by Tom Lee Published 01/11/2006
Resolution for Printing
The major source of confusion here is the difference between pixels per inch and dots per inch. To be accurate, dpi is a printing term and when Epson says that their printer operates at 1,440dpi you do NOT need a resolution of 1,440ppi in your image. Each pixel in the image is built from around 12 drops of ink, two from each of six colours. In practice this means that you divide 1,440 by 12 to give you a working image resolution of 120ppi.
Then, in order to allowfor the variable dot technology™ and its ilk, Epson actually asks you for a resolution of 180ppi in the sized image. The last four words are vital to understand. Every inch run in the image needs180 pixels, so a 10-inch image needs 10x180 = 1,800 pixels. So for a Nikon D200, with a pixel count of 3,872 by 2,592 you can print an image that is 21.5inches by 14.5inches without the need for Photoshop to create additional pixels by interpolation (3,872/180 = 21.5).
In practice you can double thesize and get away with it most of the time, so a 40-inch print will still look OK. Conversely, if you scan a 35mm transparency at 3,000ppi, your image might transfer to Photoshop as 1x1.5 inches, but at 200ppi it will still make you a 15-inch print (3,000/200 = 15 inches). To make such a 15-inch print you either have to go to Image Size and change it or, more conveniently, let the printer driver do the job - when you ask Photoshop 'Print with Preview' to 'size to fit'. Providing there are sufficient pixels, there is no need to check the Resize Image box which makes pixels (by interpolation) and increases the file size or deletes pixels and reduces it.
Reducing the pixel count (ie file size) is important for web use so that images are displayed accurately and small enough for rapid loading. Make them too large and they will take ages to load and often over-fill the screen so that the entire image is not visible. Even if your program makes the images fit to the screen (such as PicturesToExe - see later), it is still often better to take charge of the size optimisation process yourself, especially if sharpening is involved.
Bear in mind that printers other than inkjet may require different resolutions. Check with your lab before you finalise your workflow. By way of example the Fuji Frontier needs 300ppi, the Fuji Pictography 267ppi and process printing (eg this magazine) needs 300ppi. Newspapers need less resolution and experience will teach you that inkjets made onto rough or art surfaces such as canvas will actually need less resolution. All the usual rules of photography actually apply here, a good crisp original will almost always blow up bigger than a poor,
Making Slide Shows
The requirements for a professional photographer making 'slide shows' are different from the public at large. There is a need for top-quality presentations that will run on computers and televisions using CDs, DVDs or self-executing files to run on monitors via a PC or sometimes a Macintosh. The output might be delivered onto a monitor, TV, HDTV or a digital data projector. In addition there may be some requirement to create media that cannot be fraudulently copied and you may have to include text so that your client may order prints. As if this was not enough, you also may wish to have music and fancy slide transitions to enhance the viewing experience.
Faced with a wish list like this, it is a daunting task to decide how to go about it. Even when you have a workflow sussed out, you have to ensure that it is robust to all the possible playback options. DVDs are currently at the stage that CDs were some years ago. They may or may not play on a specific machine. Today the quality DVD mastering company will test your product on as many as 20 machines. The best discs only play on about 90 to 95 per cent of players so you should not be surprised if your 'home-made' DVD fails to run on your client's player. A starting piece of advice is to always use top (A) grade blank discs.
Those made by Apple, Fuji, Maxell, Sony, Taiyo Yuden, and TDK are regarded as OK, treat all other brands (including some big names!) with suspicion (see www.newcyberian.com). At all costs avoid unbranded products - even if you do manage to write them they may not last. Writing at slower speeds is also helpful, the maximum speed of which your writer is capable will, in many cases, produce a less reliable product.
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