Optimizing Images for OS X

March 28, 2006 11:00 AM

How should I format pdfs for best viewing in OS X's screen saver slide show?

I'm converting full broadsheet pdfs of a newspaper (12" x 20" at 266 dpi) into jpgs (or png's or tiff's) to be displayed on a Mac. No matter what screen resolution or image size I use, the type pixelates out when it gets displayed in the slide show screen saver.

Does anyone know of an optimum format &/or formula to use for the slide show default settings? Also, I want to keep the "ken burns effect" pans and scans of the newspaper pages (if possible).

posted by valkane to computers & internet (4 comments total)

That's a neat idea! You didn't talk much about what you'd tried... since nobody else has chimed in yet, I'll just talk about how I'd approach the problem.

First, if you display the image at the screen resolution, full size, but without the screensaver, does it also pixelate? Unless you have a really big monitor, I'm not sure you'd have enough pixels to make a full page of real text legible. I think you're saying it looks OK as a JPG, but then if you run it through Screensaver, it looks like crap.... but I'm not completely certain.

If it works without the screensaver, you're probably running into an artifact of whatever scaler it's using. I know it zooms in and out on images, so some pixelation is absolutely inevitable.

The Mac is a LOT more advanced with scaling than Windows is, but I'm not sure that the screensaver is using the same rendering engine.

With Windows, the things I'd try would be:

1. Make it a JPG (also try BMP [probably TIF on the Mac]) in exactly the dimensions as the hard screen resolution, and see what happens.
2. If that doesn't work, you *might* improve pixelation by making the width and height both a multiple of 256. If they're using a floating point scaler, that won't help, but if it's an integer scaler, sometimes it'll zoom more smoothly if you do that.
3. I don't know if it supports this, but the OSX scaler is really, really flexible, and if they were SMART, the screensaver will have tapped into that. You might be able to just specify your original PDFs as sources for your screensaver. PDFs should scale nicely to almost any resolution without pixelation.

I'd try it first on a small one you already have. If you can indeed use PDF sources in Screensaver, then make some in the same aspect ratio as your monitor (ie, cut down your newspaper PDFs), and you're home free.

I'd think you'd need a fast G5 or any Intel Mac to pull this off well... a G4 might have trouble scaling/panning a big PDF.
posted by Malor at 12:02 PM on March 28, 2006

The problem you're running in to is that OpenGL (which is used for the slides screen saver) is optimized for images, not rasterized text. Regardless of the image resolution or format, it's not going to look as crisp as the vectored text in a PDF.

What you can do to get the best possible look is use resoltions at least double that of your display (the higher the better), and use the PNG file format so you don't get any JPEG artifacts. Keep in mind that the DPI is not relevant in OpenGL -- only the total pixel count matters.
posted by pmbuko at 12:04 PM on March 28, 2006

Actually, I take that back. OpenGL can be quite good at keeping text very readable. I just noodled with Apple's Quartz Composer (part of Tiger's Developer Tools) and tried making a screen saver with hig-res images of text and was pretty successful. Somebody else made a better one, though and it's available here.

1. If you don't have Quartz Composer, install the Developer tools (on your OS X Tiger CD), then open the file from the second link in Quartz Composer (/Developer/Applications/Graphics Tools).
   
2. In the main window, you'll see a blue 'patch' called Folder Images. Select the patch, then click the blue 'i' on the right side of the window's toolbar to open the inspector.
   
3. Select Input Parameters from the menu on top of the inspector window, and then change the Folder Path item to point to the location where all your newspaper images are stored, and hit enter. (You should see the change take effect in the preview window.)
   
4. If you need to change the time between slides, select the green Input Splitter (Interval) patch, go to the inspector and select the Input Parameters option, and adjust the Input value.
   
5. Now you just need to save the change and move the quartz file into your ~/Library/Screen Savers folder (or /Library/Screen Savers to make it accessible to all users), then select it in the Screen Savers system prefs.

posted by pmbuko at 1:29 PM on March 28, 2006

Thanks pmbuko! I've also learned that 10.4's slide show will display pdfs at a really nice resolution, with no conversion needed. I guess I'll have to drag my poor G3 into the present....

Also, it seems if you export from a pdf as an eps in Acrobat, photoshop will make higher-rez .jpgs than I was getting using photoshop alone to raster up a pdf.
posted by valkane at 4:51 PM on March 28, 2006