Resolution, File Size and File Formats

One of the less glamorous topics we'll cover but necessary to understand.

File Formats:

jpg = great for photographs, allows for compression
gif = great for graphics and animations, allows optimized palettes
png = Used for online but less than previously, allows for compression
bmp = format started by Microsoft, used on their machines

RESOLUTION:

72 dpi for computer and television screens
150 dpi for newsprint
300 + dpi for printing on coated glossy paper

Usually the larger the file size, the larger the pixel dimensions.

Two jpgs both with 72 dpi and same quality of compression but with a different pixel dimension ... The larger one will have a bigger file size.

Two jpgs both 72 dpi with the SAME pixel dimension but a different file size...one is more compressed with a lower quality than the larger sized file.

You can easily make a high dpi (300) image smaller in resolution by changing the dpi to 72 if it will be on the internet. The image size can remain the same or made larger. The extra dpi can be exchanged to a larger dimension.

However an image with 72 dpi cannot be made to be 300 dpi unless you reduce the final document size by changing back the pixel dimensions to what they had been prior to stretching it from 72 to 300 dpi.

WHY IS RESOLUTION IMPORTANT?

For images to be clear when you print them, they have to have a high enough dpi. Stretching images are a bad idea because it causes pixelization and blurring. This is very important to avoid for items to be printed.

For images to be small enough to download quickly in a browser, they need to be compressed in a file format compatible with browsers.

QUALITY OF IMAGE AND FILE SIZE ARE LINKED TOGETHER.
When one rises so does the other.

RESOLUTION (DPI) and SIZE ARE LIKE A TEETER TOTTER...A huge image can be shrunk down to be 300 dpi and still not lose any quality. A small image can be stretched larger as long as a high dpi is exchanged to a low dpi.