With all the digital cameras out there now it is surprising how few people really understand how the things work and what the terms mean. So here it is.. don't worry, it really is easy.

A digital photo is composed of an orderly grid of small dots of various colours organised to form an image. The resolution is generally refereed to as DPI, which means dots per inch. If you have a photo that is 20 "DPI" that means there are 20 little dots across the top and 20 along the side. so you have 20 rows of 20 dots as you see in the graphic below. That means there is 400 "bytes" of information in every square inch of a photo with this resolution. As most photos have many more "dots per inch" than this you can see why photos are large pieces of data.

So a photo that has a dimension of 4X6 inches and 20 DPI is 4X6=24X400=9,600 bytes or expressed another way, 9.6 kilobytes or kb. Kilo meaning 1000.

But lets say you have a photo that is 10X8 inches and 300 DPI. That makes a "file size" of 7,200,000 bytes of information or 7.2 megabyte or just "meg". Mega means million. Thats a very large file of information. This is refereed to as a "raw" file. You may have seen this as an option on your camera but didn't know what it meant except if you used it your camera got real slow and it made a file that you may not have been able to open. Because this would be too hard to store and transmit, programs were developed that would "compress" files. JPG is the most popular of the compression programs. What it does is examine your "raw" file and finds adjoining dots that have the same or similar colour value and instead of counting them separately it lumps them together to form one piece of data. This is an adjustable system. Your windows photo email system increases the compression as well as decreasing the DPI and dimension. This makes for a small file but it can also create a distorted look to the image. Below is a pic that has had a very high compression applied to it. It should illustrate the idea well though.

 As you can see, excessive compression can be destructive. Normal JPG settings make a smaller file without detectable result, at least not detectable unless magnified a lot.

Photo files can be massaged into various configurations. The constant is "FILE SIZE". In a production program, you can increase or decrease the dimension easily but the file size will remain the same because the image automatically changes the DPI as you do it. So if I enlarge the size on my screen the DPI reduces as I do it. Conversely, if I decrease the size on my screen the DPI increases. The total file size remains the same unless I 'resample' the image, meaning in effect, taking a picture of the existing picture.

I can pick a dimension and bring down the DPI with a program but once any data is discarded, that's it, it is gone for good. If you instruct a program to increase file size by adding DPI to an image of constant dimension, all you are doing is taking a high resolution photo of a low resolution image. You get a bigger "file size" but the same old shitty image.

When TCP asks for photos we don't specify DPI because it means nothing unless you specify dimension as well. We make it easy and just specify File Size. That is the constant. To find out about the file size of photos in your folders, simply move your cursor over the image and wait a second and a window will pop up that tells you the pixel dimension, how many pixels total for width and height, model of camera, date taken etc... as below.