when to resize

[jlcos1]

This may be the best site on the web for Canon users. I have learned a great deal from all you folks. I decided to register and ask a question of my own.
I have been using Pekkas' actions in photoshop and have been extremely happy with the results. But I have been reading that sharpening should be done after you re-size your image. In the actions, re-sizing is done as part of the actions. I usally resize my photos after the actions are run right from Photoshop. Like I said, I have been happy with the results but can I get even better results some other way. Any information that you could share would be appriciated.

[Timo Autiokari]

Hello jlcos1,

It depends... sometimes it is better to sharpen a little/slightly before resizing downwards and then to apply the final sharpening after the resizing, this will "preserve" (boost up) the finest image detail a little better. Also it depends on the noise level of the acquire device, with image data that has high noise level it is better not to sharpen at all before downsampling, it simply gives more noise after the resizing. Downsamling averages the noise somewhat so the apparent image quality in regards with the noise increases, but if one first boosts up the noise by sharpening then downsampling can not do the noise averaging correctly.

Usually it is not a good thing to do to sharpen before upsampling, it will exaggerate the edges.

In the Actions palette, when you turn it OFF from the Button -mode you can examine the individual steps in any of the Actions and you can deactivate any step you like by simply uncheking the "toggle item on/off" check mark.

Now, Pekka's Action does the sharpening in the linear domain, this is the only proper thing to do, gives the best possible result. I have the understanding the this Action releases the image in the particular working-space that the user has selected and this may not be a linear space so sharpening there will introduce Gamma Indused Errors, mainly white-edging, some hue shifts and very very weak sharpening in the dark end.