Image Correction (Printable PDF Version)

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Maanually Adjusting the Tonal RangeThe tonal range of an image represents the amount of contrast, or detail, in the imageand is determined by the image’s distribution of pixels, ranging from the darkestpixels (black) to the lightest pixels (white). We will now correct the photograph’scontrast using the Levels command.In this section, we’ll use a graph in the Levels dialogue box that represents the rangeof values (dark & light) in the image. This graph has controls that adjust the shadows,highlights and midtones (or gamma) of the image. We will also refer to the Histogrampalette, which displays this information for you. Unless you’re aiming for a specialeffect, the ideal histogram extends across the full width of the graph, and the middleportion has fairly uniform peaks and valleys, representing adequate pixel data in themidtones..1.Choose Window > Histogram, or click theHistogram tab in the Navigator palette groupto make the Histogram palette visible. Thenchoose Expanded View from the Histogrampalette menu..2.Choose <strong>Image</strong> > Adjustments > Levels to openthe Levels dialogue box..3.Make sure that the Preview check box isselected, and then move the dialogue box (ifnecessary) so that you can also see the <strong>Image</strong>window and Histogram palette.The left (black) triangle below the histogramrepresents the shadows, the middle (grey)triangle represents the midtones (or gamma)and the right (white) triangle represents thehighlights. If your image had colours acrossthe entire brightness range, the graph wouldextend across the full width of the histogram.Notice that at this point the graphs in the Levelsdialogue box and the Histogram palette areidentical..5.
Maanually Adjusting the Tonal Range.4.In the Levels dialogue box, drag the laft triangleto the right to the point where the histogramindicates that the darkest colours begin.As you drag, the first Input Levels value (abovethe histogram graph) changes and so does theimage itself. In the Histogram palette, the leftportion of the graph now stretches to the edgeof the frame. This indicates that the darkestshadow values have shifted closer to blackNote: You can also scrub to change the InputLevels value: First click in the text box for thevalue you want to change, and then drag thepointer over the Input levels label..5.Drag the right triangle to the left to the pointwhere the histogram indicates that the lightestcolours begin. Again, notice the changes in thethird Input Levels value, in the image itself, andin the Histogram palette graph..6.Drag the middle triangle a short distance to theleft side to lighten the midtones.Watch the changes in the image window and inthe Histogram Palette graph to determine howfar to drag the middle triangle..7.When the image looks good to you, click OK toapply the changes. Then save your work..6.
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Image Correction (Printable PDF Version)

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