption>Two points in LAB color space</figcaption>
-</figure>
+</figure>
<p>
Alas, issues are afoot. The premise that LAB color space is
- perfect in perceptual uniformity falls short, particularly with
- differences in saturation. The example above demonstrates that
+ perfect in perceptual uniformity falls short, particularly with
+ differences in saturation. The example above demonstrates that
for hues in the same lightness it works well. But what happens
when we have two saturated colors of different hues?
</p>
<figure>
<img src="{{ site.baseurl }}/img/lab-space-2.png" alt="LAB color space distance comparison example" title="LAB color space distance comparison example" />
<figcaption>Two very different hues, highly saturated</figcaption>
-</figure>
+</figure>
<figure>
<img src="{{ site.baseurl }}/img/lab-swatch-comparison.png" alt="LAB color swatch comparison" title="LAB color swatch comparison" />
<figcaption>
A closer comparison of the two colors above. Are they similar?
<br/>
...indeed - they appear to be!
</figcaption>
-</figure>
+</figure>
<p>
- The two above blocks represent the dark blue and dark red as
+ The two above blocks represent the dark blue and dark red as
graphed. CIE76 reports this difference as ΔE 10 (<em>perceptible at a glance</em>),
when by definition difference should fall in the ΔE~1-3 range
(<em>perceptible with close observation</em>).
</p>
<p>
- Clearly saturation is a major problem for dE76. In the below
+ Clearly saturation is a major problem for dE76. In the below
example, blue highlights pixels that each algorithm has
determined as 25% within tolerance of pure saturation (black).
</p>
@@ -146,17 +146,17 @@ <h3>Delta E 76</h3>
</figcaption>
</figure>
<p>
- Delta E can mean different things for a given use case. Here,
+ Delta E can mean different things for a given use case. Here,
if we wanted to come closer to matching all black color in CIE76,
we would pad the Delta E number more. (<em>Note this lends to
more error, as tolerance increases.</em>)
</p>
<p>
So when do we still use CIE76? The formula has the major advantage
- of being a simple Euclidean Distance calculation: it’s faster
- than the successive CIE formulas. It’s used in
- performance-intensive situations that don’t require high
- accuracy. Image processing and real-time post processing
+ of being a simple Euclidean Distance calculation: it’s faster
+ than the successive CIE formulas. It’s used in
+ performance-intensive situations that don’t require high
+ accuracy. Image processing and real-time post processing
of media is an example of where CIE76 would suffice.
</p>
<p>
@@ -166,9 +166,9 @@ <h3>Delta E 76</h3>
<!-- Delta E 94 -->
<h3>Delta E 94</h3>
<p>
- In 1994, the original Delta E formula was improved. The new
+ In 1994, the original Delta E formula was improved. The new
formula would take into account certain weighting factors for
- each lightness, chroma, and hue value. It also introduced the
+ each lightness, chroma, and hue value. It also introduced the
ability to add a modifier according to the use case: either
textile, or graphic arts.
</p>
@@ -178,15 +178,15 @@ <h3>Delta E 94</h3>
<figure>
<img src="{{ site.baseurl }}/img/formula-cie94.png" alt="CIE 94 formula" title="CIE 94 formula" />
<figcaption>
- dE76 Formula
+ dE94 Formula
</figcaption>
</figure>
<p>
CIE94 introduced a conversion of the given Lab value into
- CIE L*C*h (Lch). The two color models differ in that Lch
+ CIE L*C*h (Lch). The two color models differ in that Lch
represents hue as an angle instead of infinite points of color.
- This allows us to more easily troubleshoot and perform
+ This allows us to more easily troubleshoot and perform
calculations on hue.
</p>
<figure>
@@ -206,22 +206,22 @@ <h3>Delta E 94</h3>
</figcaption>
</figure>
<p>
- Given the two colors above, we can agree that the two are much
+ Given the two colors above, we can agree that the two are much
different in hue, but similar in overall lightness. CIE94
calculates ΔE 128 (<em>polar opposites</em>), while CIE2000 more
correctly calculates ΔE 49.4 (<em>middle of the road</em>).
</p>
<p>
CIE94 is very much Baby Bear in Goldilocks lore: It’s a middle of
- the road formula where accuracy is necessary but not mission-critical.
+ the road formula where accuracy is necessary but not mission-critical.
It’s still often used in textiles and printing applications today.
</p>
<!-- CIE2000 -->
<h3>Delta E 2000</h3>
<p>
The CIE organization decided to fix the lightness inaccuracies
- by introducing dE00. It’s currently the most complicated,
+ by introducing dE00. It’s currently the most complicated,
yet most accurate, CIE color difference algorithm available.
</p>
<figure>
@@ -232,7 +232,7 @@ <h3>Delta E 2000</h3>
</figure>
<p>
All this busy work gets us a more accurate lightness calculation.
- We can see the difference in saturation weighting below.
+ We can see the difference in saturation weighting below.
This graph compares dE94 and dE00 in posing the question,
"Is pure green more similar to white or black?"
</p>
@@ -243,13 +243,13 @@ <h3>Delta E 2000</h3>
</figcaption>
</figure>
<p>
- Bravo for dE00, which maintains the correct weighting as
+ Bravo for dE00, which maintains the correct weighting as
lightness fades from black to white. The formula concludes color
difference between green/black and green/white is moderate.
</p>
<p>
dE94 incorrectly concludes that black/green has roughly the same
- color difference as white/green. It’s almost as if it couldn't
+ color difference as white/green. It’s almost as if it couldn't
weight saturation properly!
</p>
<figure>
@@ -259,16 +259,16 @@ <h3>Delta E 2000</h3>
</figcaption>
</figure>
<p>
- Although the most accurate we have today, dE00 is not without
+ Although the most accurate we have today, dE00 is not without
fault. The most significant discontinuity occurs when compared
- hues are 180° from each other (forcing a hue shift in the calculation).
+ hues are 180° from each other (forcing a hue shift in the calculation).
According to a <a href="http://www.ece.rochester.edu/~gsharma/ciede2000/ciede2000noteCRNA.pdf">Rochester CIE2000 Analysis paper</a>,
this could create a discontinuity of ΔE 0.2734. For all but the
most high accuracy use cases, this is negligible.
</p>
<p>
- Remember: Delta E accuracy must be confirmed through the very
- tool it was meant to remove subjectivity from -
+ Remember: Delta E accuracy must be confirmed through the very
+ tool it was meant to remove subjectivity from -
<em>a pair of human eyes.</em>
</p>
@@ -278,16 +278,16 @@ <h3>References</h3>
(2014). Retrieved from http://www.cie.co.at/
</li>
<li>
- Sharma, G. (2004). The CIEDE2000 Color-Difference Formula:
- Implementation Notes, Supplementary Test Data, and Mathematical
- Observations. Retrieved from
+ Sharma, G. (2004). The CIEDE2000 Color-Difference Formula:
+ Implementation Notes, Supplementary Test Data, and Mathematical
+ Observations. Retrieved from
<a href="http://www.ece.rochester.edu/~gsharma/ciede2000/ciede2000noteCRNA.pdf">
http://www.ece.rochester.edu/~gsharma/ciede2000/ciede2000noteCRNA.pdf
</a>
</li>
<li>
- Color Differences & Tolerances: Commercial Color Acceptability.
- (2013, January 1). Retrieved from
+ Color Differences & Tolerances: Commercial Color Acceptability.
+ (2013, January 1). Retrieved from
<a href="http://industrial.datacolor.com/support/wp-content/uploads/2013/01/Color-Differences-Tolerances.pdf">
http://industrial.datacolor.com/support/wp-content/uploads/2013/01/Color-Differences-Tolerances.pdf
</a>
@@ -306,7 +306,7 @@ <h3>References</h3>
var $toc = $('.post-content_toc').toc({
container: '.post-content'
});
-
+
// show toc only after title is in view
var triggerOffset = $('.post-content').offset().top;
var currentOffset;

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