Digital Photography Class 9

The last of our classroom based class of this term, and indeed the year. Tonight we were looking at resizing images, and the reasons why we might do this.


The size of images we take with our digital cameras are measured in pixels.  So what are pixels? In digital imaging, a pixel, or pel, (picture element) is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled.


Each pixel has its own address. The address of a pixel corresponds to its coordinates. Pixels are normally arranged in a two-dimensional grid, and are often represented using dots or squares. Each pixel is a sample of an original image; more samples typically provide more accurate representations of the original. The intensity of each pixel is variable. In color image systems, a color is typically represented by three or four component intensities such as red, green, and blue, or cyan, magenta, yellow, and black.

This example shows an image with a portion greatly enlarged, in which the individual pixels are rendered as little squares and can easily be seen.

In some contexts (such as descriptions of camera sensors), the term pixel is used to refer to a single scalar element of a multi-component representation (more precisely called a photosite in the camera sensor context, although the neologism sensel is sometimes used to describe the elements of a digital camera's sensor), while in others the term may refer to the entire set of such component intensities for a spatial position. In color systems that use chroma subsampling, the multi-component concept of a pixel can become difficult to apply, since the intensity measures for the different color components correspond to different spatial areas in a such a representation.


The word pixel is based on a contraction of pix ("pictures") and el (for "element"); similar formations with el  for "element" include the words voxel and texel.


Most pictures that come out of our cameras these days are quite big, and some are about 5mb in size, some may even be bigger. The main reason to resize some of our pictures is for the purpose of emailing them. Quite a lot of us have relatively fast broadband Internet connections, but it is something we shouldnt take for granted, as other may not have. What might take our computers a couple of seconds, might take a computer on a slower Internet connection several minutes to download. So we should really consider shrinking the size of photographs the next time we are going to send a dozen or so images to a friend attached to an email.

For step by step instructions on how to do this in all versions of PaintShop Pro, refer to the notes I gave in previous classes, they can be downloaded by clicking this link.


Next week for our final class, we will be wrapping up warm, and going on a Yuletide outing to take some photographs of the Cardiff Winterwonderland. 


A reminder to those in the group, we are meeting on the steps of Cardiff Museum at 7pm on Tuesday. If the weather is terrible, then we will abandon this, and go to the school instead. I will post on this blog at 6pm Tuesday with a live update as to whether or not we are still going. The students from the group have my mobile number, but those of you who missed class and wish to join us, can email me for my number. 


See you next week!  Ho ho ho!