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Invert Layer Contrast Control

By Nick Thomas - United Kingdom

Different methods for controlling image contrast, includes Photoshop actions for download.

With some high contrast images levels and curves adjustments do not yield satisfactory results or require complex masking to apply different degrees of adjustment to different areas of the image.

Using a contrast mask is one possible approach to dealing with contrast. Briefly, contrast masking involves overlaying a colour image with a inverted greyscale image which has been blurred to make a soft mask; for a full description of the process see http://www.luminous-landscape.com/tutorials/contrast_masking.shtml

With practice contrast masking is an excellent approach to taming the contrast range within an image, and with experience can give good results. However one drawback of contrast masking is that the degree of Gaussian blur used to create the mask can make a dramatic difference to the final image. Too little blurring gives an image which looks flat or has unnatural looking edges; too much blurring can lead to contours or haloes of different density at tonal transitions in the image. Since Gaussian blur cannot be applied as an adjustment layer it is difficult to adjust the contrast masking.

After some trial an error I've come up with an alternative method which allows the contrast of an image to be controlled using an adjustment layer and hence allows the degree of contrast control to be adjusted even after the image has been saved.

 

Original image Image after Gaussian blur contrast masking Image after Inverse layer contrast adjustment
 

 

To adjust an image using this method first of all make a copy of the image on a new layer and then desaturate the lower of the two images (Image > Adjust > Desaturate). Create an Invert adjustment layer above the desaturated image and then set the blend mode for the top layer to Hard Light.

Now the colour image on the top layer is interacting with the underlying negative image, and the strength of  the interaction can be controlled by changing the opacity of the Invert layer.

Layers used in invert adjustment
layer contrast control
 

Setting the opacity to 50% has no effect on the image as the underlying greyscale image is converted to a uniform 50% grey. Increasing the opacity from 50% to 100% boosts the amount of inversion being applied to the lower image such that dark tones in the colour image overlay increasingly light tones in the negative image below. This has the desired effect of lightening the dark tones in the colour image; the three images below show the effect of adjusting the Invert layer opacity from 50% (no effect) to 100% (full strength adjustment). Simply experiment with the opacity until you are happy with the image. Since all adjustments have been carried out using layers, files can be saved and re-opened for further adjustment and fine tuning at a later time.

 

Invert  at  50% opacity
Invert  at  75% opacity
Invert  at  100% opacity
 

I've written Photoshop actions for the methods described above which can be downloaded by clicking the link below. Three actions are available; Contrast Mask and Contrast Mask (Adjust Blur) run the Gaussian blur overlay technique (the second action pauses to allow you to set the degree of blur to suit different images if required), Invert Layer Contrast Control runs the alternative new technique used above.

Some of the procedures described in the technical section have Photoshop actions which you can download and use on your own images. To use these actions click on the actions link and save the actions file to your desktop. Open the Photoshop actions palette and click on the menu arrow (circled in red below) and click on 'Load actions...'. Navigate to your desktop, select the actions file and click the load button. Now open the image(s) you want to work on and click the play arrow at the bottom of the actions palette.

Download Contrast Control Actions



Nick ThomasNick Thomas lives in Wales and has been a photographer for 17 years using 35mm and medium format systems. Since buying his first digital camera three years ago Nick’s work has been exclusively digital.

Nick’s current activities concentrate primarily on landscape photography in a variety of environments which can be viewed in the galleries at Land & Sky ( http://www.nickgallery.com/ ).

Nick is an Associate of the Royal Photographic Society.

 

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