Resolution in Digital Images Vector versus Raster Why

Resolution in Digital Images & Vector versus Raster Why we work at 300 ppi in Photoshop and what that actually means….

Resolution • Resolution is another way to talk about image quality and, in Adobe Photoshop, we adjust our resolution by changing the ppi (AKA the number of Pixels Per Inch). • Higher number of ppi = higher quality • Lower number of ppi = lower quality

How it works • Photoshop is a RASTER based program, meaning it relies on pixels to convey the information that makes up images. • Photoshop can only place 1 color in a pixel and it has to fill the whole pixel. • Here is a 5 x 5” image at 1 ppi. • If I try to draw a circle it comes out like this:

• Here’s a circle on that same 5 x 5” square at 4 pixels per inch • And 16 pixels per inch 4 ppi 16 ppi

Each time I raise the resolution – the number of ppi – the image gets clearer We always work at 300 ppi – a good resolution for printing BUT you guys like to copy and paste images from the internet (most always at 72 ppi) on to your work to collage or alter. If you copy an image that’s 72 ppi and paste it into a file that’s 300 ppi, the image will appear very tiny. Why do you think this is?

• The higher resolution image can hold more information in less physical space, so the lower resolution image appears smaller because it contains less information. • Example: • a 5 x 5 image at 300 ppi = 2, 250, 000 pixels (2. 2 Mega pixels) • a 5 x 5 image at 72 ppi = 129, 600 pixels (0. 1 Mega pixels) • THUS, the 72 ppi image only takes up 129, 000 of the available pixels when pasted into the 300 ppi image (1/22 nd), leaving 2, 120, 400 (2. 1 M) empty pixels. • Ok, so why can’t I just free transform/stretch the small 72 ppi pasted image to fill the new 300 ppi canvas?

• Because the information about those empty 2. 1 M pixels is not available. The computer has to INTERPOLATE (guess) what should be in those pixels when you resize. • There are different formulas for interpolation, but none of them can bring back information that was lost or is missing, they can only approximate. • The computer can always maintain quality when sizing smaller, but cannot do so when sizing larger. • This is why we work at the highest quality setting possible, to ensure that our images are of sufficient quality for large prints

2 x 3 image at 300 ppi 2 x 3 image at 72 which has been pasted into a 2 x 3 image at 300 – note how much Empty information PS will have to Interpolate… The same 2 x 3 image at 72 ppi which has been PASTED INTO a 2 x 3 image at 300 ppi and now has been Free Transformed/stretched to fit YUCK! THIS IS WHY WE ALWAYS START AS LARGE OR LARGERTHAN WE WANT TO PRINT!

So what if I need an image? • In order to have appropriate quality, you’ll probably have to take the image yourself *gasp!* • This is better anyway because it avoids copyright infringement! • Professionals often subscribe to stock photo websites where you can pay to use high quality images. • You can also trace an image in Adobe Illustrator to create a VECTOR illustration which will be 300 ppi when imported into Photoshop – (make sure you have permission to use the image first or than you are changing it enough to make it your own!)

Vector based images • Remember I mentioned that Photoshop is a RASTER based program which relies on pixels to convey information. • Illustrator doesn’t do this. It relies on points, connected to curves or lines. • The computer reads the information in each point and can relay it to the line or shape. • Vector images can be resized to any scale with little to no quality loss.

VECTOR Portrait done in Illustrator at 100% Vector Portrait scaled to 800% Zoom showing each point in the vector – Each little colored Dot is a point, Connected to a curve or a line Portrait as a RASTER image Scaled to 800%

If Vectors are so great, why don’t we just work in Illustrator all the time? • While vectors are awesome at clean, smooth lines, they’re not so great at photo-realisitic detail. • The portrait shown was made up of thousands of points and still looks like an illustration. • Raster based programs are great for photo editing and realistic detail; just make sure your file is the appropriate size and resolution to start! • For what types of applications would a vector based image be a good choice?

What if my project has parts which work best in different programs? • Photoshop and Illustrator are compatible – they can open each others files. – Layers in PS will be flattened/merged when brought into AI or converted to objects – Shapes/Objects from AI will be merged when brought into PS • Thus, it is best to only swap programs once, rather than bringing an image back and forth.

By the end of this you should understand (and be prepared to discuss on your final…): • Resolution, Pixels per Inch, Raster • Interpolation and quality loss when freetransforming/stretching • Vector, Points • What applications are best suited to each program based on the above points.