I posted yesteday about image resolution and image size, referring to pixel images (known as raster images).  I said that you cannot increase the size of the image without decreasing the image quality.  However there is one type of image that you can increase without loss of quality.  This is the vector image, and I will talk about these today.

The reason why vector images are so flexible when you resize them is that the resizing calculations are based on mathematical calculations for redrawing the image, rather than pixels.  For simple drawings and logos this means that file size can be restrained while producing very large images, with no loss of quality.  To produce large pixel based high quality images you end up producing extremely large file sizes.  It is possible to convert vector images into raster images, but the results are often less pleasing when you try to convert raster images into vector images with a loss of flexibility that you get with the original.  Therefore it is best to get the original artwork or logo as a vector image.  In fact it is probably a good idea to get both versions of the image because many programmes are not able to read or open vector images.  If you want to produce vector images you will need a specific drawing programme such as Adobe Illustrator or Corel Draw.  If you are looking at developing illustration skills developing your skills in one of these packages is essential.

Here is a very easy to follow article on the suject for those who want more detail.

A colleague was printing out an image that she received and noticed it was pixelatted.  By this I mean that you could see zigzag edges where there should have been smooth ones.  The subject of image quality can be quite complicated because when you see an image on the screen it looks perfect, but you print it out and you get lots of rough edges and generally poor quality.  So here's an explanation for this.

The issue here is one of image resolution.  This is the quality of the image which is measured as pixels per inch or PPI.  Pixels are tiny squares that are usually not visible to the eye, and most images (except vector images which I will talk about some other time) are made up of a number pixels.  An image that has 100 pixels across the top and 100 has a total of 10000 pixels.  If this particular image measures 5 inches than it has 20 ppi.  If it measures 10 inches then it has 10 ppi because it has the same number of pixels in a bigger space.  Most computer screens reproduce an image at 72ppi, so any image that has that resolution or higher will be viewed perfectly.  A home printer may print out at 150 or 200ppi.  If your image is that resolution or higher it should print out well.  If your image is only 72ppi it will not print out well and you will probably get pixelation.  A high end printer needs 300ppi, so if your image is only 72ppi it will look very poor.

You can use an image editing program such as Photoshop to squeeze the pixels together to make a higher resolution image, so for the example above to achieve a 72ppi image your image would come down to 1.38 inches.  To make your resolution higher for printing you would have to reduce the size even further, which is this case is not worth while.  Here is a more likley example  (note that it is still common to use the phrase ppi even though we are metric now - don't know why).  Say you receive an image that measures 10cm square at 72ppi.  If you use an image editing programme to change the resolution this is what you would get:

72ppi = 10 x 10
150ppi = 4.8 x 4.8
300ppi = 2.4 x 2.4

When you increase the quality of the image by increasing the resolution you reduce the dimensions.  It is technically possible to resample the image in an editing imaging programme.  Resampling means removing pixels, or adding them in, to an image while keeping it the same dimensions.  This works fine when removing pixels, but if you try to add them in the programme has to make up pixels and guess where to put them.  It is unlikely you will get a good quality result if you try this.  My recommendation is that if you need to print an image at a higher resolution than you have been given, go back to your source and ask for a copy with a higher resolution.  Unfortunately this is a much misunderstood area and people will often send you images that look lovely on screen, but awful when you print them.  You will get the best results if you get good quality images to begin with.

Here is a link to a much more indepth explanation of the relationship between resolution, screen size and printing if  you are interested.

I did promise last week a post on improving your selections in Photoshop, as a round up on this topic.  I am using Photoshop Elements 6 so the techniques might be slightly different in other versions, but the principles are the same.

When you make a basic selection using one of the techniques mentioned in previous posts, if you make a change to the selected area the outline can seem a bit sharp, a bit like someone has taken a pair of scissors to the image and just plonked the newly edited section down on top.  The way around that is to 'feather' the selection.  This is an image editing term which really just means to soften the edges a bit to blend in with the unedited parts of the image.

When you have made the desired selection, go to the Select menu and choose Feather.  Most selections will benefit from 1 or 2 pixels, but if an image is really big you might need to make it 5 or 6.  Click on OK and you selection will be softened.  Continue with your editing.  If the result is not as smooth as desired, use your Undo History palette to step back and redo the feathering with different settings.

For more flexibility go to the selections menu and choose Refine Edge.  If you wish click on the custom overlay button at the bottom left which will put a red mask over the unselected area allowing you to see more clearly how your edges are affected by your adjustments in the window.  You can now experiment with the sliders to get the desired results (when you hover your mouse over each slider a description is provided at the bottom of the dialogue box. 

Feathering has already been covered, but you can use the contract/expand slider to remove edges, sometimes referred to as 'fringing' where you get a white edge around your image.  When you have made your adjustments, click on OK and make your changes.  Again, use you Undo History if necessary to fine tune the process.

It really is worth taking some extra time to get this part right.  The results will be much more realistic (if that is what you are looking for!)

The tools we looked at in the last two posts can be used to make global changes to your photos (meaning you change the entire image).  However you can also use them to make changes to parts of your image.  The trick is to select the area you want to change, and then use the tool as directed.  Here's how to select (again these tools work in most other image editing programmes).

The selections tools in Photoshop Elements are in the second segment down on the toolbox on the left (assuming your settings are the default layout).  This is what they look like:

Starting from the top, the first tool is the square/eliptical selection tool, and you can see them both in the flyout menu.  Some of the tools in the toolbox share a location and you can identify these by the little triangle in the bottom right.  Click on this triangle and you will get a flyout menu such as shown in the screen shot above.  Select the tool you want to use, move the mouse over your image, click and drag and you should get a dotted line (aka marching ants) surrounding part of your image.  This selected area is the part of the image that will be altered.

The second set of tools are for selecting areas that are less uniform in shape.  The first in the set of three is useful for doing freehand selections.  The second one in the set is the magnetic selection tool and it will follow a line in colour difference.  Over your image, click, release the mouse button, and move the mouse along a line of colour and it will automatically lay down a selection line along the edge of the colour.  The third button down is the polygonal lasso tool.  Click over your image, release the button, move to a new location and press the mouse button again and it will put down a new anchor point.  To remove anchor points press the delete key on your keyboard.  To close up a selected area, double-click.

The final, but most powerful of the selection tools is the magic wand.  This selects pixels in your image of a particular colour.  

When you select this tool, look to the toolbar at the top of the window.  

If you put a tick next to Contiguous it will only select pixels of that colour that are touching.  If you leave the box empty it will select all the pixels of that colour in the image.  Change the tolerance setting to alter the sensitivity of the colour selection.

That's an overview of selection techniques. It is an important skill so I recommend you familiarise yourself with these tools.  Next week I will cover how to refine your selections so that your edits don't look obvious.