Constructive adjustment/ posterise
Destructive to crop a image as this is a permanent change and can't adjust later
Specify size of image in properties bar and move image into document.
Adjusting brightness/contrast from drop down menu is destructive as cannot undo. Instead specify which areas want to alter using adjustment layers ie In layers panel chose image adjustment layer, can use mask layers to select an area. I this example I posterised only certain parts of the image.
Colour overlay with darken
Desaturate using masks
To create a layer adjustment mask
Select adjustment layer - hue and saturation
use a selection tool such as a magic wand or quick selection tool to chose area for adjustment.
When area chosen, ensure layer and mask are selected
Edit, fill, black (Can also select inverse of this )
Adjust hue and saturation as appropriate
Creating overlay and mask
Masks, tints and layers
Can make the whole image greyscale by desaturating
Create an adjustment layer
Hue & Saturation
Mask area you don't want black and white (here used rectangle)
Click on mask Edit, fill black
Back to actual layer desaturate.
To take away from mask fill with white
When creating files for first time always think about what the output will be ie CMYK for print or RGB for screen. So for example if a CMYK file is to go on your blog convert to RGB.