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Hex transparency in colors


Question

I'm working on implementing a widget transparency option for my app widget although I'm having some trouble getting the hex color values right. Being completely new to hex color transparency I searched around a bit although I couldn't find a specific answer to my question.

I want to set transparency by hex color so let's say my hex color id "#33b5e5" and I want it to be 50% transparent. Then I'll use "#8033b5e5" because 80 is 50%.

I found a useful chart here: http://www.dtp-aus.com/hexadeci.htm . With this data I managed to come up with this:

0% = #00
10% = #16
20% = #32
30% = #48
40% = #64
50% = #80
60% = #96
70% = #112
80% = #128
90% = #144

Now the issues start appearing when I get higher than 100 in hex. Hex color codes can only be 8 symbols long right? For example #11233b5e5 (80%) crashes.

What can I do to enable me to use the higher numbers aswell?

2018/08/10
1
1293
8/10/2018 3:14:07 PM

Accepted Answer

Here's a correct table of percentages to hex values. E.g. for 50% white you'd use #80FFFFFF.

  • 100% — FF
  • 95% — F2
  • 90% — E6
  • 85% — D9
  • 80% — CC
  • 75% — BF
  • 70% — B3
  • 65% — A6
  • 60% — 99
  • 55% — 8C
  • 50% — 80
  • 45% — 73
  • 40% — 66
  • 35% — 59
  • 30% — 4D
  • 25% — 40
  • 20% — 33
  • 15% — 26
  • 10% — 1A
  • 5% — 0D
  • 0% — 00

(source)

2017/05/23
3714
5/23/2017 12:18:27 PM

Short answer

You can see the full table of percentages to hex values and run the code in this playground in https://play.golang.org/p/l1JaPYFzDkI .

Short explanation in pseudocode

Percentage to hex values

  1. decimal = percentage * 255 / 100 . ex : decimal = 50*255/100 = 127.5
  2. convert decimal to hexadecimal value . ex: 127.5 in decimal = 7*16ˆ1 + 15 = 7F in hexadecimal

Hex values to percentage

  1. convert the hexaxdecimal value to decimal. ex: D6 = 13*16ˆ1 + 6 = 214
  2. percentage = (value in decimal ) * 100 / 255. ex : 214 *100/255 = 84%

More infos for the conversion decimal <=> hexadecimal

Long answer: how to calculate in your head

The problem can be solved generically by a cross multiplication.

We have a percentage (ranging from 0 to 100 ) and another number (ranging from 0 to 255) then converted to hexadecimal.

  • 100 <==> 255 (FF in hexadecimal)
  • 0 <==> 0 (00 in hexadecimal)

For 1%

  • 1 * 255 / 100 = 2,5
  • 2,5 in hexa is 2 if you round it down.

For 2%

  • 2 * 255 / 100 = 5
  • 5 in hexa is 5 .

The table in the best answer gives the percentage by step of 5%.

How to calculate the numbers between in your head ? Due to the 2.5 increment, add 2 to the first and 3 to the next

  • 95% — F2 // start
  • 96% — F4 // add 2 to F2
  • 97% — F7 // add 3 . Or F2 + 5 = F7
  • 98% — F9 // add 2
  • 99% — FC // add 3. 9 + 3 = 12 in hexa : C
  • 100% — FF // add 2

I prefer to teach how to find the solution rather than showing an answer table you don't know where the results come from.

Give a man a fish and you feed him for a day; teach a man to fish and you feed him for a lifetime

2020/05/17

Color hexadecimal notation is like following: #AARRGGBB

  • A : alpha
  • R : red
  • G : green
  • B : blue

You should first look at how hexadecimal works. You can write at most FF.

2013/04/06

That chart is not showing percents. "#90" is not "90%". That chart shows the hexadecimal to decimal conversion. The hex number 90 (typically represented as 0x90) is equivalent to the decimal number 144.

Hexadecimal numbers are base-16, so each digit is a value between 0 and F. The maximum value for a two byte hex value (such as the transparency of a color) is 0xFF, or 255 in decimal. Thus 100% is 0xFF.

2014/09/11

I built this small helper method for an android app, may come of use:

 /**
 * @param originalColor color, without alpha
 * @param alpha         from 0.0 to 1.0
 * @return
 */
public static String addAlpha(String originalColor, double alpha) {
    long alphaFixed = Math.round(alpha * 255);
    String alphaHex = Long.toHexString(alphaFixed);
    if (alphaHex.length() == 1) {
        alphaHex = "0" + alphaHex;
    }
    originalColor = originalColor.replace("#", "#" + alphaHex);


    return originalColor;
}
2014/06/24

enter image description here

This might be very late answer. But this chart kills it.

All percentage values are mapped to the hexadecimal values.

http://online.sfsu.edu/chrism/hexval.html

2020/04/19