Selective desaturation.

Step 1:

Open up your image that you would like to use. I searched on Google with the keyword: Flowers
And i found this picture:

Step 2:

Duplicate the layer (Ctrl + J) and go to Image > Adjustments > Desaturate (Shift + Ctrl + U)

Step 3:

Now we have a black and white picture.

Take out your erase tool, and start erasing on your picture. Feel free to zoom in, this will make it a lot easier.

Now start erasing the parts on your flower you would like to have in color like the example below.


And that's basicly it.

My final result.

I've added some text and a border.

To have such text effect.
Just Type your text in any color you like.
Then Ctrl+click on your text layer.

Now your txt will be selected. Click on your Desaturated layer while your text is still selected and hit your Delete button on your keyboard.
Now you hide your text layer or just delete your text layer. And that's it!

The font that I used is Scriptina.

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