Develop Reference

Renderscript, image processing, assigning pixel values from a precomputed array

I have an array of precomputed intensity (computed using a fuzzy logic inference system on a desktop machine). Now I want to use this array as a lookup table for a contrast enhancement application on android, using renderscript.
What I want to do, at a highlevel is to process every pixel in an image, and using the lookup table create a new image where the pixel at the corresponding position has the value looked up in the array. Before I start looking at how to implement this, is this even feasible?

Yes, it is feasible and this is something RS can handle with no problems. You'll need to provide your RS "kernel" with the pre-computed array data as either a separate Allocation or just a data array.
This talk will help get you started: https://youtu.be/3ynA92x8WQo

Android turn 3 sequence byte[] to int[]

I am looking to transfer pixel data from a server to an android program. On the server, the pixel data is in form RGBA, with one byte per color / transparency. Unfortunately on android the the corresponding pixel format is ARGB, meaning the alpha channel comes before the color data, instead of after, like it does on the server. I am worried that shuffling the RGBA data to ARGB format on the server will be too slow, and so I was hoping to find another way around that. The server is written in python by the way. I am capturing the screen data using the function presented here: Image.frombuffer with 16-bit image data. If there is a way to grab screen capture using this method (or some other) in ARGB format or even RGB_565 I would love to hear about that as well.
One trick I thought of to solve this problem was to use the isPreMultiplied flag on canvas.drawbitmap(int[], ...) and then send only the RGB bytes from the server. Then I could recompose the RGB bits into ints on the android device and send that to drawbitmap, ignoring the alpha channel entirely.
However, this leaves me with another problem. Ints are comprised of 4 bytes, and I have a sequence of 3 bytes in my byte[] array (the RGB values). I was using some of the solutions proposed here: byte array to Int Array to convert my byte[] to an int[] when I was transferring RGBA data. But now that it is just 3 byte sequences, I'm not sure how to quickly convert it to ints. I am hoping for close to real time image updating so I need a way to do this quickly. Any ideas?

int rgbInt = byteArray[0] << 16 + byteArray[1] << 8 + byteArray[2];
// not sure these are in the correct order, you may have to swap the indexes around.
You might also need to include
+ 0xFF << 24
to set the alpha value to opaque.

How to random read raw resource file in Android

In my Android project, I have a 2M-bytes raw data file. Since my application is a long-life app, I don't want it to always seize 2M memory. The data file has been formatted, once I need to some data from the data file, I just need to seek to some position and read several bytes.
The Resource class can only return an InputStream on raw file, but InputStream cannot do random read.
Is there a way on Android to random read some bytes from the raw data file? Or I have to read the entire file into memory when I only need a few bytes.

InputStream can skip bytes with skip() can also mark an offset with mark(), on reset() it can go back to marked position. All that can be used to do random IO.
You can store byte offsets in a separate lookup file as well.

Android is built upon Java so take a look at this tutorial:
http://docs.oracle.com/javase/tutorial/essential/io/rafs.html

define Bitmap bytes count and set limit to bitmap buffer

In my application I have an image viewer and I am getting bitmaps from web server.
In order to increase the performance of my app, I have a buffer of bitmaps.
The max size of one bitmap can be 0.5mb.
I have bufferSize variable where I want to store the buffer bytes count and therefore I need to know
each Bitmap size which I am going to add in buffer.And if the bites count exceed some X number I delete the bitmap from front of buffer.
And here is my problems:
I don't know how to define bitmap bytes count
I need a suggestion about X number .
Thanks in advance.

You can get the number of bytes in a Bitmap using the getByteCount() method.
Depends on how much memory your app is using, how many images you are retrieving from the web server, and how often you need to display them. Use some fraction of System.maxMemory(). In any case

Can large String Arrays freeze my program?

I recently created a program that gets medi-large amounts of xml data and converts it into arrays of Strings, then displays the data.
The program works great, but it freezes when it is making the arrays (for around 16 seconds depending on the size).
Is there any way I can optimize my program (Alternatives to string arrays etc.)

3 optimizations that should help:
Threading
If the program freezes it most likely means that you're not using a separate thread to process the large XML file. This means that your app has to wait until this task finishes to respond again.
Instead, create a new thread to process the XML and notify the main thread via a Handler when it's done, or use AsyncTask. This is explained in more detail here.
Data storage
Additionally, a local SQLite database might be more appropriate to store large amounts of data, specially if you don't have to show it all at once. This can be achieved with cursors that are provided by the platform.
Configuration changes
Finally, make sure that your data doesn't have to be reconstructed when a configuration change occurs (such as an orientation change). A persistent SQLite database can help with that, and also these methods.

You can use SAX to process the stream of XML, rather than trying to parse the whole file and generating a DOM in memory.

If you find that you really are using too much memory, and you have a reason to keep the string in memory rather than caching them on disk, there are certainly ways you can reduce the memory requirements. It's a sad fact that Java strings use a lot of space. They require two objects (the string itself and an underlying char array) and use two bytes per char. If your data is mostly 7-bit ASCII, you may be better of leaving it as a UTF-8 encoded byte stream, using 1 byte per character in the typical case.
A very effective scheme is to maintain an array of 32k byte buffers, and append the UTF-8 representation of each new string onto the first empty space in one of those arrays. Your reference to the string becomes a simple integer: PTR = (buffer index * 32k) + (buffer offset). "PTR/32k" yields the index of the desired byte buffer, and "PTR % 32k" yields the location within the buffer. Use either an initial length byte or a null terminator to keep track of how long the string is. When you need to access one of the strings, don't allocate a new String object: unpack it into a mutable StringBuilder or work directly with the UTF-8 byte representation.
The above approach is obviously a lot more work, but can save you between a factor of 2 and 6 in memory usage (depending on the length of your strings). However, you should beware of premature optimization. If your problem is with the processing time to parse your input, or is somewhere else in your program, you could find that you've done a lot of work to fix something that isn't your bottleneck and thus get no improvement at all.