* bug#14074: 24.3.50; Convert hsv to rgb
2013-03-28 14:56 bug#14074: 24.3.50; Convert hsv to rgb Jambunathan K
2002-01-01 0:41 ` Jambunathan K
@ 2013-04-07 13:37 ` Jambunathan K
1 sibling, 0 replies; 3+ messages in thread
From: Jambunathan K @ 2013-04-07 13:37 UTC (permalink / raw)
To: 14074
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(Check my copyright assignment status before applying the patch provided
in my earlier mail.)
Jambunathan K <kjambunathan@gmail.com> writes:
> Convert hsv to rgb.
Here are a few additions/enhancements to color.el and facemenu.el that
would be useful. These suggestions are based on an prototype that I
built.
----------------------------------------------------------------
M-x suggest-colors RET
======================
To get a feel for the proposed
M-x suggest-colors RET
see the attached screenshots, particulary one named
copy-of-suggest-colors-use-pure-color.png. The only difference between
the two screenshots is that one works off the base/pure color while the
other works off the given color.
See next section for additional comments.
----------------------------------------------------------------
Table of Contents
─────────────────
1 Enhancements to color.el
2 Enhancements to facemenu.el
3 Add M-x suggest-colors RET
1 Enhancements to color.el
══════════════════════════
1. Clarify difference between rgb and srgb. (Frankly, I don't know
the difference.)
Here are some references found.
1. [http://debbugs.gnu.org/cgi/bugreport.cgi?bug=8402]
2. [http://www.w3.org/Graphics/Color/sRGB.html]
Audit the usage of "srgb" in `color-lab-to-srgb',
`color-lab-to-srgb' etc and check whether the terms rgb (#rrggbb)
to srgb are used consistently.
See also note on Item 7.
2. Rgb to hsv conversion
╭────
│ (defun color-hsv-to-rgb (h s v))
╰────
3. Add two colors
╭────
│ (defun color-add-hsl-or-hsv (h s v-or-l δh δs δv-or-δl))
╰────
Use `color-lighten-hsl', `color-saturate-hsl' & co. can be
re-written to use this API.
4. Mod/Round-off a color, for use with (2) above
╭────
│ (defun color-mod (value value-max))
╰────
The function will use modulo operation - C-h f mod. Contrast this
with `color-clamp'.
5. APIs to rotate a color
╭────
│ (defun color-rotate-hsl-or-hsv (H S L-OR-V degrees))
│ (defun color-rotate-name (name degrees))
╰────
6. Get base or pure color (I am not sure about the terminology)
╭────
│ (defun color-pure-color (name))
╰────
This API may not be needed.
7. API for computing relative luminance of a given color.
╭────
│ (defun color-relative-luminance (name))
╰────
Quoting from [http://www.w3.org/TR/WCAG20/]
╭────
│ relative luminance
│
│ The relative brightness of any point in a colorspace, normalized to 0
│ or darkest black and 1 for lightest white
│
│ Note 1: For the sRGB colorspace, the relative luminance of a color is
│ defined as L = 0.2126 * R + 0.7152 * G + 0.0722 * B where R, G and B are
│ defined as:
│
│ * if RsRGB <= 0.03928 then R = RsRGB/12.92 else R = ((RsRGB+0.055)/1.055) ^ 2.4
│ * if GsRGB <= 0.03928 then G = GsRGB/12.92 else G = ((GsRGB+0.055)/1.055) ^ 2.4
│ * if BsRGB <= 0.03928 then B = BsRGB/12.92 else B = ((BsRGB+0.055)/1.055) ^ 2.4
│
│ and RsRGB, GsRGB, and BsRGB are defined as:
│
│ * RsRGB = R8bit/255
│ * GsRGB = G8bit/255
│ * BsRGB = B8bit/255
│
│ The "^" character is the exponentiation operator. (Formula taken from [sRGB] and [IEC-4WD]).
│
│ Note 2: Almost all systems used today to view Web content assume sRGB
│ encoding. Unless it is known that another color space will be used to
│ process and display the content, authors should evaluate using sRGB
│ colorspace. If using other color spaces, see Understanding Success
│ Criterion 1.4.3.
╰────
Additional note: In `list-colors-sort-key' (search for luminance),
above linear relation for L is being used, without the associated
conditional checks suggested above.
8. An API for computing luminosity contrast ratio between two colors.
╭────
│ (defun luminosity-contrast-ratio (name1 name2))
╰────
This will help in selecting a foreground and background colors
(presumably non-grey) which provide sufficient contrast.
See [http://www.w3.org/TR/WCAG20/#contrast-ratiodef].
╭────
│ 1.4.3 Contrast (Minimum): The visual presentation of text and images
│ of text has a contrast ratio of at least 4.5:1, except for the
│ following: (Level AA)
╰────
2 Enhancements to facemenu.el
═════════════════════════════
1. Enhance M-x display-colors RET to *also* show hsv value.
Currently hsv values are shown as tooltip. The format specifier
for printing the hsv values is *really not that useful*.
See attached screenshots.
2. Indicate darkness or lightness of the color (based on value of
relative luminance).
Useful to quickly settle on white or black as a contrasting color.
3. Add "Sort by contrast (against a chosen color)" to C-h v
list-colors-sort RET.
This can be used to find colors (presumably non-grey) that will
contrast nicely with given color.
4. Refactor `list-colors-display'.
M-x `list-colors-display' does two things - sorting and displaying.
I find that the displaying part is awkwardly split between this
routine and `list-colors-print'. (Note that the *Help* buffer
generated in the former and displaying done in the later. This is
not very useful in practice.)
So, split `list-colors-display' to say `sort-colors' and
`display-colors'.
5. Find a color name that is nearest to a given numeric color.
╭────
│ (defun nearest-color (color))
╰────
A naive implementation would return, for example,
╭────
│ (car (sort-colors list-of-colors)) ; pseudo-code
╰────
6. Use the standards based `color-cie-de2000' to compute differences
between colors and do away with `hsv-dist' and `rgb-dist'.
Currently, sorting by `hsv-dist' uses Euclidean distance over
cylindrical co-ordinates. My little experimentation shows that
`hsv-dist' as it is defined is satisfactory for finding the nearest
color name to a given numericla color.
`rgb-dist' distance is less than satisfactory in some edge cases.
So, it's claim that it is closer to human perception is a bit
questionable.
7. Re-think `color-gradient' in terms of color scheme (see next
section)
╭────
│ (defun color-gradient (start stop step-number)
╰────
May be use a hsv or hsl based scheme rather than a rgb based scheme
for computing gradients.
3 Add M-x suggest-colors RET
════════════════════════════
This command can provide following options. Note that each of these
sets is generated by doing a "set of deltas" to the base color.
1. complements :: Color that is 180° apart
╭────
│ complement(c) = c + [180°, 0, 0]
╰────
1. split complements :: Colors that are on either side of a
complementary color
╭────
│ split complement(c) = {c, c + [180°-δdeg, 0, 0], c + [180°+δdeg, 0, 0]}, δdeg = 30°
╰────
1. triads :: Colors that are 120° apart
╭────
│ triads(c) = {c, c + [120°, 0, 0], c + [240°, 0, 0]}
╰────
2. tetrads :: Colors that are 90° apart
╭────
│ tetrads(c) = {c, c + [90°, 0, 0], c + [180°, 0, 0], c + [270°, 0, 0]}
╰────
3. Analogous :: Colors that are equidistant and closer to a given
color.
╭────
│ analogous(c) = {c, c + [30°, 0, 0], c + [-30°, 0, 0]}
╰────
4. Monochromatic :: Colors having same hue but different saturation
and value. (Tint, tone and shade etc)
╭────
│ mono(c) = {c, c + [0°, 0.3, 0], c + [0°, 0, 0.3], c + [0°, 0.3, 0.3]}
╰────
See [Color theory] which explains how [Color scheme designer] could be
made use of.
Interestingly, the above designer provides different sets of
monochrome colors. Vary choice of "Preset" menu and examine how
Adjust schemes->Adjust variants to see how the monochrome deltas are
located in s,v plane.
[Color theory] http://www.w3.org/wiki/Colour_theory
[Color scheme designer] http://colorschemedesigner.com/
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