The Histogram Adjustment Tool
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PSP Ver. 7 Tutorial |
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In the main menu bar, under Colors, Histogram Functions, you will find the Histogram Adjustment Tool. The window displays the distribution of intensities in the image's Luminosity. It runs from pure lack on the left to pure white on the right. By looking at the graph, you can determine how to adjust your image to optimize its contrast and bring out more detail without loss of important information.
The photo below is a scanned image from a magazine. The image is well balanced and thus will allow for improvements. How do I know this? (see the tutorial on the Histogram)
Looking at the graph, we can see that there is a gap between the left edge of the window and the point where the graph begins to rise. Similarly, there is a gap between he right edge of the window and the point where the graph ends. We want these to be the upper and lower clipping limits for the image.
To do this, we slide the black triangle to the right until it is directly below where the graph starts and the white triangle to the left at the point where the graph ends.
The intensities at the two locations are shown in the boxes labeled Low and High. The lower clip limit and everything below this limit will be set to black. The higher clip limit and everything above it will be set to white. The boxes below the Low and High values indicate what percentage of the pixels will be affected.
The preview windows above the graph show the image in its original state and how the new settings will change it. The clipping limits that were selected have greatly improved the overall glow.in the face and hair and have given the imag new life.
As a finishing touch, I used the Effects, Noise, Edge Preserving Smooth command to keep the detail in the edges and add a little smoothnes to the face
What do you think?
Not bad for a scanned image.
ACTUALLY that's great for a scanned image.
Selective Adjustment
Sometimes, adjusting the entire image at once is not the answer. A change in contrast can reduce color saturations. This is especially true when there is sky in the photograph. Look at the imge below.of the New York Skyline. We would like to add detail to the buildings and the water but we want the blue in the sky to remain blue... .
We start by first selecting the sky and the water and the inverting the selection to limit it to the buildings and rocks. The Magic Wand tool is perfect for this.
We can see in the Histogram Adjustment window that the graph looks strange at best. However, in keeping with our discussion above, we still want to set the clipping limits for the image.
I left the lower limit at zero (0) and positioned the white triangle at a point where the graph peaks. In this particular case the high limit was set to 194. Directly below the limit box we can see that roughly 28% of the pixels will be affected.
To the right of the graph there is a slider for adjusting the midtones. Moving the slider up will give you more detail in the dark areas and moving it down will give you more detail in the bright areas. I set the slider to -10. The preview window showed me the effect.
Notice how the detail in the buildings has been brought out.
After the image was corrected, I selected the water again and repeated the operation. The results are shown below. The one on the right is what I saw in real life. I think you will agree the Histogram Adjustment is a powerful tool in your arsenal of tools for photo enhancement. .
