Levels & Curves

(Article by Peter)

Levels & Curves

Select – Image > Adjustment > ………)

Levels and curves are used to increase or reduce the over all brightness within a photograph and to adjust the picture appearance based on black, grey and white points or to Red, Gree or Blue. Both Levels and Curves are selected, once a photograph has been opened, from the - Image > Adjustments list of options.

Levels. -  Image >Adjust > Levels. (Preview should be ticked).

Using the Channel dropdown list levels can be applied to Red, Green & Blue colours in your picture individually or all at the same time.  I suggest you leave it at the RGB setting unless you wish to correct a particular colour tint within the picture.

1)   For a quick fix initially click on Auto, this allows Photoshop to adjust your photo as it thinks best. (Same as Image > Adjust > Auto Levels from dropdown list. The Auto Levels settings can be adjusted by selecting Options.

2)   The three eye droppers adjust the levels within the Photo based on Black, Grey and White.      

Select the desired eyedropper with a left mouse click, point the dropper nozzle at a section of your image that is known to be white, grey or black and left click, Photoshop will adjust the levels of the picture accordingly.

3.   The little triangle pointers under the histogram and graded scale (Input and Output) can be dragged left or right to change the levels.

4.   Again use the left mouse button to select the pointer, for Input, moving the right hand pointer to the left increases the overall brightness, moving the left hand pointer to the right darkens it.  The output pointers work in reverse.4The Levels can be applied to the individual Red Green and Blue channels within your photo if one of these hues need to enhanced or reduced, take care this can produce really odd results to the photo.

Curves - Image >Adjust > Curves. (Preview should be ticked).

Curves perform a similar function as Levels, to some extent it is a matter of ones preference which tool you use.  Again the curves can adjust only the individual Red Green and Blue element within your photo, or all at the same time, I suggest you leave the Channel set to RGB.  The changes are made permanent after Save has been selected, Cancel will revert the photo to its original state prior to a Save, Edit > Undo reverses the previous change that has been made to the photo.

1. Curves has an Auto button that works in a similar way to Levels, again Options adjusts the Auto Colour correction.
2. Curves have the nose droppers to set the colours balance within your photo to a known white, grey and black selected object. Select the desired dropper with a left mouse click, point the nozzle to a known white, grey or black part of the picture and left click on the mouse.
3. To manually adjust the colour curve for your photo, ensure the little sign wave button is selected, place your mouse pointer over the graph region and it will change to a small cross. Place the cross at any point on the diagonal graph line and left click, this will lock that part of the curve. By default the shades vertical and horizontal run from dark to light from the bottom left of the curve.  Now holding down the left mouse button warp the curve upwards to make the photo lighter and warp it downwards to make it darker. By selecting different set points on the curve, individual light and dark areas can be enhanced within the photo.  I suggest you experiment, but do not save, provided preview is ticked, your changes can be seen as you make them, once you are happy with your changes Save the curve.

The curve can be applied to the individual Red Green and Blue channels within your photo if one of these hues need to enhanced or reduced, take care this can produce really odd results to the photo.