resolution and quality issues

[alin33]

I'm creating digital art in gimp which is printed in big sizes also(18"x24" 300 ppi).When I create the art I give the max dimensions to the image(18"x24" 300 ppi)
Now there are additional graphics and elements I want to add to the image-the graphics I want to add are 300 dpi but smaller in image size-so I need to scale them-so they fit my big document-I'm afraid that during the scaling of the outer graphics their quality will be lost-I'm trying to understand what happens to resolution if scaling-My main concern is the quality of the digital art-the final product-I need it to be 300 ppi at big size(18" 24")so just want to understand the wise way to use external graphics -and how to scale them without harm to the resolution and quality-I'm trying to understand what happens to the quality when I scale this external graphics-do they lose their quality? Does their resolution change? Does resolution in general changes during scaling?

[Blighty]

The important thing to know is that Gimp (and all bitmap editors) work in pixels and not in units such as inches or ppi.

If you require an image 18"x24" 300 ppi then you need an image size of
(18x300)x(24x300)
=5400x7200 pixels

When you add additional graphics look at the size of these graphics in pixels. Other units are irrelevant. Compare the size of these graphics to your image size of 5400x7200 pixels

You will probably need to scale these graphics to the required size. But remember when scaling bitmaps there is always a loss in quality. If you scale down pixels are thrown away. If you scale up some algorithm creates new pixels. The more you scale the greater the loss in quality.

[rich2005]

Quote:I'm trying to understand what happens to the quality when I scale this external graphics-do they lose their quality? Does their resolution change? Does resolution in general changes during scaling?

do they lose their quality? - see Blighty's reply on scaling up and down and working in pixels.

Does their resolution change? The image resolution pixels-per-inch (ppi) only applies when you come to printing. It is set when you create a canvas and in Image -> Print Size Copying the "external graphic", either by copy/paste or File -> Open as Layers takes the resolution ppi setting of the "copied into" (your first) image.

Does resolution in general changes during scaling? No. The resolution setting is not changed during scaling.