Concept
Image is generally saved at 72 PPI resolution because monitor displays
the image with actual size on the screen at 72 PPI. The monitor resolution
is considered 72 DPI in general. If the image is scanned at 144 PPI,
it will be displayed with double size because 72 x 72 pixels will fit
in 1 inch. Rest of the 72 x 72 pixels will occupy double space. The
result is obvious, the double size of the original image.
1. Open Photoshop. Open an image with 72 PPI resolution.
2. Open the image size dialogue box to check the image settings.
Image > Image Size
3. Save the image
File > Save for Web
We have saved it with JPEG Medium 30 Quality. It is of 5.546 KB.
4. Open the image size dialogue box again to change the image settings.
Image > Image Size
Change the resolution to 144 PPI
5. You will notice that width and the height changes automatically into double figure.
6. Save the image with different name.
File > Save for Web
We have saved it with JPEG Medium 30 Quality. It is of 14.292 KB.
You can keep both the images side by side.
The image with 144 PPI occupies double space.
This tutorial is based on the discussion at Inside Graphics Group
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