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October 02, 2008
[ Blow-up! ]
Chez Imaging is a bit of a photographic museum, cluttered with cameras and lenses and doodads from the days of film.
The colour head enlarger, once the pride of the darkroom (now a store room and possum refuge) sits on the cupboard unused. We look at it from time to time and remember the toxic hours spent in the dark, making test strips to determine exposure and check sharpness. We don’t have to do that any more.
A visitor spotted the enlarger the other day and asked: “How do you enlarge a digital image?” He hadn’t thought of it before. But when domestic printers routinely handle up to A3+ paper (329X483mm) it is a reasonable question. After all, a 12 megapixel camera image at 300dpi (probably higher resolution than the printer requires, but that is another matter) measures 241X363mm. And if the image is cropped then the degree of enlargement increases. So, how best to do it?
Simply resizing the image in Photoshop or Paintshop Pro in a single hit will not do the job. Crude enlargement softens the image and, in extreme cases, causes pixelation.
There are commercial applications that handle digital image enlargement, the best known of which is Genuine Fractals, for both Win and Mac. (http://tinyurl.com/4vp2tl) This does an excellent job but it is expensive at USD160.
Fred Miranda claims that his Stair Interpolation Photoshop plug-in makes a better enlargement and costs a more realistic USD25. (Win and Mac www.fredmirands.com/shopping/ ) We have used Fred’s plug-in (at first it was an Action) and been well satisfied.
Miranda’s approach is to start with a well-known characteristic of digital enlargement and to automate it. In its most basic form anyone can do it, so there might not be any need to spend money at all.
When a digital image is enlarged in ten per cent increments the tendency to blur and soften is hardly discernible, even up to extreme degrees of enlargement. The technique described here applies to Photoshop, but it can be adapted for Elements or for Paintshop Pro.
Starting with the open image go to Image/Image Size and change the Document Size line to Percent. Then type 110 into the Width box, the height will auto adjust. Make sure that Scale Styles/Constrain Proportions and Resample Image are all checked.
Next change the Resample Image method to Bicubic Smoother and press OK. The image is now increased in size by ten per cent. Because it would be tedious to go on doing this over and over (although in Elements there’s not much choice) the steps should be recorded as an Action and assigned to a function key. The Action then sits in the Actions palette and is simply run over and over with a repeated single key stroke until the degree of enlargement required is reached. Easy and cheap and very effective.
It is important not to sharpen the image until the enlargement process is complete. The difference between enlarging and reducing image size in Photoshop is that for reduction the resampling method is Bicubic Sharper (“best for reductions” says Adobe) and for enlargement is Bicubic Smoother (“best for enlargements”). Then, once the enlargement is complete, a discreet application of Unsharp mask may finish it off nicely.
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Posted by terry at October 2, 2008 12:25 AM
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Comments
G'Day Terry,
Sorry to read that you've effectively retired your colour enlarger, they are still capable of producing superb photos, particularly Black and White and Cibachrome colour. As far a digital enlargements are concerned, Adobe Photoshop handles these reasonably well if when you resize an image select; Resample Image: Bicubic Sharper. This will increase the file size of the image from around 6MBs to nearly 2GBs. This can take a very long time if you do not have sufficient RAM in your computer.
I print my photos on an Epson StylusPro 9600 printer and have printed RAW images taken with my Sony DSC-R1 and Canon EOS 5D up to the 44 inch/111.8mm X 60 inch/1500mm which are very sharp and clear.
Regards,
Bob
Posted by: Bob at October 2, 2008 06:12 AM
Hi Terry,
I have been soaking up articles like this one and podcasts about digital post production but i wonder if you could advise about courses available in Melbourne for more in depth skill development. For example courses offered by TAFE, private providers etc. I would be looking for more than CAE hobby style programs.
Marg
Posted by: Anonymous at October 7, 2008 08:47 PM
Marg: If you are looking for a fully professional photographic course you might start by inquiring about the RMIT offering. Swinburne also have a photography course. TL
Posted by: Terry at October 7, 2008 10:51 PM