Microstock Image File Definitions

Selling photographs through Internet based Microstock Agencies is a good way to make money as a sideline to your photography. But if you are more interested in taking pictures than using a computer, some of their terminology can be a little confusing for the new submitter.

All Microstock Agencies have rules defining the :

• images sizes (upper and lower limits)
• file formats
• file sizes (usually just upper limits)
  

Lets try and define what they mean.

Most Agencies now set the lowest acceptable image size as 4 Megapixels.

When an agency says 4 Megapixels they mean that total area of the image must be comprised of at least 4,000,000 pixels ( a pixel being one of the coloured dots that make up the image).

I should just say that Mega does not always mean 1,000,000.
In strict computer speak it should mean 1,024 x 1,024 i.e 1,048,576, but the various technology industries tend to use it to mean any number around a million and then don't mention that there might be some overhead due to software variations.
So if your camera says it is creates a 10.2 Megapixel image but actually creates a 10,036,244 pixel image, don't be surprised.

A typical digital camera has an aspect ratio of 3:2 (width vs height)

So if your camera is rated at 6 Megapixels you will get images 3 Mp wide x 2 Mp high

Width x Height = Area

Hence the image is 6 Megapixels in size

A digital photograph is always stored on your camera or on your computer in some sort of encoded file, which will contain information on colour and the way individual pixels should be interpreted.

File size is expressed in Megabytes.

Although Megapixels and Megabytes might sound alike they are not the same; their relationship depends of the compression type and encoding of the file format.

The Agencies usually insist that you submit your images in the JPEG format (the file will have a .jpg extension).
Most cameras will store their images in JPEG or RAW format, if you already use RAW format you almost certainly don't need to be reading this. Stick with JPEG to start off with.

JPEG is a compressed format; this means that it can magically (actually mathematically, but that is often the same thing) reduce a 42Mb file to 3Mb.

JPEG is also a potentially 'lossy' format. This horrible word means that you can compress the file even more by reducing its overall quality. Avoid this, always store JPEGS for microstock at maximum quality.

The lossy nature of JPEG's mean that every time a file is saved in this format more data is lost. Try to keep the number of editing session on one image to a minimum and always keep the original unchanged so you can go back and start again.