digital graduated ND filter

Discussion in 'Graphics Programs and Photo Gallery' started by pursuer, Apr 28, 2005.

  1. pursuer

    pursuer TPF Noob!

    Aug 8, 2004
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    One problem faced when shooting landscapes is the large dynamic range of the scene. If you expose for the foreground the sky becomes blown out, if you expose for the sky the result is a foreground that is too dark. So you you comprimise and end up with a sky and foreground that are not quite as good as they could be. Probably the best solution to this problem is the use of a graduated netral density filter to reduce the brightness of the sky and bring it closer to that of the foreground. However if you are like myself and do not own such a filter you might find this tutorial useful.

    I will show you how create the equivalent of a digital graduated ND filter using photoshop. I will be using photoshop CS although I believe any version of PS will be able to acomplish this. I will use an image that was captured as a JPEG but this method will of course work even better with RAW images.

    Here is the original image:

    The first step is to create a new level adjustment layer:

    Name the layer or leave it as the default "levels 1", It dosn't really matter.

    Now use the histogram to adjust the sky to the desired brightness, ignoreing the forground.
    the histogram for this image has two distinct peaks, one represents the values in the sky and the other represents the values in the foreground. I have positioned the black point at the foot of the slope that represents the sky. Now the sky is looking better but the foreground is much too dark.
    By useing an adjustment layer instead of just adjusting the levels we can use a layer mask to control which areas of the image are darkened.

    notice in the layers window that there are two boxes in the adjustment layer.
    The first has a black and white circle, double clicking this would allow you to change the histogram again. The second box, the one with the arrow is the layer mask. Picture the layer mask superimposed over the background image, where ever the mask is white the adjustment layer will darken the background image, where ever the mask is black the image will not be affected at all. Shades of gray are in between.

    right now the mask is completly white so the image is darkened equally all over.

    hold down the "ALT" key and click the layer mask box, (the one with the arrow pointing to it)

    The image should have turned completely white. You can now edit the actual layer mask, but first we need a second window so we can see the effect changing the layer mask has on the image in real time.

    Do the following:

    You should now have two windows, a white one containing the layer mask and another displaying the background image.

    select the gradient tool, it is on the same button as the paint bucket. press "d" on the keyboard to reset the palete colors to the default black and white (just in case). In the layer mask window drag the gradient tool from the bottom to the top of the window to create a gradient like the following:


    An immediate effect can be seen on the background image, it is looking better but we still need to do a level adjustment on the gradient by going to Image --> adjustments --> levels

    after the adjustment my layer mask looks like this:
    It now more closely matches the background image.

    The next step is to right click on an empty space on the level adjustment layer and select "duplicate layer"

    You should now have something similar to the above.
    Notice the little eyes next to each layer. click on the eye indicted by the arrow and it should disapear. That layer is now hidden (we will need it later).

    You now have two layers that are not hidden (still have eyes), click on one of them so it becomes active (blue).

    now goto "Layers --> Merge visable" this will combine the layers while ignoreing the hidden layer.

    Now that the sky has been darkened we need to lighten the foreground. Unhide the copy of the level adjustment layer by clicking where the eye used to be. Hold down "ALT" and click the box for the layermask. You should now see the gradient, hold down "CTRL" and press "i" this will invert the layer mask so the level adjustment layer affects the foreground instead of the sky.

    Now double click the box with the black and white circle and adjust the histogram to lighten the foreground, you may want to do an additional level adjustment to the gradient if nessecary. Now goto Layers --> flatten image and you're done :)


  2. Fadi

    Fadi TPF Noob!

    Apr 8, 2005
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    Alexandria VA
    Nice job... :thumbup:

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