BMP, TIFF, JPEG

BMP

BMP is the file extension for the bitmap file format created by Windows to store images. Bitmap images are made up of pixels (aka dots or bits) of colour on a type of grid. Bitmap is “resoultion dependant” which means that the screen displaying the images must have the correct resulotion to show images, e.g 32 ppi (pixels per inch). Bitmap started off for early computers and only had 1-bit of colour. Meaning it could only show black and white. It soon evolved into 2-bit meaning it could show up to four colours and then 8-bit which could show 256 colours. This is known as the ‘bit depth’. The larger the bit depth, the more colours allowed in an image. However, having more colours can be a disadvantage because with a greater bit depth comes an increases download time and file size.

TIFF

TIFF stands for Tagged Image File Format, file extension is .tif. It was created jointly by Microsoft and Aldus as another, more effective way of storing images up to 48-bit. TIFF is supported by all operating systems and is the most widely used file format for storing images both commercially and professionally. It supports different colour modes such as RGB, CMYK and Greyscale for a more effective and flexible use. Unlike other file formats such as BMP and JPEG, TIFF does not compress the files and so no quality is lost. This is important for making master copies and archiving because you always get back exactly what you saved. It is commonly supported my image editing applications such as Photoshop. the ‘tagged’ part of TIFF is a set of important information that says what colour mode it is, what the dimensions are and other improtant specifications. TIFF has a big disadvantage compared to other image file formats. A larger image file can take up anywhere from 5 times more memory than a file format such as JPEG which means that a lot less images can be saved.

On the left is a TIFF image when it is reopened, on the right is a JPEG. We can see the different quality. The TIFF has not become partially pixelated because of the compression.

JPEG

JPEG stands for Joint Photographic Experts Group and is a way of storing bitmap images. it’s file extension is .jpg. These images are known as ‘lossy compression’ techniques because they compress images and cause them to loose some of their original quality. If the siza of the image is decreased, it could be used as a thumbnail but in a lot less quality. if it is saved over the original image the quality cannot be restored unless it is recreated or rescanned. This is a major flaw with the JPEG file format. In the same way as bitmap, JPEG images are made up of individual pixels which can be seen if you zoom in on the image.

JPEG images are 24-bit and have the nickname “True Colour” images because the display more colours than bitmap images. People from photographers to graphic designers find JPEG more useful then bitmap and overtime has relaced it. a new JPEG format called “pregressive JPEG” gives images better quality but this also increases the file size. although this is a disadvantage, the file is given a pewview so the user can see what the image is without waiting for the file to download.

~ by Fizwidget on October 1, 2007.