Android: Taken photo is bigger than the preview

问题:

I'm trying to capture photos directly using the camera api, but this is the preview I got:

& this is the image taken after calling takePicture() which is bigger than the preview itself:

(note: I cropped the height of the previous 2 photos to enhance question readability, & kept the width as is)

I'm using this utility method to choose best optimal preview size before starting the camera preview:

public static Camera.Size getBestAspectPreviewSize(int displayOrientation,
                                                   int width,
                                                   int height,
                                                   Camera.Parameters parameters) {
    double targetRatio = (double) width / height;
    Camera.Size optimalSize = null;
    double minDiff = Double.MAX_VALUE;
    if (displayOrientation == 90 || displayOrientation == 270) {
        targetRatio = (double) height / width;
    }
    List<Camera.Size> sizes = parameters.getSupportedPreviewSizes();
    Collections.sort(sizes,
            Collections.reverseOrder(new SizeComparator()));
    for (Camera.Size size : sizes) {
        double ratio = (double) size.width / size.height;
        if (Math.abs(ratio - targetRatio) < minDiff) {
            optimalSize = size;
            minDiff = Math.abs(ratio - targetRatio);
        }
        if (minDiff < 0.0d) {
            break;
        }
    }
    return (optimalSize);
}

& this method to choose a suitable picture size:

public static Camera.Size getBiggestSafePictureSize(Camera.Parameters parameters) {
    Camera.Size result = null;
    long used = Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory();
    long availableMemory = Runtime.getRuntime().maxMemory() - used;
    for (Camera.Size size : parameters.getSupportedPictureSizes()) {
        int newArea = size.width * size.height;
        long neededMemory = newArea * 4 * 4; // newArea * 4 Bytes/pixel * 4 needed copies of the bitmap (for safety :) )
        if (neededMemory > availableMemory)
            continue;
        if (result == null) {
            result = size;
        } else {
            int resultArea = result.width * result.height;
            if (newArea > resultArea) {
                result = size;
            }
        }
    }
    return (result);
}

& this is the camera preview element in the layout:

<FrameLayout
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:id="@+id/cameraPreview"></FrameLayout>

& I'm following the official documentation for creating the camera preview itself

So, how to force the camera preview to show the exact photo that will be taken?

回答1:

Finally I found it :)

according to this answer & I quote:

While the typical camera is a 4:3 aspect ratio, the preview may also be available in 5:3 and 16:9 ratios and this seems to be accomplished by actually extending the horizontal field of view...

So we need to find a preview size & a picture size, both with 4:3 aspect ratio to be able to utilize the full angle of the camera, so I changed my code like this:

public static Camera.Size determineBestPreviewSize(Camera.Parameters parameters) {
    List<Camera.Size> sizes = parameters.getSupportedPreviewSizes();
    return determineBestSize(sizes);
}

public static Camera.Size determineBestPictureSize(Camera.Parameters parameters) {
    List<Camera.Size> sizes = parameters.getSupportedPictureSizes();
    return determineBestSize(sizes);
}

protected static Camera.Size determineBestSize(List<Camera.Size> sizes) {
    Camera.Size bestSize = null;
    long used = Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory();
    long availableMemory = Runtime.getRuntime().maxMemory() - used;
    for (Camera.Size currentSize : sizes) {
        int newArea = currentSize.width * currentSize.height;
        long neededMemory = newArea * 4 * 4; // newArea * 4 Bytes/pixel * 4 needed copies of the bitmap (for safety :) )
        boolean isDesiredRatio = (currentSize.width / 4) == (currentSize.height / 3);
        boolean isBetterSize = (bestSize == null || currentSize.width > bestSize.width);
        boolean isSafe = neededMemory < availableMemory;
        if (isDesiredRatio && isBetterSize && isSafe) {
            bestSize = currentSize;
        }
    }
    if (bestSize == null) {
        return sizes.get(0);
    }
    return bestSize;
}

回答2:

You should run the same loop over the sizes returned by parameters.getSupportedPictureSizes(), and not rely on the default picture size. Furthermore, I would rather look for the best corresponding pair of preview/picture sizes, and let the picture be cropped on the screen if this aspect ratio does not match the aspect ratio of cameraPreview layout.