image size, dimensions & resolution
in Photoshop
- Image size
- Web optimization
- Canvas size
- Cropping
- Color modes
- Transparent background
Proper image size is very important in all projects, whether they are intended for printing or for screen view.
Let's take a look at image size options.
Open your image in Photoshop..
Image size

To check (and edit) image's size and dimensions - go to the menu bar:
Image > Image Size
In the pop-up window you will see:
- Image preview window at 100% zoom
- Image size (file size)
- Dimensions of the image - in pixels, inches, cm, etc.... in your default units, that you can adjust in the Preferences menu
- Editable options for height and width (choose units). For the most part you want to keep them linked - so if you change one, the other will adjust to maintain the proportions
- Resolution - it shows the current one, but it's editable.

If you change resolution setting - the image pixel dimensions will change as well.
The dimensions of the printed image will not change (if you set the dimensions in inches, for example)
You can change the resolution to something ridiculously small to see how it changes the image.
Compare these two resolution settings:

Every time you change the image resolution or dimensions, you affect the image size. Pay close attention to all settings as you edit each one of them.
If you want to adjust the image (file) size - this is the first place you go to do so.

You can check the summary of your image file in the Properties panel.
Window > Properties
As long as you're there - check the color mode.
RGB - for screen and web
CMYK - for print
You can also get to the Color mode setting from the menu bar:
Image > Mode >
transparent background

There are times when you need an image with a transparent background.
After you open your image file - open the Layers panel (Window > Layers)
By default, you will have your image on the background layer, which is locked.

To unlock the background layer you need to rename it:
Double-click on the layer.
In a pop-up window rename the layer or leave the generated Layer 0 name.
Click OK.
Now the image can be moved inside the image window and parts of it can be removed.

When you remove a part of an image - a grey-and-white grid will show to indicate that this area is transparent.
.JPG format does not support transparency! .PNG does!
So you will need to export it as a .PNG file.
File > Export As

Change format to PNG
Check Transparency option.
If you preparing a file for web - check Smaller File option.
You can zoom in the preview to see the details and compare image quality.
Check the file size now.

You can also change the dimensions of the optimized image.

Click Export.
And that's it!