Despite the pursuit of the sharpest lenses and the best resolutions we can get , digital cameras will not produce a sharp image. Until recently when the OLPF ( Optical Low pass Filter ) was used in the camera , to deliberately blur images , so as to correct later in post processing the misalignment from adjoining pixel sites across the image .
However this also benefitted images that were resized , because resizing “interpolates “ extra pixels into the image and the need to be aligned for production of hard copies.
Most cameras will allow you to sharpen images in camera , however this is not a good idea as it can limit the usage and create image degradation .If the images are to be used straight away such as Event photography where we are producing a one shot size image for customers on the spot this is an acceptable use …
In terms of technology , CCD sensors produce sharper images straight put of the camera which is why most medium format systems still use CCD sensors whereas DSLR Cameras are virtually all using CMOS sensors .
Many cameras now have no optical low pass filter , thus generating a much sharper image to make CMOS sensors as sharp as their CCD counterparts , but if there is any resizing or manipulation these will still have to be sharpened . When shooting in RAW the sharpening will automatically be switched off .
When producing multiple images in different sizes for clients I will use my “TIFF” negative and create a sharpened version for each resized image , so that they always get the optimum quality . I use a simple naming system for these files using the product size (in inches) in the name
Customer order copies
This also acts as a reminder of which sizes the client orders to back up the order form , in case of any queries .
In this tutorial I have used GIMP , but the process and terms are the same in ALL image editing software packages.
We have now selected ,Processed , colour corrected and edited our image and we now want to print it for display either for customers or for exhibition or competition.
The final step of the process is to Sharpen the image using the unsharp mask option on our toolbox .Although our image will look sharp on the screen , if we have resized or edited it the edges will have interpolations within them that need to be aligned ,this is what the sharpening does.
From the tool bar select the filters section and from the sub menu “enhance” select unsharp mask
As you can see there are three parameters to the adjustment
Radius- the size of the area to be sharpened around the pixels affected
Amount – The actual amount of sharpening ,the higher the number the more sharpening applied
Threshold – The separation between colours affected , in an image with a range of tones this would be a lower number , in a high key brightly lit portrait against a white background this number would be higher as there is a larger spacing between the white background and the skin tones
As you can see the live adjustments box the effect as you sharpen the image , the settings for this image below being .
threshold 122 , this is because the racing car is white and the writing black .
This high key portrait will need a higher threshold number as the skin tones and white background are quite widely spaced on the colour spectrum with no mid tones. When sharpening portraits always use the eyes as a guide , as these will be the focus of the image .
As you can see , the settings for this image are
Radius 5.9 pixels
What happens if we over sharpen an image?,
As you can see the writing has developed distinctive halos and distortion around the edges , in colour images the tones in the image will change and give a much more noisy interpretation .
In Portrait Photography the image sharpening can have catastrophic effects if overdone , the image above is a Portrait which is unsharpened , so lets deliberately over sharpen it to see what happens.
This has been another amazing and in-depth article by Anthony Offen-James. A lifelong photographer and photography teacher, his knowledge and experience in photography is achieved by very few. Visit his site at http://www.anthonyoffen-james.co.uk/ and please leave any comments or questions in the section below!