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Basic Image processing using Photoshop
Exhibition Talk by Len Morris CPAGB
Open the image and assess it.
Example :-IPG5577.jpg - The camera gave it that name.
The image looks promising but
The sky contains no information
It is rather dull
It is sloping!
The figure against the waterfall shows scale but the others are a distraction.
First give it a name and save it in a folder that you want to keep it in. –This will ensure that you have a copy of the original from the camera in the folder you downloaded it should you need to return to it. (I call this folder “archive camera downloads” with sub folders identified by subject and date- I also keep this large folder backed up on a separate drive)
Levels.
Apply levels correction
Photoshop CS2 : Image - Adjustments – Levels
Photoshop Elements v8 Enhance – Adjust lighting – levels
See the histogram below
The left hand side shows the dark tones and the right hand side the light tones. Ideally there should be a hill of light in the mid tones going down to zero at both dark and light ends of the histogram.
With the chosen image we see that the dark tones fall off to zero (just) at the left of the histogram but there is a massive peak of the light tones on the right. This is because of the sky. The problem is that the dynamic range of light is too high for the camera sensor to cope with.
There are several ways of dealing with this but not all of them can be dealt with at the basic training level.
- crop so very little sky shows and it is not a distraction – we will choose this solution
- get a sky from a different photo and put it in place of our sky. Not too difficult with this image but not today!
- Use a technique called High Dynamic Range – definitely an advanced technique
- Take two or three images with very different exposures and combine the using the sky from one and the image from another. This is solution 3 done manually in fact. – Advanced!
- Bin the photo. Most photographers will be reluctant to do this but you need to decide if you need a top class image or a good image of a place you visited as we do here so solution 5 is not for us today.
However ignoring the sky we can make some improvements using levels. Move the right hand white arrow at the base of the histogram a little to the left (input level 210) and the whole image is lighter and the mist from the waterfall shows up better.
The History palette
At this point it is worth noting the “History Palette”
To see it select
Photoshop CS2: check Windows - History
Elements v8 : Window – undo history
In each case a list of the last actions you have performed so you can actually return to that status by simply selecting the level you need to return to.
However it is still worth regularly saving your work as if the PC looses power or hangs up you will loose the history palette information as well as the image state.
Curves
We can improve the contrast of the scene without destroying the dark or light areas using curves
To use these select
CS2: Image – Adjustments – Curves
Elements : - not available but Enhance – Adjust lighting – Shadows/Highlights has a similar effect if used with care.
The curves box shows a plot of light level input (from the file) against light level output (for the new modified image). If you use the cursor and right click you can grab the line in various places and pull it up or down. Up makes the image lighter at that light level you have chosen and down makes it darker. However you will notice that the darkest and lightest points on the curve are fixed and do not move unless you grab the line at those points (don’t in general!)
With our image we will grab the centre and pull it up so that the output (shown in the box) is 152 at input 129. Then grab the line at the ¾ up point and pull it up so output is 220 at input 192.
Finally grab the line at the ¼ point and pull it down so the output is 53 against input 64. If you check and uncheck the “Preview” box you will be able so see the effect that you have had.
For your image you will need to experiment with different shape lines using one two or more grab points to alter the tonal range of your image to suit your taste.
In the case of the Icelandic waterfall you see that the image looks more dramatic and the mist shows better as does the contrast on the green mossy cliff to the left.
However we can do better!
Crop and rotate
You can do this at almost any stage of your processing. I usually do it first but today we will do it now.
The crop tool :- 
Select the crop tool from the tool palette (if that is not showing check – Window – Tools to make it visible and drag it to the side of the screen out of the way of the image if possible.)
When you select it you will see a number of options along a bar at the top of the screen.
The boxes we are interested in are Width, Height and Resolution. If there is any figures in these when you open them select “Clear” to clear them.
When we print we need to print at between 200 and 300 pixels per inch. The higher is best but above 200 will give a presentable print. Suppose you want to print at A4 size which is approximately 29 cm wide by 20 cm high.
Enter 29 cm in the width box
20 cm in the height box
300 in the Pixels/inch box (select pixels/inch from the adjacent drop down menu)
Using the cursor click near the top left of the image and drag the rectangle that appears down to the right. Try to get rid of as much of that awful sky as possible! You can adjust the size by selecting the small squares at the corners of the box.
Put the cursor just outside the box at one corner (top right now) and a rotate symbol appears allowing you to rotate the box so that the image appears straight within it. You can adjust the box size again if required.
Be careful not to let a corner of the selection go out of the image!
You can ensure that the two distracting figures on the right are cropped out but the single figure is left giving scale and interest to the viewer.
Burn and Dodge tools
These tools allow us to make selected areas and tonal range levels of the image brighter or darker as required. This makes the area we worked upon change its localised contrast. It is useful for getting rid of a highlight that is distracting to the edge of an image or improving the local contrast of part of the image.
We are going to improve the river and the waterfall with the mist around it.
Select the Dodge tool
You can change the “brush” size by either selecting the drop down menu “Brush” (“size” in Elements) and modifying the size slider or (much quicker) use the “[“ and “]”keys that change the brush size directly.
Open the Burn tool and in the tool bar at the top set “Range” to Shadows and “exposure” to 3%
Open the Dodge tool and in the tool bar at the top set “Range” to Highlights and “exposure” to 3%
Use a medium sized tool bar for both burn and Dodge move the tool circle over first the river and then the waterfall and mist. Be careful not to overdo the dodge tool on the waterfall so you keep detail in the falls.
If you go to the History pallet and highlight the task prior to your dodge and burn tasks (probably crop) you will be able to see what the image was like before you started. Select the last task in the history and you will return to how it is now.
Put a frame round it. (for Photoshop CS2 only)
It is easy to put a simple frame around your new image.
Make sure that your colour swatches are black foreground and white background
Select – All
Make sure that the black is the foreground swatch.
Edit – Stroke brings up a menu box
Enter 30 px in the Width box,
The colour will be black if your foreground swatch was black
Location – inside
Blending Normal
Opacity 100%
Swap the swatch colours around (select the little double headed arrow)
Repeat Edit – stroke but with 20 px in the Width box
Repeat Edit - stroke again with 12 px in the width box.
You now have a neat black and white border around your image. You can vary this border by choosing different widths and different colours as required.
Sharpen.
This is useful but needs to be applied with care and do not get over enthusiastic. It is not possible to make a blurred image sharp but a sharp one can be improved slightly.
Photoshop CS2 : Filter - Sharpen – Unsharp mask
Photoshop Elements 8 : - Enhance – Unsharp mask
The concept of sharpening is to set values that can just make the sharpening visible when you select the preview tick box. Too much sharpening causes unwelcome artifacts such as small halos around objects and straight edges with a jagged edge formed.
There are various methods
I suggest setting the radius for a 10Mbyte image at about 2.0 pixels or slightly less and the threshold at 3 pixels then adjusting the Amount until the sharpening effect is just visible usually in the range of 30% to 70%
The result.
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Before |
After |
Now what? I would want to do something about the bland sky!