Retaining photo quality when resizing

byline · Post by **byline** » 2007-01-13T22:35:42-07:00

We use ImageMagick for photo editing, OpenOffice for word processing. For some reason, when I reduce digital photos to the size needed to fit in a given space (or, for that matter, do any kind of editing, such as cropping, brightening, etc.), ImageMagick really zaps the resolution. I have no idea why. But when I use frames in OpenOffice, then insert the photo into the frame but keep the original photo as is (the frame automatically resizes the photo to the size I need), no resolution is lost.

When I manipulate a JPEG file and then save it, I get a field asking "Enter JPEG quality"; typically there is already a number entered there, usually 75; 75 of what unit? Even If I type in a higher value, such as 100, the resolution of the saved image is still greatly depleted. Also, a "Non-progressive" box is shaded in; should I de-select that?

Any suggestions anyone can offer are greatly appreciated. Thanks!

Post by **anthony** » 2007-01-15T22:49:13-07:00

The 75 is a factor into the JPEG compression algorithm the lower the number the worse the image looks but the smaller the file. even 100 (highest) will not preserve your image perfectly. Such is the JPEG format.

Resolution is controled in IM with -density. set it before you save the image you want to use.

byline · Post by **byline** » 2007-01-16T10:53:15-07:00

Thank you for your reply. At least I know what my max (100) is. As you note, when I type that in, the JPEG still loses some of its quality. I wasn't sure if that was because of ImageMagick, or the format, itself. Now I know. Thanks also for the info about density with regard to resolution. Where do I set the density value? I don't see it listed in any of the pull-down menus.

animesh_jain · Post by **animesh_jain** » 2007-01-16T11:31:33-07:00

I guess the fact that the image looks like it has lost resolution is because of slight blurring which takes place after resizing. Try applying the unsharp image filter after the resize operation, and you should get a sharper image.

byline · Post by **byline** » 2007-01-16T12:35:37-07:00

animesh_jain wrote: I guess the fact that the image looks like it has lost resolution is because of slight blurring which takes place after resizing. Try applying the unsharp image filter after the resize operation, and you should get a sharper image.

I'm at a loss to find this feature, as well as the previously mentioned density feature. Under "Effects," there is a "Sharpen" feature. Is this what you're referring to? I've tried that in the past, and sometimes it works, other times it doesn't. Those times it doesn't, it actually seems to make the photo grainier than it was originally.