Digital Photographic Images - Part 3: Resizing and Optimizing Images
By Robin Henry
With the price of cameras and other digital image capturing devices dropping, everyone can now produce dozens of digital images easily and inexpensively. While anyone can produce a digital image, it takes additional knowledge to manipulate the images. This article discusses several of the options available to prepare images for transmission via email or for posting on the Internet.
The Nature Of Digital Images
Digital images consist of picture elements (pixels for short). The total pixel density of an image is calculated by multiplying the horizontal row of pixels by the vertical column of pixels eg, 640 horizontal by 480 vertical (the size of some computer monitor displays) which equals 307,200 pixels.
Digital images displayed on visual display media generally use a rate of 72 pixels per inch (2.5 cm), but this resolution (the number of pixels per inch) is unsuitable for hardcopy printing without degrading the appearance of an image. Thus, anything produced for hardcopy printing needs to be of much higher resolution. And here lies the heart of some of our challenges.
Digital cameras come with a range of resolution settings. For example, my Panasonic Lumix has a top setting of 6 million pixels (2816 pixels horizontal by 2112 pixels vertical) and a lower quality setting of 0.3 million pixels (640 by 480). As would be expected, a larger number of pixels takes up more space than a smaller number of pixels.
I use the analogy of a book: you have a book with a beautiful cover, but underneath the cover you have numerous pages. A large image is represented by a very thick book ... a small image by a thin book. (This is not exactly correct, but is suitable for our discussion).
When you use digital images for hardcopy printing, you need a thick book. When you wish to email them or place them on the Internet, you need a thin book. Let's see how we can make the change.
Rule of Thumb
Create your images at a higher resolution than you need and reduce the size to suit. While high resolution images can be reduced and retain quality, it's not possible to improve the quality of a low resolution image by increasing the resolution.
Resizing Images
There are many utility programs available that allow you to resize images. Usually they require you to enter the number of horizontal and vertical pixels you wish to downsize to or alternatively, you can simply 'grab' a corner of the image and stretch it up or down. When you resize, you need to be aware of the aspect ratio (the ratio of the horizontal pixels to the vertical pixels eg, a television or computer monitor screen is often 4:3). If you don't maintain the ratio you'll find that your image is distorted. Typically an image of people will make them look unusually wide and short or tall and thin when aspect ratio is not maintained.
The easiest way to maintain aspect ratio is by grabbing one of the corners of an image and dragging it towards the center. That way, the resizing is symmetrical.
Cropping Images
Cropping occurs when you take a piece out of an image. Utility programs that allow cropping usually have a lasoo (a tool that allows you to create a square or rectangle on your image) to outline the area you wish to crop. When you crop, all of the image outside the defined rectangle or square is disposed of, thus reducing the number of pixels and weight of the image (think of a book as having pages torn out and the weight reduced). Cropping is particularly useful to get rid of the parts of an image that don't make any significant contribution to the aesthetics of the image eg, additional, wide landscape.
Optimizing Images for Email or Internet Use
If you cropped and resized a 6 million pixel image by half you've now got a three million pixel image. The next step is to use an optimization program to optimize it for the Internet or email. Optimization processes generally extract pixels that aren't necessary for the image to display. For example, the image may contain 10 different shades of brown, nine of which can be discarded without making a significant change in quality of the image. So, the utility reduces the number of pixels by getting rid of the surplus brown pixels. These changes are usually done in low, medium or high quality and you can choose the degree of change before comitting to the optimization.
Once your images are optimized they take up less disk space and are therefore easier to email and more suited for Internet use.
Learning More
The short exposure in this article won't make you an expert, but should at least have familiarized you with the processes of resizing, cropping and optimizing. Look on the Internet under relevant headings for further explanation and get yourself a good utility program that will allow you to manipulate your digital images.
Copyright 2006 Robin Henry
Robin Henry is an educator, human resources specialist and Internet entrepreneur. He helps home-based businesses and individuals improve performance by applying smart technology and processes and developing personally.