The correct way to save a psd at High Res

Hi everyone i have a quick noob question for photoshop as i am still teaching myself. I have a project that will require me to make a 22in x 44in poster. i want it to be made as a 300dpi res file. I was told that to make it easier to work with i could make it a 150dpi and just change it to 300dpi when im finished. ive been doing some research and i know that if i save it as 150dpi i cant just change the resolution or that its not the proper way. So is it possible to save it as a 150dpi Psd so i dont lose my work but then do a Save as and save it as a different file and make it 300dpi ?

Thanks for all of your help in advance -Mike

 

It is possible... but it will depend on the art and graphics that will make up this poster and how you plan on creating it.

First... a 22in x 44in @ 150 dpi = 11in x 22in @ 300 dpi... which means you will be enlarging all the image details by 200 %. Any part done using Bitmap images (also known as raster images) are made up of pixels in a grid. Any enlargement will cause Photoshop to be guessing at the pixels needed to fill in any details as it resamples the image.

Some of Photoshop's tools are scalable and will retain the detail when you enlarge it from 150 dpi to 300 dpi... but if this poster will contain any elements that was not created with vector software (such as any scanned image / art / photo)... then you will be sacrificing a degree of image quality by enlarging it afterwards.

 

Thanks Very much for your reply. +Rep Given