Databases
StackOverflow2013
Postsdbo
POHow can I convert an RGB image to grayscale but keep one color?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POHow can I convert an RGB image to grayscale but keep one color?
    primarykey
    data
    text
    <p>I am trying to create an effect similar to <em>Sin City</em> or other movies where they remove all colors except one from an image.</p> <p>I have an RGB image which I want to convert to grayscale but I want to keep one color.</p> <p>This is my picture:</p> <p><img src="https://i.stack.imgur.com/EcyOd.jpg" alt="alt text"></p> <p>I want to keep the red color. The rest should be grayscale.</p> <p>This is what my code outputs so far (you can see that the areas are correct, I don't know why they are white instead of red though):</p> <p><img src="https://i.stack.imgur.com/22O60.jpg" alt="alt text"></p> <p>Here is my code so far:</p> <pre><code>filename = 'roses.jpg'; [cdata,map] = imread( filename ); % convert to RGB if it is indexed image if ~isempty( map ) cdata = idx2rgb( cdata, map ); end %imtool('roses.jpg'); imWidth = 685; imHeight = 428; % RGB ranges of a color we want to keep redRange = [140 255]; greenRange = [0 40]; blueRange = [0 40]; % RGB values we don't want to convert to grayscale redToKeep = zeros(imHeight, imWidth); greenToKeep = zeros(imHeight, imWidth); blueToKeep = zeros(imHeight, imWidth); for x=1:imWidth for y=1:imHeight red = cdata( y, x, 1 ); green = cdata( y, x, 2 ); blue = cdata( y, x, 3 ); if (red &gt;= redRange(1) &amp;&amp; red &lt;= redRange(2) &amp;&amp; green &gt;= greenRange(1) &amp;&amp; green &lt;= greenRange(2) &amp;&amp; blue &gt;= blueRange(1) &amp;&amp; blue &lt;= blueRange(2)) redToKeep( y, x ) = red; greenToKeep( y, x ) = green; blueToKeep( y, x ) = blue; else redToKeep( y, x ) = 999; greenToKeep( y, x ) = 999; blueToKeep( y, x ) = 999; end end end im = rgb2gray(cdata); [X, map] = gray2ind(im); im = ind2rgb(X, map); for x=1:imWidth for y=1:imHeight if (redToKeep( y, x ) &lt; 999) im( y, x, 1 ) = 240; end if (greenToKeep( y, x ) &lt; 999) im( y, x, 2 ) = greenToKeep( y, x ); end if (blueToKeep( y, x ) &lt; 999) im( y, x, 3 ) = blueToKeep( y, x ); end end end imshow(im); </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USPeter O.
    1. USRichard Knop
    plurals
    1. This table or related slice is empty.
    1. PL
      singulars
      1. LTLinked
    2. PL
      singulars
      1. LTLinked
    3. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POHow can I convert an RGB image to grayscale but keep one color?
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POHow can I convert an RGB image to grayscale but keep one color?
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POHow can I convert an RGB image to grayscale but keep one color?
      1. This table or related slice is empty.
      1. VTUpMod
    1. COIt seems Matlab is providing a solution but it would be interesting to see a code golf of this...
      singulars
      1. POHow can I convert an RGB image to grayscale but keep one color?
      1. USgary
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload