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Begin an adventure with a digital camera.

4. Compression, size, resolution

2006-12-10

A lot of beginners using the digital camera want to save on their memory card as much photos as it is possible. They try to achieve it by the smaller file size and by the increase of the jpg file compression.

Obviously, these solutions are available in any camera and I can't tell they are inefficient. However, it should be followed by the awareness of its consequences. We should know what we want to do with the photo just before we change the file size and sort of data compression.

The number of saved photos on the card always will depends on:

• capacity of the memory card (128MB, 256MB, 512MB, 1024MB…),
• file type (JPEG, TIFF, RAW),,
• photo size (1MB, 2MB, 3MB, 4MB, 5MB…),
• size of data compression (small, average, big).

We should read a manual instruction to learn exactly about the abilities of our camera in the mentioned issue. Every camera type can have different file formats, different sizes of photo we can choose and levels of photo compression.

What is a photo size?
The photo size is a number of pixels that the photo consist of. As the greater number of the pixels the file (photo) is larger and the more information about image. In case of the camera with 8 MB image sensor we achieve the photo contained so much pixels. Every pixel can be specified with one of 16 million colours. All of the pixels made the image which we call the photo. The size have an influence on the side length. Currently the image sensors are in the ratio of 4 to 3 or 3 to 2. The developed photo also will be in this relation. In case of the mentioned photo of 8 megapixels and the sides ratio of 3:2 we will receive the file with the sides of 3456x2304 what gives us 8 megapixels (approximately). The image size is different thing then photo resolution but these terms are used interchangeably in the every day language. The decreased photo size decrease also its weight what means the greater number of the photos saved on the card.

What is a photo resolution?
The photo resolution is the quantity of the pixels in the one inch. It's the linear value what means it's measured in a straight line. Because the pixels are the points of the same size their number in the one inch is constant. The photo from the digital camera saved in the JPG format is usually 72 pixels per inch (ppi). Such pictures are accurate to the monitor. To the prints the greater resolutions are used.

What is a difference between the image size and data compression?
The image size effects on the sides length. With the lower size there is less pixels photo consists of, what means the width and height also will change.
The compression doesn't effect on the image size. With the greater compression neither the height nor width will change - the number of pixels will be the same as before the compression. However, the compression effects on the photo weight i.e. the capacity of card it take. The compression is available with the JPEG file format and it seems some information about the image will be lost. The photo quality and weight will be changed.

In order to choose the image size and the data compression we should know before the photographing what we do with the photo later!

If we want to show our photos in the Internet there's no need to take the photos we the large sizes and low compression. The accurate size is 640x480 or 800x600 and average compression.
However, such photo size won't be enough to develop it in the laboratory. There the size will depends on the size of print we want to obtain. For the sizes 10x15 2 megapixels will be enough (1728x1152). More specific information about the available photo sizes are in the manual instruction.

Personally I take the pictures with the highest size is available and with the lowest compression. What I obtain is the big sizes of the photos which need a lot of space in the memory card and in the computer. In exchange I get the highest number of details and high photo quality. What's more I can frame the photos on the computer and even the ability to return to selected photo and do e.g. the A4 print. In case of the big file the photo processing is available, which always effects on the loss of details. It's worthy to have a reserve. Because I never know which photo I will want to process with the graphic program taking of big photo give me better opportunities in the future.

Have you already know how to enlarge the number of written photo on your memory card?

It doesn't matter which solution we choose. It's worthy to have the awareness of the consequences of our choice.
I choose the bigger card size and more often transferring of photos to the computer and further to the DVD. What you choose depends only on you.