# Special FX, Duotone

Once you have mastered the greyscale effect, you are 95% of the way there with duotone. This effect is essentially a tinted greyscale, which means that we average the red, green, and blue values then add or subtract a little from each of them to get a particular tint. In order to handle the tint values, our function needs to accept four parameters: the image, a red amount, green amount, and blue amount. There is one additional check to be made for each colour, and that is that it is not over 255 - the maximum value for a single colour. Here is the new function:

``````function duotone (&\$image, \$rplus, \$gplus, \$bplus) {
\$imagex = imagesx(\$image);
\$imagey = imagesy(\$image);

for (\$x = 0; \$x <\$imagex; ++\$x) {
for (\$y = 0; \$y <\$imagey; ++\$y) {
\$rgb = imagecolorat(\$image, \$x, \$y);
\$red = (\$rgb >> 16) & 0xFF;
\$green = (\$rgb >> 8) & 0xFF;
\$blue = \$rgb & 0xFF;
\$red = (int)((\$red+\$green+\$blue)/3);
\$green = \$red + \$gplus;
\$blue = \$red + \$bplus;
\$red += \$rplus;

if (\$red > 255) \$red = 255;
if (\$green > 255) \$green = 255;
if (\$blue > 255) \$blue = 255;
if (\$red < 0) \$red = 0;
if (\$green < 0) \$green = 0;
if (\$blue < 0) \$blue = 0;

\$newcol = imagecolorallocate (\$image, \$red,\$green,\$blue);
imagesetpixel (\$image, \$x, \$y, \$newcol);
}
}
}
``````

The first half of that is basically identical to our greyscale function, but note that the new function takes \$rplus, \$gplus, and \$bplus to handle users passing in tinting information. Now, when the colours are average, the value is stored in \$red. The \$green variable is then set to the value of \$red plus the \$gplus, which is the green tint amount passed into the function. The same is done for blue, with \$blue and \$bplus.

Finally, the \$red variable itself is changed to reflect the red tint amount, then a new colour is allocated based upon these three and the pixel is coloured in with imagesetpixel().

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