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"La fotografía es controlar lo que está delante de usted y lo que hace su voluntad."
Arnold Newman
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SOLVE YOUR DOUBTS
One of the issues of digital photography has further confusion is the size and resolution of images.
Any digital image is from a camera or scanned film is formed by a given number of pixels. A pixel is the smallest unit that makes up a digital image and we can imagine it as a tiny dot of one color among millions of possible colors or a particular shade of gray in a black and white image.
Due to the limitations of our vision, when these pixels are small enough, we can not see them as individual points, but as a whole, feigning a continuous tone image. This is not new. We have been seeing in magazines that printed images look perfect multicolor images when they are actually made of tiny ink droplets only 4 colors: Yellow, Magenta, Cyan and Black.
Returning to our pixels, we have an image formed by a number of them distributed in a two dimensional array of 'X' pixels high by 'Y' pixels wide, resulting in an image of 'XY' pixel. Consider the image on the left.
We opened in Photoshop an image of a Canon EOS 10D, 6 megapixel selected 'Image / Image Size. "The table 'Dimensions seeing is composed of 2048 pixels wide by 3072 pixels wide, this is more than 6 million pixels per market Red, Green and Blue, 18 million in total.
So far everything is quite clear and open to little confusion. We have a set of digital values in a file stored on a hard drive or memory card comprising an image. But to enjoy that image we have to transform it into something physical that our eyes can interpret. To do this we will use some kind of ingenuity that we call 'output device' and will usually be a computer screen or printer.
To fulfill its mission, the output device will read each of the values for each pixel of the digital file and distribute evenly over a surface, either the screen of a monitor, either a sheet of paper, of a certain size. The distance between each of these pixels in the hardware that contains what is known as resolution.
Resolution is measured in pixels / unit length being the standard unit of length inch (25.4 mm) by that which the inventor gets the name. We can see that the resolution is closely related to the output device and that will determine the size that will occupy space in our digital image.
In the picture above, I have deliberately chosen 72 pixels / inch as the value for the resolution. This is a normal value for any computer monitor. We see that in this case, our image has a size of about 105x72cm. Surely our minitor not be that big, so if we visualize the image at 100% size, we can only see a small part of it.
The resolution of a monitor, 72 pixels / inch, is a relatively small, so that our image easily reach a large size so large that we reduce it to fit comfortably in our screen and that it can be seen in its entirety as in if you want to show our picture on the Internet.
With the printers something quite different happens. As I said above, so that an image formed by pixels appear continuous tone, these pixels should be small enough to fool our eyes and this involves putting on paper at least 200 pixels / per inch of paper. Most printers, however, use higher resolutions, typically 300 to 360 pixels / inch. With these resolutions, the pixels are so close together that the size of our image will take on the role will be drastically reduced.
Writing the appropriate output resolution to your printer, 360 pixels / inch in this case (with the Resample Image box off) we see that our image, which previously was over a meter tall, now barely reaches the 15x22 cm.
If your camera can not capture a sufficient number of pixels to obtain an extension as large as you wanted. Do not worry, the solution is simple and is called interpolation. Interpolation is a mathematical function whose result will generate new pixel values by taking as input the values of adjacent pixels.
That is, interpolation inventing new pixels based on around you. Of course, the interpolation will not get you more image details, but if you have more pixels and these are small enough so that your image printed on paper appears to continuous tone, no matter how large the eventual size of your photography.
Again, thanks to the limits of our vision and imposed by the depth of field, you can create copies of oversized look great from digital files smaller than one might initially think. Using our calculator, you can get an estimate of the maximum possible size for your copy, depending on the resolution of your camera and viewing distance.
To enable interpolation in Photoshop, just have to check the 'Resample Image' and enter the new data width or height desired. The rest is a completely automated process that requires no further intervention on your part.
Suppose you decided to order an extension of 40x60 centimeters from your image of 6 megapixels. As we print at 360 dpi (ppi = pixels per inch), you have to write this value in the Resolution. Activate the box Resample Image and Constrain Proportions, thus writing only one of the desired values of height or width, the other is calculated automatically. Suitable interpolation algorithm to enlarge the size of an image is Bicubic Smoother or, if unavailable, only Bicubic.
Notice also increased the number of pixels in your image going from 3072x2048 pixels to 8504x5669 which makes a total of nearly 140 million pixels, a value much higher than the best digital cameras today.
Now, nearly 120 million pixels are fabricated and provide no real information in your image. This may seem too much, but do not worry. Seen from sufficient distance (1.5 times the diagonal about) your image will look perfectly clear. If you get closer you will notice that the details are blurred but your image still looks continuous tone, the pixels are not.
Now, only apply to your image, the Unsharp Mask filter, and keep a copy in JPG quality 10. This is the file that you send us so we can print your copy in the rigid formats that you have at your disposal.
If the size of your paper copy is larger than 40x60 cm. You can optionally use a value of 180ppp instead of 360 dpi.