Digital imaging basics - From pixel to paper

Perfect printing

Nowadays it couldn't be easier to feel a 'real' photo in your hand. Producing real digital photos is quicker than with analogue photography. A product like the Epson PictureMate PM280 photo printer is a welcome guest at any party. You can take pictures with your digital camera and this portable printer can produce photos almost immediately without needing a computer. It is enough just to insert the storage card, select the photos, and then press the "Print" button. You can also print directly from CD, form digital camera's or even from mobile phones using the bluetooth option.

Depending on your experience and equipment, you can print photos with Epson products which are good enough for any gallery. And you don't have to attend in depth printer training, either. But you should be familiar with the most important facts to get the best from your photos.

The larger part of the work is already done by Epson technology: both the camera and the printer agree on the result when both use "Print Image Matching III".

As soon as it's taken, the picture is optimized so that it will look its best on both monitor and printer. The printer not only knows whether the exposure is a portrait or a landscape, it also takes into account more than 20 different parameters like contrast, image sharpness, brightness, saturation, and colour balance.

But even here, the colour palette can slip if the printer software is not set up for the output device and the photo paper. After all, the pictures are going to a device which has to follow the rules of its own construction. So it may mix its palette from the colours of cyan, magenta, yellow, and black (CMYK), while the camera and monitor work with red, green, and blue (RGB). In order to produce the same colours with these different tools, careful colour management is essential.

With new tools like Epson PhotoEnhance you can automate this complete process.

The right resolution

The best technology can't help if the raw material, the pixels, are missing. All details of the image are made up of pixels, like tiny mosaic stones. The more of them you have, the more finely the patterns and colours are resolved. If you are using the Epson R-D1s you will have plenty of them. Even at the lowest setting, prints of 20 centimeters in width will succeed without being able to see a single pixel. If you are using a different digital camera check what resolution it offers.

However, you shouldn't be fooled if pictures look a lot larger on the monitor than on photo paper. The reason for this is that the monitor only needs about 96 pixels per inch (2.54 centimeters) to display a picture comfortably for the eye. On paper, you need a lot more pixels packed into each inch.

An inkjet printer, for example, should be able to print about 300 pixels per inch to create smooth gradients. It must place its primary colours closely next to or on top of one another in order to simulate a mixed colour for the eye. A purple dot, for instance, when examined more closely, consists of a collection of pixels in magenta and cyan, which are packed together in a so-called raster cell. The number of cells determines the actual resolution of the print. At medium photo quality, Epson photo printers print about 180 such raster cells per inch (lpi), but the most outstanding results are created using 360 lpi.

Calculate printer output

The computer can tell you the minimum requirements for a picture for it to be printable. For example, enter the desired dimensions of your photograph in centimetres, say, 9 by 13. The fields below will tell you, among other things, the length and height in pixels which is required. Use a period for the decimal point. The resolution or raster width of the printing process should be entered in the "Resolution" field. Important: for the calculation to work, JavaScript must be enabled in your browser.

Lines per inch (lpi)

LPI resolution shouldn't be confused with dpi - e.g. 720 dpi, 1440 dpi, or higher values, which usually appear in user manuals. Instead, the so-called raster width is intended, which is given in lines per inch (lpi). Printers place some primary colours so close or on top of one another that the eye sees a mixed colour. A pink dot, therefore, when examined more closely, consists of a collection of dots in magenta and yellow, which are clustered in a so-called raster cell. The number of cells is given in the unit lpi. Depending on the printing process, this may be between 60 and 300 lpi. At 200 lpi, you will usually be fine with photo printing. After clicking on "Calculate", you will see the dimensions in pixels, the total number of pixels, and the file size.

Printed size desired
Paper height		Paper width	Unit	Resolution (lpi)
	x		cm inches	180 medium quality 270 good quality 360 best quality
Image size:		pixels	x	pixels
		Total pixels		File size, MB

Print output

Do you want to know how large an existing picture will appear when printed? Then enter the length and width of the picture in pixels. Under "Resolution", enter the standard values for the printer.

Pixels present:
Pixels, vertical		Pixels, horizontal		Resolution (lpi)
	x			180 medium quality270 good quality360 best quality
Printing size:		cm inches	x	centimeters inches
		Total pixels		File size, MB