Rotate effect on image quality

[PaulT]

Does rotating an image.tiff affect image quality ?

[JendaLinda]

It depends on the color depth and compression used in the source TIFF.

[PaulT]

My images are grey scale, uncompressed tiff

[JendaLinda]

If it's just 8 bit grayscale, rotation in 90° steps won't affect image quality.

[PaulT]

how about 1 degree step ?

[JendaLinda]

A digital picture is made of pixels arranged in a grid. If the picture is rotated by an arbitrary angle, many pixels won't be aligned to the grid, so there will be imperfections. So rotating a picture by an angle other than multiples of 90° will decrease the image quality.

[PaulT]

That is very clear, thanks.
My application is deskewing some scanned black and white images prior to digitising them.
It seems careful examination of the detail is required to assess damage after rotating a few degrees.

[j7n]

What will be affected the most are sharp brightness transitions found in text or artificial shapes. You could scan such images at a higher resolution prior to rotating to decrease the high frequency content, or in other words, make the transitions more gradual. Scan to greyscale instead monochromatic black and white. If the images are too large, downsample by 2 after rotation.