I've been importing my set designer's stage plot as a PDF into a layer on LX Beams. It usually is quite large at 300dpi and 24" x 36" for the main set.
I exported as the xml format and imported via itunes but the file takes a long time to render on the iPad2 iOS 6.1.3
If I zoom in/out the redraw time is too long.
I'll try and play with the PDF size & compression in photoshop, but I don't want to change the scale of my current plot.
Any recommendations on PDF compression to speed up redraw time in the app?
Recommended PDF compression settings
It is hard to say the nature of the PDF you are starting out with. PDFs can include vector and bit-mapped graphics. If you use Photoshop to edit the PDF, it is likely that you will change it into an entire bit-mapped image. Although, from the sounds of it, you may have a bitmap already.
You don't say how you got the original PDF into the file (using Mac or Windows). Because of the lack of operating system support for PDF graphics on Windows, all imported graphics in .lxxfiles are stored in either jpeg or png format. The storage format is chosen in the preferences/options of LXFree. If you import a PDF on a Mac, there is an additional option to store PDFs alongside the bitmap in the lxxplot file. If you open the file on iOS or another Mac, the PDF version is used. If you open the file on Windows or Linux, the bitmap version is used. This makes the file bigger. But, it preserves the maximum amount of information. This is only going to help if the original PDF is a vector type, and not already converted into a bitmap. In which case, you are just as well off to use the jpeg or png storage of the lxxfile.
So, if you have a large bitmap, you might try making a low resolution copy at 72 dpi and importing that into a separate layer. You could show the low resolution layer and hide the high resolution layer when you are just maneuvering around the plot, particularly on the iPad. And, switch back to the high resolution version for printing. This will increase the file size because you are storing two copies. But, it should increase the speed of the screen when showing the lower resolution layer. In making the lower resolution layer, you probably would be best to also do any scaling necessary. For example, if you started out with a 1/2" scale drawing and shrunk it by 50% inside LXFree so it would match LXFree's scale, you might be better off pre-shrinking in Photoshop so that the computer or iPad does not have to perform a scaling operation on the large amount of data every time the screen is drawn.
Part of the issue is going to be the way the iPad is optimized. The iPad stresses battery life over performance. That's why it takes so much longer to open a plot on an iPad vs. a computer. The only solution to this is faster processor and better battery. iOS 7 has started supporting 64 bit processors. And it is likely that iPads will get closer to computer speeds in the future.
You don't say how you got the original PDF into the file (using Mac or Windows). Because of the lack of operating system support for PDF graphics on Windows, all imported graphics in .lxxfiles are stored in either jpeg or png format. The storage format is chosen in the preferences/options of LXFree. If you import a PDF on a Mac, there is an additional option to store PDFs alongside the bitmap in the lxxplot file. If you open the file on iOS or another Mac, the PDF version is used. If you open the file on Windows or Linux, the bitmap version is used. This makes the file bigger. But, it preserves the maximum amount of information. This is only going to help if the original PDF is a vector type, and not already converted into a bitmap. In which case, you are just as well off to use the jpeg or png storage of the lxxfile.
So, if you have a large bitmap, you might try making a low resolution copy at 72 dpi and importing that into a separate layer. You could show the low resolution layer and hide the high resolution layer when you are just maneuvering around the plot, particularly on the iPad. And, switch back to the high resolution version for printing. This will increase the file size because you are storing two copies. But, it should increase the speed of the screen when showing the lower resolution layer. In making the lower resolution layer, you probably would be best to also do any scaling necessary. For example, if you started out with a 1/2" scale drawing and shrunk it by 50% inside LXFree so it would match LXFree's scale, you might be better off pre-shrinking in Photoshop so that the computer or iPad does not have to perform a scaling operation on the large amount of data every time the screen is drawn.
Part of the issue is going to be the way the iPad is optimized. The iPad stresses battery life over performance. That's why it takes so much longer to open a plot on an iPad vs. a computer. The only solution to this is faster processor and better battery. iOS 7 has started supporting 64 bit processors. And it is likely that iPads will get closer to computer speeds in the future.