I would like to know how I can make the gradient tool aligned perpendicular to a line in photoshop, or how to set the exact angle of the gradient? I know that by pressing the Shift key, I can constrain the angle of the gradient tool to increments of 45 degrees, but let's say for example in the following photo, I want to create a layer mask to mask out the sky and the water, but I want the bottom part of the layer mask to be a gradient from the horizon to the water. How can I align the gradient exactly to the horizon line?

enter image description here

  • Rotate the image slightly so the horizon is level, then there will be no problem.
    – Billy Kerr
    Jun 3, 2018 at 14:25

1 Answer 1


Quick selection of the sky, some images with hard contrast allow to make a quick selection from a channel.

In this case, from the Channel window > duplicating the Blue Channel > Menu Image > Adjustments > Levels > eliminate midtones moving shadows and lights to the center.


A square frame at the bottom filled with black cover the sea. Selecting the sky with the Magic Wand > Invert selection > Fill it with black.

For fine retouching with the Brush Tool, visualize the RGB channel clicking on the eye icon or/and change the new channel opacity


This is the SKY/SEA Channel.

Activate the RGB channel > with the Shape tool, choose Line, 6px weight, and make a line shape layer across the horizon from side to side of the file (green on the image):


From the Layers Window > Hide the background layer.

With the Magic Wand click on the bottom area below the green line to select the sea and keep the selection.

With the Shape Selector Tool > Select the line > Copy > Paste > Transform > Rotate 90º


Channel Window > Activate the SKY/SEA Channel clicking on the name > Make the RGB channel visible clicking on the eye to see the vertical line


Choose the Gradient Tool > From Black to Transparent, make a gradient line from the bottom to the horizon following the vertical green line.

line 1

To make the other version, duplicate the SKY/SEA channel and using the same selection > Menu Image > Adjustments > Invert


Layers Window > Duplicate the background image

Menu Select > Load Selection... > Choose SKY/SEA or SKY/SEA COPY and apply the mask:




  • I originally meant option B, but I would be interested in knowing how to do both if there is a big difference between the two methods
    – shmth
    Jun 4, 2018 at 22:54

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