Rotation of JPG file triples file size

[Sam Davis]

When I rotate a JPG left using the 'L' command. The rotation is correct and the pixels size is the same just rotated ie X by Y becomes Y by X, but the new JPG triples in size. Any ideas as to why.

24 bit color 5869 x 4768, Windows XP Professional, Irfan V4.25

[Bhikkhu Pesala]

I doubt very much that you have discovered a bug. The size of the JPG (on disk) depends very much on how much compression is used. You have probably opened a JPG file that was compressed with a medium or low setting, and saved it at the highest setting after rotating it.

Adjust the save quality on the JPG save dialogue slider to suit your requirements. I find that a setting of about 75 gives high enough quality for most photographs while keeping the file size small. A setting of about 50 is plenty good enough for photos for the web to reduce file sizes and speed up page loading for users on slow connections.

The highest quality, lowest compression setting of 100 need only be used where you don't wish to compromise at all on quality.

[derniwi]

For rotating a JPG in 90° steps you should use the "JPG lossless operation" from the option menu. Please make sure to remove the "Optimize JPG" selection (I don't know exactly what this does, but it changes the file size). Using the L or R key will rotate exactly as you wish, but saving the image will recompress the file.