Extracting just a single tile out of JPEG file is a really big PITA There are about 27 different variants of JPEG (though not all really matter and are widely used)
Usually you've got 8x8 tiles in row-order, and because of entropy encoding you can not navigate just to random tile - you'll have to scan from the start ( maybe you can build index, where single block-rows start - this will make scanning easier ) In this case, there will be only 1000 rows, with 1000 block in them - performance may be adequate. On Nov 20, 11:32 pm, Robert Green <rbgrn....@gmail.com> wrote: > I'd solve this by writing a preprocessor that breaks that big file > down into manageable chunks. Think of having 10x10 array of 800x800 > images. I would also mipmap a 4000x4000, 2000x2000, 1000x1000 and > 500x500 of the file. Then, start the user on the correct zoom level, > using only the tiles you need of your arrays. OpenGL is actually > really good for this sort of thing. You could feasibly use 1024x1024 > pixel texture tiles with an orthographic projection and let it handle > the scaling. > > In short, I don't believe there is any way to get 8000x8000x16bit = > 128MB of bitmap data into 16MB of RAM all at once, but you can > definitely break it apart and work with pieces. A 1000x1000 pixel > piece consumes 2MB of RAM. You could have 4 of those loaded at once > and be OK on memory. If you're viewing actual pixels, you only need a > max of 4 loaded at a time to have seamless panning between them. > > On Nov 20, 2:38 pm, PJ <pjbar...@gmail.com> wrote: > > > We might be able to come up with more creative solutions if you give > > us more information about where the 8000x8000 jpeg file is coming > > from, and whether you just want to display it in a WxH view or to do > > something else with it. > > > Also, since you expressed interest in Google's server-side solution > > for Google Maps, are you considering developing a server-side > > component to your app as well? If so, you could host this capability > > (convert 8000x8000 image to smaller image) on a server somewhere. > > > If you try to do all processing on the device itself, it's probably > > going to be very slow. > > > What does your app do? Now you've got me all curious. :D > > > -- PJ > > > On Nov 19, 7:06 pm, James Wang <jameswangc...@gmail.com> wrote: > > > > > > Step #2: Generate 10,000 tiles that are 80*80 instead (100 * 100 > > > > > tiles). > > > > > > Step #3: Render tiles on-screen by drawing them on the Canvas, and > > > > > support swipe gestures to move through the image by replacing tiles, > > > > > much like Google Maps works. > > > > Hi Mark, AFAIK, the decoder of jpeg on android must support to read > > > random part of jpeg file if I want do step#2 as you said. > > > I checked out SDK reference and found out the default decoder of jpeg > > > seems not support it. Am I right? > > > Do I have to make another jpeg decoder? > > > > BTW, I think google map does the same thing on server side, not on > > > mobile phone, does not it? -- You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
