Sally Jane Photographic Art

Fact Sheet 6

 

Pet Photography - The Value of Resolution and Pitfalls of Compression

Resolution and compression are two different things but both have an impact on file size. Many digital camera owners feel that they have to squeeze the most out of their memory cards by creating the smallest possible files every time they take a photo but this is a mistake as I will attempt to explain in this fact sheet.

Resolution

Resolution refers to the amount of pixels used in the image. It can be given in one of two ways; either by stating the pixel numbers for height and width (1280x960) or as a count of pixels in a square inch of image viewed at full size (72ppi - 72 pixels per inch). The latter is usually used as a display resolution setting while the former is usually how the camera's sensor resolution is described.

Do not confuse ppi with dpi (dots per inch) which is a measurement used by printers and bears no relation to ppi.

The maximum resolution a camera's sensor can handle will be defined by the MegaPixel rating of the camera. A 3 MegaPixel camera will allow you to take an image with a maximum resolution of 2048x1536 pixels while an 8 MegaPixel camera will allow a resolution of up to 3264x2448 pixels. The larger the MegaPixel rating the more pixels the camera's sensor has to record data. This is good because the more pixels there are in an image the more detailed the image will be. At this stage the term resolution and image size are one and the same thing. Most digital cameras will only give you the option to change image size as the ppi will be fixed. The ppi part of resolution only affects the display size of the image particularly when printing. The higher the ppi the smaller the image will print at 100%. For instance, an image with pixel measurements of 2048x1536 at 300ppi will produce a 7"x5" print but at 72ppi the print will fill an A4 sheet. Don't worry about this for now. I'll discuss ppi in a later fact sheet.

The difference resolution (or image size) makes when taking your pet portraits is that the images taken on a low resolution (small size setting) will show off the pets fur but images taken on a high resolution setting can show off the individual hairs! My advice therefore is always to use the highest resolution or image size available.

Compression

Most compact digital cameras will save the images as jpeg (or jpg) files. These are compressed files. A simplified explanation of this is instead of recording every bit of data from each of the individual pixels the processor in the camera bunches neighbouring pixels together that have a similar hue, saturation and lightness values and records them as one set of readings. This greatly reduces the amount of data recorded. How much depends of how similar the neighbouring pixels need to be in order to be classed as one. A high compression would allow for greater variation between the pixels and so less data recorded while a low compression would separate out the pixels more and so record more data. An image taken with a small amount of compression may appear perfectly OK and this is a good trade off for a reduced file size. An image taken with the high amount of compression will have a far smaller file size but chances are you will now see some degradation in the image. Not all cameras allow you to choose the compression applied but if yours does try experimenting by taking the same image on the highest and lowest compression settings and then view them on your PC screen or printed at full size. The highly compressed image will likely show patchy colour transitions and have a 'blocky' appearance (called jpeg artifacting) particularly along edges and outlines.

A few compact digital cameras will offer other file types, most common of these is TIFF. Unlike jpeg, TIFF files use a different type of compression that does not throw away data. Often the TIFF files that are created in a camera are uncompressed anyway. For this reason TIFF files are large and often slower to write to the memory card. If speed isn't important and you have this option, use it. Better still are RAW files but few compact digitals use these and to describe their use is beyond the scope of this fact sheet. If you do have RAW do take the time to research it and experiment with it; it truly is worth the effort.

My advice, just like with the resolution setting, is to use the least amount of compression your camera will allow. OK so this will greatly increase the file size and further limit the amount of images you can store on your memory card but the price of cards is falling drastically making memory these days is a cheap as chips. Better to have a few good images for your pet portrait than hundreds of useless one. You can do far more with a high resolution, minimally compressed image than you can with a small image that has had the life squeezed out of it.