Develop Reference

JPEG images have different pixel values across multiple devices

I had noticed that when reading in an identical photograph across devices in the JPEG format, the pixel values do not match up. They are close, but different. When converted to PNG files, the pixel values seem to match up.
This would seem that it would be due to the (un)compression algorithms across devices. That's what comes to mind anyways. Is there a way to read in JPEG files so that the same pixels are retrieved from the photograph across devices? I don't see an option within the BitmapFactory Options component.
Currently applying the following to maintain size when working on pixel values of an image across devices:
Options options = new Options();
options.inScaled = false;
options.inPreferQualityOverSpeed = true;
Currently comparing pixels with the following just to look at a few (close matches, but not equal):
int[] pixels = new int[bitmapF.getWidth() * bitmapF.getHeight()];
bitmapF.getPixels(pixels, 0, bitmapF.getWidth(), 0, 0, bitmapF.getWidth(), bitmapF.getHeight());
Log.d("pixel entries", "pixels = " + pixels[233] + " - " + pixels[4002] + " - " + pixels[11391]);
Note: If reading in a PNG version of that same file which is uncompressed, the values are identical as expected.
The Samsung Galaxy S4 for example and the Samsung Galaxy S5 even have different pixels from the same jpeg (running off of the same test activity) stored in the assets folder.
pixel[233] for instance would be -5205635 on s5 but -5336451 on the s4. The pixel[4002] is a little off as well. But pixel[11391] are equal across both devices on this jpeg picture.

The JPEG standard does not require that decoder implementations produce bit-for-bit identical output images. Unfortunately the standards document specifying decoder requirements, ISO 10918-2, is apparently not freely available online but Wikipedia says:
...the JPEG standard (and the similar MPEG standards) includes some precision requirements for the decoding, including all parts of the decoding process (variable length decoding, inverse DCT, dequantization, renormalization of outputs); the output from the reference algorithm must not exceed:
a maximum 1 bit of difference for each pixel component
low mean square error over each 8×8-pixel block
[etc.]
Differences between different decoder outputs using the same input are generally due to differing levels of internal precision, particularly in performing the IDCT. Another possible source of differences is smoothing, which attempts to reduce "blockiness" artifacts.
Like you, I would expect that setting inPreferQualityOverSpeed would produce the same output but nothing actually guarantees that. I can think of at least a couple ways that you could get small variations on two different phones:
The phones may run different versions of Android where the implementation of BitmapFactory changed (e.g. perhaps inPreferQualityOverSpeed was broken and then fixed, or vice versa), or
The phones may provide different hardware features (e.g. vector instruction set, DSP co-processor, etc.) that BitmapFactory leverages. Even differences in scalar floating-point units can cause discrepancies, especially with JIT compilation producing the actual machine instructions.
Given the wiggle room in the standard plus your experimental observations, it appears the only way to guarantee bit-for-bit agreement is to perform decoding within your own application. Perhaps you can find some alternative Android-compatible library.

I suppose you should also check if compressed PNGs appear the same way across devices.
http://pngquant.org/
If the answer is yes, then the only thing remaining would be to figure out how to convert programmatically on the phone those images to that same kind of compressed png.

Much of a JPEG decoder's work involves real number calculations. Usually this is done using fixed point integer arithmetic for performance. This introduces rounding errors. Slight variations are a natural part of working with JPEG.

Yes, the pixel color values are different across devices. This is very annoying especially if you want to compare colors. The solution is to compare visually equal colors (by human perception).
One of the best methods to compare two colors by human perception is CIE76. The difference is called Delta-E. When it is less than 1, the human eye can not recognize the difference.
You can find wonderful color utilities class (ColorUtils), which includes CIE76 comparison methods. It is written by Daniel Strebel,University of Zurich.
From ColorUtils.class I use the method:
static double colorDifference(int r1, int g1, int b1, int r2, int g2, int b2)
r1,g1,b1 - RGB values of the first color
r2,g2,b2 - RGB values ot the second color that you would like to compare
If you work with Android, you can get these values like this:
r1 = Color.red(pixel);
g1 = Color.green(pixel);
b1 = Color.blue(pixel);

Re-size the media to the required size or use HTML attributes to disable scaling of the image.
Another option would be to allow the user to decide after loading a thumbnail representation to save bandwidth.

I was having the same problem.
PNG and JPEG images seems to be rendered with approximation by different devices.
We solved the problem using BMP images (whose dimensions are unfortunately a lot bigger).

image noise reduction in android

I've written a camera app which allow users to capture image of paper bills, send to server where it'll be printed.
Problem:
when I print the image, the background is blackish due to noise in captured image. All I want is a clean white background. I've tried Bitmap's compress method to save the image in JPEG/PNG format on different scales (1-100) but not much helpful. I've seen camscanner app doing this fantastically but have no clue how.
Any pointer to achieve this will be helpful.
thanks.

If the issue is some random noise, there are some noise removing filters out there you can use (i.e. median filter or a bilateral filter).
Is the image already binarized (converted to strictly black and white pixels)? You'd want to do the filtering before this.
EDIT(after clarification on dark gray): Since the background is a dark gray I'm guessing the problem is just that it is a low contrast and since it will be a natural image, there will be variation on how bad the contrast is. I suggest using Sauvola binarization for this which will separate out the black and the dark gray to black and white. Here is some detail and example results of Sauvola: http://www.leptonica.com/binarization.html. To run some tests to see which binarization algorithm would be best you can find a library here

Changing compress ratio cannot give any help to this question. A strong filter will help you reduce the noise.
Try to have a look at this Link

Color banding only on Android 4.0+

On emulators running Android 4.0 or 4.0.3, I am seeing horrible colour banding which I can't seem to get rid of. On every other Android version I have tested, gradients look smooth.
I have a SurfaceView which is configured as RGBX_8888, and the banding is not present in the rendered canvas. If I manually dither the image by overlaying a noise pattern at the end of rendering I can make the gradients smooth again, though obviously at a cost to performance which I'd rather avoid.
So the banding is being introduced later. I can only assume that, on 4.0+, my SurfaceView is being quantized to a lower bit-depth at some point between it being drawn and being displayed, and I can see from a screen capture that gradients are stepping 8 values at a time in each channel, suggesting a quantization to 555 (not 565).
I added the following to my Activity onCreate function, but it made no difference.
getWindow().setFormat(PixelFormat.RGBA_8888);
getWindow().addFlags(WindowManager.LayoutParams.FLAG_DITHER);
I also tried putting the above in onAttachedToWindow() instead, but there was still no change.
(I believe that RGBA_8888 is the default window format anyway for 2.2 and above, so it's little surprise that explicitly setting that format has no effect on 4.0+.)
Which leaves the question, if the source is 8888 and the destination is 8888, what is introducing the quantization/banding and why does it only appear on 4.0+?
Very puzzling. I wonder if anyone can shed some light?

Try dis..
BitmapFactory.Options options = new BitmapFactory.Options();
options.inPreferredConfig = Bitmap.Config.ARGB_8888;
Bitmap gradient = BitmapFactory.decodeResource(getResources(), R.drawable.gradient, options);
findViewById(R.id.main).setBackgroundDrawable(new BitmapDrawable(gradient));

Turning on the emulator "Use Host GPU" option fixed the color problems for me, credit goes to this answer https://stackoverflow.com/a/17166234/1287459
In my case I was using Android 4.2.2.

Single Pixel Color Correction

I've created an android application that produces an image as output. This image has pixel errors that are unavoidable. Images are held in an integer array with a size of the image's length*width. The pixels are in ARGB8888 color configuration. I've been searching for a method to both find and approximate what the correct value of the pixel should be based off the surrounding pixels. Here is an example output that needs to be color corrected.

Median filter is your best friend in this situation. This is called salt-and-pepper noise.

That doesn't look (or sound) like what is normally meant by "color correction". Look for a despeckle algorithm.

Gaussian filter might work, or Crimmins Speckle Removal. You'll probably want to understand how Kernel Filters work.

Android 2.2 distorts picture colors?

I have some .png files in my app. I need to load these during runtime, and get the exact colors of certain pixels from them. It's important, that I do not want to scale these pictures. I don't show them on the UI directly, they serve as maps.
Now, on Android 1.5, there's no problem with this. I put these images in the '/res/drawable' dir, load them with BitmapFactory into a Bitmap object, and use it to get the color of the desired pixels. E.g. pixel (100, 50) has the color RGB(100, 1, 100).
On Android 2.2 tho, the same procedure results varying colors (for the same pixel), so I get RGB(99, 3, 102) / RGB(101, 2, 99) / etc. for the same (100, 50) pixel. I checked the resolution of the Bitmap object, it seems that is didn't get scaled.
Could somebody explain, why I get distorted colour values?

Solved: It appears, that on Android 2.2, I have to set the correct bitmap configuration. Somehow, versions below 2.2 managed to do this (or maybe fewer configs are supported on those, and the system guessed the config correctly, don't know).
Anyways, here's the code I use now:
BitmapFactory.Options opt = new BitmapFactory.Options();
opt.inDither=false;
opt.inPreferredConfig = Bitmap.Config.ARGB_8888;
Bitmap mask = BitmapFactory.decodeResource(getResources(), R.drawable.picture, opt);

Go make yourself a bitmap thats entirely the same color of the pixel in question. Make the size of this bitmap the same resolution of the one your currrently using. Load it up and check the RGB values of the same pixel (or any pixel) you are having problems with.
This should tell you whether your problem is either scaling, which is what I think it is, or possibly a problem in the color translation.

If you don't find an answer quickly, my pragmatist streak would ask how hard it is to parse the .png yourself, to get completely deterministic results independent of any changes in the platform.

My 2.3 devices (Nexus One and S) worked fine without setting "opt.inPreferredConfig", but it appears that 2.2 requires it for accurate RGBs.