Image Resizing is a topic most newcomers to digital imaging struggle with. First of all, why resize an image? The main reasons are to do with what you are going to do with your images. Raw images from your camera are going to be large in file size and generally large in physical (print) dimensions. If you want to email them they need to be small files, if you want to print them out postcard size, you are going to need to reduce their physical size - but retain maximum quality.
First of all, open the original 'bear.jpg' image, and rotate it as we did in Task 1.
Resizing images in Paint.net is relatively easy but the concept takes a little getting used too.
Open the Resize dialogue by going to the Image menu and choosing Resize.
You will then see the dialogue box on the left. Take a moment to study it.
Note the Pixel Size section. This is an original camera image. How many pixels Width is it? What is the Resolution?
Note too the 'Print Size' section. This gives
you the physical dimensions of the image.
Every digital image is a 'grid' of pixels. The number of pixels and the resolution in 'pixels per inch' determines the physical (print) size of the picture.
The bear image is from a 2 million pixel camera. Arrowed is the uncompressed file size of the raw image (5.49Mb).
Below that is the pixel 'grid' dimensions: 1200 pixels x 1600 pixels.
The next section is 'Document Size' - i.e. what size the image would print at. In this case over A3 size!
That's because the image is only 72 dots per inch (dpi) Resolution.
The dimensions for raw images from your own camera will be different to this according to its mega pixel rating.
Determine the image size you want. A rough guide would be:
Emailing pictures. Reduce their size to maximum width of an A4 sheet and only 72 dpi resolution. for small file sizes.
Inkjet printing pictures. Resolution is the key. A high quality inkjet needs a picture at 200 dpi resolution minimum. Set that value in the Resolution box first, then change the Document Size.
High quality brochure printing. If you ever have to supply pictures to a printer, they should be a minimum of 300 dpi at the size they will be printed.
Tip: It is always recommended to reduce the physical size of your image, if you are increasing the Resolution (dpi), otherwise you will be enlarging the size of the pixels in the image. That will show 'pixellation' on screen and in prints. Try the exercise below:
Try this resize with the bear image:
First change the Resolution to 200 dpi. (Note what Print Size the program automatically calculates)
Go to the 'Print Size' section of the dialogue box (highlighted on the left)
Make sure Inches is set as the measurement increment.
Then
change the width to 4.5 inches. Paint.net will automatically keep the proportions of the image and make the Height 6 inches. (Assuming the 'Maintain Aspect Ratio' box is ticked).
Notice how the Pixel dimensions have changedl (1200 x 900). This means that we have 'thrown away' pixels - so we won't be able to restore this image back to its original quality.
Click OK to change. We now have an 6 " x 4.5 " picture that will print well on a high quality inkjet.