How do you make the volume of the plastic bag smaller? You can either throw stuff away, or you can make the bag fit better around its contents (by sucking the air out for example). When you want to make a file smaller you can compress it in one of two ways, to visualize this you can imagine placing a object into a plastic bag. The process of making a file smaller is referred to "as compressing the file". Some formats reduce the size of the file dramatically, this can aid the delivery of images over the internet where file size is a factor in determining how fast an image loads in a browser. It is good to know a little about image formats so you can know which is the best format for your purpose.įile size is an important function of a format. The most used formats are TIFF, PNG, GIF, and JPEG. Each of these formats has its strengths and weaknesses depending on the purpose. If you saved the picture as a GIF then the rules describing the picture of the house conform to the GIF format. This means that the image file describes the image of the house using the rules of the JPEG format. You may decide to use the method for describing the picture known as JPEG - so you save the picture as a JPEG. For example, a digital picture of a house can be described in many ways. The way you describe how these components work together is known as the format. There are many methods for describing how the pixels and columns and rows make up an image. A pixel is the smallest unit that makes up an image. Each unit of these columns and rows is known as a pixel (short for picture element). This file describes columns and rows which make up the image. Paintshop, GIMP, Adobe Photoshop) or other devices and software.Ī Digital Image File is a file that contains the information that describes the image.
GIMP COMPRESSION LEVEL SOFTWARE
Digital images are produced by scanners, digital cameras, image software (eg.
Better to leave it off. Space savings are minimal, and files take longer to decode.You will most likely be familiar with digital images through webpages or the pictures on your computer. Optimize. This just optimizes some compression internals. Doesn't hurt to enable. Space savings are moderate.Subsampling. Digital cameras usually use "4:2:2 horizontal (chroma halved)". Pick the option that halves the longer dimension.Arithmetic coding. Don't enable this setting. Such files will not work with most image viewers or web browsers.Quality. Digital cameras usually use a setting similar to 94-98.When exporting to JPEG, there are several settings that affect file size. The primary settings to consider are in bold. For details, see What factors cause or prevent "generational loss" when JPEGs are recompressed multiple times?.To maximize efficiency (lost data vs change in file size) when resaving JPEGs, it's usually preferable to use settings that are as close to the original as possible. GIMP has an option to facilitate this: Use quality settings from original image. A difference between the settings used by GIMP and your digital camera likely explains the change in file sizes you're seeing. By default, GIMP appears to export JPEGs with quality 97 without subsampling. Many older digital cameras may use quality settings around 80-90 with subsampling. Using the first photo I encountered on my computer, saving with Q=90 + 4:2:2 subsampling resulted in a 3.9MB file. But saving with Q=97 + 4:4:4 subsampling resulted in a 14.1MB file. The change in file size is about 3.6x.
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