Develop Reference

How to improve image quality for OCR reader in Android

I've made an app which uses the phone's camera to take a photo and then parses this photo (with Tesseract OCR) into a string.
The problem is that the string I obtain is very ugly, it contains wrong or unreadable characters.
I've read here that a filter to reduce image's noise may improve OCR's result. I've googled some of them and I've found this website which contains a lot of image filters written in Java. The issue is that they use BufferedImage class, which is not in Android SDK.
Does anyone know any other library which performs this operation in android?

You should use Bitmap. https://developer.android.com/reference/android/graphics/Bitmap.html
It's the equivalent (in theory, not in api) with BufferedImage.
Chek this post too:
How to load BufferedImage in android?

Opencv with Android- OCR

I want to do OCR for Sindhi, in an Android application, the idea is to let the person write on screen and then capture up the frame and then compare it with the images of the words pre saved in the mobile, and the image that matches up the most(using FLANN?) with the frame would have some text against it, and I just want to pronounce that text then. So please tell me if my approach is wrong, as I am new to Android and OpenCV both, or else tell me how do I start?

If I understand well your aim, you want to compare the text written on the screen of the mobile with images where text is present, right?
I've done a bit of OCR on Android and I used OpenCV and Tesseract.
Tesseract is a real OCR engine but you need to have images that are as "clean" as possible. That's why you need OpenCV to clean them up before using Tesseract.
OpenCv for Android : http://opencv.org/platforms/android.html
Tesseract for Android : https://github.com/rmtheis/tess-two
So to give you the main lines of my workflow for a similar application :
Grab the text written by the user in a string or an array of strings.
Go fetch your pre-saved images
Process them through OpenCV, OpenCV is mainly used here to clean the images by getting rid of noise especially. You should try using a Glaussian Blur, then an Adaptive Threshold and a Bitwise-NOT (OCR engines deal better with black and white images that you obtain with the Bitwise-NOT)
After you get some clean images with OpenCV, process these images through Tesseract. That will give you a string for each image that contains the detected text on the images.
Compare your different strings gathered on Tesseract with the user's text by parsing each word to find out the text that matches the best.
For the audio part of your app, I'm not sure how to proceed, they must be some libraries out there that might help.
You must be aware that using all these libraries on Android is quite a struggle, you might have problems with the build of the project, follow well the different documentation that is provided on the official websites.

Overlay Image on Live Camera feed using Wikitude

I have gone through all the samples of wikitude. Is it possible to overlay live camera feed image which has been saved as screenshot and create augmenetd image? If it is possible then what tracker image should I use? Because tracker image is the one which I know presently that which image I am going for track. Then if the image will be taken in future how can I create a .wtc file for that and how can I augment my camera feed? Is it possible in wikitude?
I have to create one application using wikitude. I like the sdk of wikitude.

If I understand you correctly you are looking for a way to create target images (that are used for recognition) on the device. This is currently not supported. However if you have a valid business case we are able to provide you with a server based tool to create target images. For more information please contact sales#wikitude.com.
Disclaimer: As you probably already guessed, I'm working for Wikitude.

Annotations of pdf using MuPDF on Android

I am developing an android application which should help users to annotate the PDF file. I am using MuPDF to parse the PDF on android device. I am able to read the PDF but unable to figure out a way which will help me implement annotations features for the PDF. I couldn't find any sample core nor could I find any manuals that explains what I am looking for. Anyone have any sample code, any other material or any links which will give me an idea on how can I support simple annotations (say draw a rectangle or write freely) on PDF files.
Any kind of help in this regard is much appreciated.
Thanks in advance.

You CAN draw annotations by completely delegating into the MuPDF library.
The sample app provided my them includes code for this.
The method in the native layer of MuPDF supporting this is addMarkupAnnotationInternal(int page, PointF[] quadPoints, int type)
The passed PointF[] defines the rectangle that you want to annotate. This is likely to come from a the text the user has selected.
If you are using the java wrapper that they provide, com.artifex.mupdfdemo.MuPDFCore.java, they provide the method called:
MuPDFCore#addMarkupAnnotation(int page, PointF[] quadPoints, Annotation.Type type)
To see how it is actually done and how the MuPDFCore#addMarkupAnnotation receives the quadpoints from the selection of the user, try the sample app while reading the code.
Basically, for adding an annotation you need to:
1- provide a list of points (quads) defining the box and the page of the highlighted area.
2- delegate into the MuPDF library by using the aforementioned method to add the annotation to the document and to render it.
For the first step, you will likely want to let the user select the area of the document to highlight. If so, you can let the user select by starting selection mode with:
MuPDFReaderView#setMode(MuPDFReaderView.Mode.Selecting);
and when the user finishes, get the selection with:
MuPDFView#selectText();
Doing all of this is not straightforward and you need to understand the API, so, I really recommend you to read the sample code.
In regards as where do you save the annotations, that is another story. You can save them in the PDF file (MuPDF lets you doing this) or you can store them anywhere else, which will require more code and will dissociate the annotations from the PDF file.
So, you can do it entirely with MuPDF, there is no need to draw the annotations as another layer to the Canvas/View using the Android API.

Do you want to store the annotations in the PDF file or separately?
The former is not possible with muPDF.
However, if you intend to store the annotations separately, then you could conceivably render the PDF to a canvas as background and then draw over it. You'll still have to write the equivalent of a drawing app. There's "FingerPaint" in the Android samples, and also Android Paint in open source.
If you want to highlight specific text in the PDF, things will get quite complex. You'd have to extract the character dimensions from fitz and manage a cursor of sorts in your touch handlers. This isn't impossible, but far from trivial.

Is there any way to synthesis image in Android native API or using HTML5

I want to build a mobile app with the following function:
Let user choose an image, then we generate a picture base on that picture.
The generated picture has some specified text with specified font.
There is another picture, which may be a PNG file, used as foreground.
Output that generated picture to user's device.
Is there any way to synthesis image in Android API or using HTML5?
I prefered use some Javascript way to do this, so I can easily build the app cross platform, but I don't know whether JS can do that.

For this purpose you can use HTML5 canvas https://developer.mozilla.org/en/Drawing_Graphics_with_Canvas
If you want to code this using Android API you can use Canvas:
http://developer.android.com/reference/android/graphics/Canvas.html
By the way there is a good guide "Displaying Bitmaps Efficiently" http://developer.android.com/training/displaying-bitmaps/index.html