Hi folks,

Having a problem with "aliasing" -- little jagged edges -- in some images. Here's how: I tend to scan negs or prints at fairly high resolution cuz I like extra data/size when cleaning up dust and stuff and the high res also gives greater flexibility if I want to print later, for example. Anway to post in the galleries, I reduce these high res images in PS to 72 dpi and enter an appropriate screen size. But in photos with straight lines or especially text, these ugly jagged edges suddenly appear, even though everything else in the photo is very sharp and clear.

Is there a way to reduce large res images and avoid these jagged edges? Am I doing something wrong or is this unavoidable when resampling down a high res image?

Your wisdom and guidance is most appreciated! :) :)

When resizing for on screen I never look at DPI setting just the amount of pixels. Resizing method is set to bicubic. I've very little problems with aliasing. At some point you are going to get aliasing with near horizontal or near vertical lines, this is unavoidable because of the pixels you're stowing the info into. You could always rotate to fix a horizontal/vertical line so it's exactly aligned using the measure tool which is hidden under the pipet/colorsucker tool.

Attached Link: http://controlledvocabulary.com/imagedatabases/downsampling.html

Apparently my brain won't engage ... let me post this again...with correct link: Sounds like you are doing one big reduction in size. Try doing multiple size reductions in smaller steps. The link above is a really good article with a technique that works very well. I used the basis of this technique to create my own variation of this that I then put into a Photoshop Action that made its application automatic. The multiple steps involved in reducing the image should control your aliasing problem. Later I got Genuine Fractals, so I stopped using this technique (G.F. gave me much finer control over final image size). Of all the non-3rd party image downsampling techniques (and even over a couple of the commercial ones), this is the one I'd recommend. -=>Donald

Oh yea, one thing to remember. This technique uses changing the ppi to do its image reduction. Don't get hung up on that. The whole idea of 72ppi being what you need to go to is a bogus idea that hasn't been true for almost 20 years (still wonder why that idea persists). What he is doing is using the ppi to halve the image each time. That way, he isn't depending on an exact starting image size (but in a range of starting sizes). If youre scanner is neither 4000dpi or 2700dpi then you'll need to figure out what your starting ppi should be that will get you to the resolution you want the final image to be at when done. Did that make any sense? -=>Donald

Thanks everybody for the helpful feedback. Donald, I will definitely give that technique a try. But all those numbers make me a little nervous... I'm not much when it comes to math and calculation. So I'm intrigued by your mention of 3rd party techniques. Do you mean software that does the job automatically? Like as a plug-in in PS? Do you have the names of some of those programs/vendors? Many thanks again! :) Steve

Sure ... two that impressed me are: Genuine Fractals by LizardTech - http://www.lizardtech.com/ It uses fractal math to calculate the resizing (you save the image out at full size under their format and when you load it back in, you can set the size to whatever you want). XFile by HumanSoft - http://www.humansoftware.com As for the math, it only looks complicated. It really just comes down to every time you halve the ppi you halve the image size. As long as you remember that you'll be fine. :) -=>Donald

Hmm thats some good advice I use Photoshop save for the web function as it does a brilliant job without all the hassle! The only thing you have to consider is keeping the file sizes below the limits for the image and thumb. Danny