Hi there
Ive noticed that when saving a few pictures as JPG for the web, the optomised image appear much larger than the actuall origional. I had to reduce the file size in another program, and ideas on what may be causing this ??
Optomised image appears larger than origional image
-
Masami
-
keenart
If you have an original image that is 144 dpi, and you save the image in a jpg that may reduce the resolution to 72 dpi, you are effectively enlarging the image by a factor of 2.
In other-words the 72 dpi pixels are stretched to occupy the same area that a 144 dpi previously occupied.
Therefore, if the original image was 1 inch by 1 inch, it will now be 2 inch by 2 inch. The original 144 dpi must now occupy more than 72 dpi for the full image to display, so the image is at half the original resolution and twice the image size.
The file size is reduced becasue there is less pixel information to store, also a compression scheme is applied, further reducing wasted space compressing the file even smaller.
In other-words the 72 dpi pixels are stretched to occupy the same area that a 144 dpi previously occupied.
Therefore, if the original image was 1 inch by 1 inch, it will now be 2 inch by 2 inch. The original 144 dpi must now occupy more than 72 dpi for the full image to display, so the image is at half the original resolution and twice the image size.
The file size is reduced becasue there is less pixel information to store, also a compression scheme is applied, further reducing wasted space compressing the file even smaller.