In this tutorial, we will teach you how to remove tan lines in Photoshop. For this tutorial, we will be working on a free stock image which can be downloaded from the following link:
stockfreeimages com/5479749/Park-Portrait.html
Notice in the image, that the tan lines are quite visible. So download the image, bring it in Photoshop and let's get started with removing these tan lines.

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Step 1 -- Changing the Image Color Mode
First of all, you will need to change the image color mode to Lab Color. For that, move over to the Image menu on top, hover over the Mode option and select the Lab Color option from the menu that opens up.

Step 2 -- Making a selection of the tan area
With that done, pick up the polygonal lasso tool from the menu on the left and carefully make a selection around the tan lines on the skin. Make sure that you follow the exact pattern of the tan lines from top to bottom.

Step 3 -- Using the Levels Adjustment layer
With the selection active, move over to the Layers panel and open up the adjustment layer menu by clicking on the button, highlighted in the image below. From the menu, select the Levels Adjustment option. Notice that this automatically creates a new layer with the area of the selection masked within the layer. From this point onwards, whatever changes you make will only be applied to the masked area, that is, the tanned area on the skin.
For this tutorial, we have used a non-destructive method for adding the effects to this image. To revert the changes all you have to do is either remove the mask, or if you want to start all over again, just delete the adjustment layer. This way, the original image is kept intact. On the other hand, if you use the spot healing brush tool, the original texture of the image gets ruined and no matter how efficiently you might use the tool, there will remain irregular midtones and highlights. So working with adjustment layers is a very good alternative.

Step 4 -- Sampling different shades on the skin
Moving on, head back towards the menu on the left, open up the eyedropper tool menu by pressing the option and once the new menu opens up, select the Color sampler tool. This will help us sample the darker and lighter shades of the skin tone so that we can identify and make changes accordingly.
So hover over the darker portion of the skin tone and click over there to grab the color sample. You can press the F8 key on the keyboard to open up the info panel. This would help you see the readings on the samples you would be taking. You can see in the highlighted are in the image below that the first sample is already showing there. Next, you can use this tool to grab a lighter tone so that later you can make the lighter tone the same as darker tone.

Step 5 -- Configuring Channel A, B and Lightness
Now we will use the different channels in the levels adjustment layer to effectively remove tan lines in Photoshop. For that, open up the levels adjustment panel and select the "a" channel from the drop down menu. This is to equalize the colors a bit. With that done, increase the midrange to match the reading of the second sample. Notice that as you adjust the midtones, the values of the "CHANNEL A" in the info panel keeps on changing. Notice in the image, that when we set the value to 1.30, the values of both the samples match. You will also notice that as you change the values, the selection starts to blend in with the skin tone a bit.
With that taken care of, now select the channel "b" from the list. This channel will control the yellows and the blues in the image. We have set the midpoint to 1.05 and moved the white point, or the highlights, inwards a bit, setting the value to 254.
Once you are done with both these channels, open up the lightness channel and increase the darkness so that it matches with the skin tone. For this tutorial, we have set the shadows, or the black arrow on the left, to 2, midrange to 0.77 and highlights to 254 for the input levels. You can experiment with different values according to the image you are working on.

Step 6 -- Masking off the sharp edges
Now close the adjustment panel and the info panel and move to the toolbar on the left to pick up the brush tool. Next, use the brush tool to mask out the sharp edges of the levels adjustment layer and blend it with the skin tone. Make sure you use a soft brush for this purpose and keep the opacity of the brush below 40%. Before applying the brush, you have to keep the foreground color to black and the background color to white. This way, when you start applying the brush, the area will be masked off accordingly.

The rest of the lesson is in this video.