【发布时间】：2018-08-19 16:57:54
【问题描述】：
有没有办法将位图压缩到特定的字节大小？例如，1.5MB。问题是到目前为止我看到的所有示例都是调整宽度和高度，但我的要求是调整字节大小。那可能吗？ 另外，压缩位图最直接和正确的方法是什么？我对这个话题很陌生，想从一开始就朝着正确的方向发展。
【问题讨论】：
标签： java android kotlin android-bitmap bitmapfactory
【发布时间】：2018-08-19 16:57:54
【问题描述】：
这是我创建的一个助手类。这会按宽度/高度然后按最大文件大小压缩位图。将图像缩小到 1.5mb 并不是一门精确的科学，但如果图像大于所需的大小，它会使用 jpeg 压缩位图并将质量降低 80%。一旦文件大小小于要求的大小，它将以字节数组的形式返回位图。
public static byte[] getCompressedBitmapData(Bitmap bitmap, int maxFileSize, int maxDimensions) {
Bitmap resizedBitmap;
if (bitmap.getWidth() > maxDimensions || bitmap.getHeight() > maxDimensions) {
resizedBitmap = getResizedBitmap(bitmap,
maxDimensions);
} else {
resizedBitmap = bitmap;
}
byte[] bitmapData = getByteArray(resizedBitmap);
while (bitmapData.length > maxFileSize) {
bitmapData = getByteArray(resizedBitmap);
}
return bitmapData;
}
public static Bitmap getResizedBitmap(Bitmap image, int maxSize) {
int width = image.getWidth();
int height = image.getHeight();
float bitmapRatio = (float) width / (float) height;
if (bitmapRatio > 1) {
width = maxSize;
height = (int) (width / bitmapRatio);
} else {
height = maxSize;
width = (int) (height * bitmapRatio);
}
return Bitmap.createScaledBitmap(image,
width,
height,
true);
}
private static byte[] getByteArray(Bitmap bitmap) {
ByteArrayOutputStream bos = new ByteArrayOutputStream();
bitmap.compress(Bitmap.CompressFormat.JPEG,
80,
bos);
return bos.toByteArray();
}
【讨论】：
-
通过编码到JPEG和随后的解码来降低质量是否真的会减少位图的内存占用？我不明白它是如何工作的，因为在之前和之后每种颜色的像素和字节数相同，不是吗？
-
所以不是吗？我仍然对编码和解码的效果感到困惑。
-
@tim.paetz 非常感谢您的努力，我的截止日期真的很紧，我实现的东西非常简单。但是我稍后会看你的代码，因为这是非常重要的话题
您可以通过以下方式轻松计算位图的大小
width * height * bytes per pixel = size
bytes per pixel 由您的颜色模型定义，例如 RGBA_F16 是 8 个字节，而 ARGB_8888 是 4 个字节，依此类推。有了这个，您应该能够确定您想要的图像的宽度和高度以及颜色编码。
有关位值，请参阅https://developer.android.com/reference/android/graphics/Bitmap.Config。
有关位图内存管理的更多信息，请参阅https://developer.android.com/topic/performance/graphics/manage-memory。
【讨论】：
这对我有用。 将原始位图的区域缩放到 50% 并压缩位图直到其大小
import android.graphics.Bitmap
import android.graphics.BitmapFactory
import android.graphics.Matrix
import android.os.Environment
import android.support.media.ExifInterface //28.0.0
companion object {
const val TAG = "MainActivity"
internal val ROOT_FOLDER_CACHE_IMAGE =
Environment.getExternalStorageDirectory().toString() + "/com.test/cache"
const val _200KB = 200 * 1024
}
private fun displayBitmapAfterCompressing() {
val filePath = Environment.getExternalStorageDirectory().toString() + "/DCIM/Camera/test.jpg"
//ImageView shows bitmap before compressing
var inputStream = FileInputStream(filePath)
original_image_view.setImageBitmap(BitmapFactory.decodeStream(inputStream))
inputStream.close()
//ImageView shows bitmap after compressing
val newFilePath = resizeAndCompressFile(filePath)
if (newFilePath != null) {
inputStream = FileInputStream(newFilePath)
compress_image_view.setImageBitmap(BitmapFactory.decodeStream(inputStream))
inputStream.close()
}
}
private fun resizeAndCompressFile(filePath: String): String? {
val imageFile = File(filePath)
if (imageFile.exists()) {
val fileSize = imageFile.length()
if (fileSize > 0) {
return if (fileSize < _200KB) {
filePath
} else {
resizeAndCompressBitmapTo200KB(filePath)
}
}
}
return null
}
private fun resizeAndCompressBitmapTo200KB(filePath: String): String? {
val imageFile = File(filePath)
val fileSize = imageFile.length()
Log.d(TAG, "size of original file = $fileSize")
if (fileSize > _200KB) {
var qualityCompress = 80
if (fileSize > 3145728) {// > 3MB
qualityCompress = 55
} else if (fileSize > 2097152) {// > 2MB
qualityCompress = 60
} else if (fileSize > 1560576) {// > 1.5MB
qualityCompress = 65
} else if (fileSize > 1048576) {// > 1MB
qualityCompress = 70
}
var newFilePath: String?
do {
newFilePath = compressFileAndReturnNewPathOfNewFile(filePath, qualityCompress)
qualityCompress -= 5
//TODO test
newFilePath?.let {
Log.d(
TAG,
"qualityCompress = " + qualityCompress + "size of new file = " + File(newFilePath).length()
)
}
} while (newFilePath != null && File(newFilePath).length() > _200KB)
//copy attributes from old exif to new exif
if (newFilePath != null) {
copyExif(filePath, newFilePath)
}
return newFilePath
}
return filePath
}
private fun compressFileAndReturnNewPathOfNewFile(filePath: String, qualityCompress: Int): String? {
try {
val inputStream = FileInputStream(filePath)
var compressBitmap = BitmapFactory.decodeStream(inputStream)
//original width height
val widthOriginal = compressBitmap.width
val heightOriginal = compressBitmap.height
//resize image 50% (keep original scale)
val width50Percent: Int = (widthOriginal / 1.41421356237).toInt()
val height50Percent: Int = (heightOriginal / 1.41421356237).toInt()
//
val scaleWidth: Float = width50Percent.toFloat() / widthOriginal
val scaleHeight: Float = height50Percent.toFloat() / heightOriginal
//
//Must Rotate bitmap before upload them
val matrix = Matrix()
matrix.setRotate(getOrientation(filePath).toFloat())
matrix.postScale(scaleWidth, scaleHeight);
compressBitmap = Bitmap.createBitmap(
compressBitmap, 0, 0, compressBitmap.width,
compressBitmap.height, matrix, true
)
//make a new file directory inside the "sdcard" folder
val mediaStorageDir = File(ROOT_FOLDER_CACHE_IMAGE)
if (!mediaStorageDir.exists()) {
mediaStorageDir.mkdirs()
}
var file = File(mediaStorageDir.absolutePath, "compress_image.jpeg")
if (file.exists()) {
file.deleteOnExit()
file = File(mediaStorageDir.absolutePath, "compress_image.jpeg")
}
val fos = FileOutputStream(file)
compressBitmap.compress(Bitmap.CompressFormat.JPEG, qualityCompress, fos)
fos.flush()
fos.close()
inputStream.close()
compressBitmap.recycle()
compressBitmap = null
// Use this for reading the data.
/*val inputStream = FileInputStream(file.absolutePath)
val buffer = ByteArray(file.length().toInt())
inputStream.read(buffer)
inputStream.close()
return buffer*/
return file.absolutePath
} catch (e1: FileNotFoundException) {
Log.e(TAG, "compressFileToByteArray(1)", e1)
} catch (e2: IOException) {
Log.e(TAG, "compressFileToByteArray(2)", e2)
} catch (e3: Exception) {
Log.e(TAG, "compressFileToByteArray(3)", e3)
}
return null
}
private fun copyExif(oldPath: String, newPath: String) {
val attributes = arrayOf(
ExifInterface.TAG_IMAGE_WIDTH,
ExifInterface.TAG_IMAGE_LENGTH,
ExifInterface.TAG_BITS_PER_SAMPLE,
ExifInterface.TAG_COMPRESSION,
ExifInterface.TAG_PHOTOMETRIC_INTERPRETATION,
ExifInterface.TAG_ORIENTATION,
ExifInterface.TAG_SAMPLES_PER_PIXEL,
ExifInterface.TAG_PLANAR_CONFIGURATION,
ExifInterface.TAG_Y_CB_CR_SUB_SAMPLING,
ExifInterface.TAG_Y_CB_CR_POSITIONING,
ExifInterface.TAG_X_RESOLUTION,
ExifInterface.TAG_Y_RESOLUTION,
ExifInterface.TAG_RESOLUTION_UNIT,
ExifInterface.TAG_STRIP_OFFSETS,
ExifInterface.TAG_ROWS_PER_STRIP,
ExifInterface.TAG_STRIP_BYTE_COUNTS,
ExifInterface.TAG_JPEG_INTERCHANGE_FORMAT,
ExifInterface.TAG_JPEG_INTERCHANGE_FORMAT_LENGTH,
ExifInterface.TAG_TRANSFER_FUNCTION,
ExifInterface.TAG_WHITE_POINT,
ExifInterface.TAG_PRIMARY_CHROMATICITIES,
ExifInterface.TAG_Y_CB_CR_COEFFICIENTS,
ExifInterface.TAG_REFERENCE_BLACK_WHITE,
ExifInterface.TAG_DATETIME,
ExifInterface.TAG_IMAGE_DESCRIPTION,
ExifInterface.TAG_MAKE,
ExifInterface.TAG_MODEL,
ExifInterface.TAG_SOFTWARE,
ExifInterface.TAG_ARTIST,
ExifInterface.TAG_COPYRIGHT,
ExifInterface.TAG_EXIF_VERSION,
ExifInterface.TAG_FLASHPIX_VERSION,
ExifInterface.TAG_COLOR_SPACE,
ExifInterface.TAG_GAMMA,
ExifInterface.TAG_PIXEL_X_DIMENSION,
ExifInterface.TAG_PIXEL_Y_DIMENSION,
ExifInterface.TAG_COMPONENTS_CONFIGURATION,
ExifInterface.TAG_COMPRESSED_BITS_PER_PIXEL,
ExifInterface.TAG_MAKER_NOTE,
ExifInterface.TAG_USER_COMMENT,
ExifInterface.TAG_RELATED_SOUND_FILE,
ExifInterface.TAG_DATETIME_ORIGINAL,
ExifInterface.TAG_DATETIME_DIGITIZED,
ExifInterface.TAG_SUBSEC_TIME,
ExifInterface.TAG_SUBSEC_TIME_ORIGINAL,
ExifInterface.TAG_SUBSEC_TIME_DIGITIZED,
ExifInterface.TAG_EXPOSURE_TIME,
ExifInterface.TAG_F_NUMBER,
ExifInterface.TAG_EXPOSURE_PROGRAM,
ExifInterface.TAG_SPECTRAL_SENSITIVITY,
ExifInterface.TAG_PHOTOGRAPHIC_SENSITIVITY,
ExifInterface.TAG_OECF,
ExifInterface.TAG_SENSITIVITY_TYPE,
ExifInterface.TAG_STANDARD_OUTPUT_SENSITIVITY,
ExifInterface.TAG_RECOMMENDED_EXPOSURE_INDEX,
ExifInterface.TAG_ISO_SPEED,
ExifInterface.TAG_ISO_SPEED_LATITUDE_YYY,
ExifInterface.TAG_ISO_SPEED_LATITUDE_ZZZ,
ExifInterface.TAG_SHUTTER_SPEED_VALUE,
ExifInterface.TAG_APERTURE_VALUE,
ExifInterface.TAG_BRIGHTNESS_VALUE,
ExifInterface.TAG_EXPOSURE_BIAS_VALUE,
ExifInterface.TAG_MAX_APERTURE_VALUE,
ExifInterface.TAG_SUBJECT_DISTANCE,
ExifInterface.TAG_METERING_MODE,
ExifInterface.TAG_LIGHT_SOURCE,
ExifInterface.TAG_FLASH,
ExifInterface.TAG_SUBJECT_AREA,
ExifInterface.TAG_FOCAL_LENGTH,
ExifInterface.TAG_FLASH_ENERGY,
ExifInterface.TAG_SPATIAL_FREQUENCY_RESPONSE,
ExifInterface.TAG_FOCAL_PLANE_X_RESOLUTION,
ExifInterface.TAG_FOCAL_PLANE_Y_RESOLUTION,
ExifInterface.TAG_FOCAL_PLANE_RESOLUTION_UNIT,
ExifInterface.TAG_SUBJECT_LOCATION,
ExifInterface.TAG_EXPOSURE_INDEX,
ExifInterface.TAG_SENSING_METHOD,
ExifInterface.TAG_FILE_SOURCE,
ExifInterface.TAG_SCENE_TYPE,
ExifInterface.TAG_CFA_PATTERN,
ExifInterface.TAG_CUSTOM_RENDERED,
ExifInterface.TAG_EXPOSURE_MODE,
ExifInterface.TAG_WHITE_BALANCE,
ExifInterface.TAG_DIGITAL_ZOOM_RATIO,
ExifInterface.TAG_FOCAL_LENGTH_IN_35MM_FILM,
ExifInterface.TAG_SCENE_CAPTURE_TYPE,
ExifInterface.TAG_GAIN_CONTROL,
ExifInterface.TAG_CONTRAST,
ExifInterface.TAG_SATURATION,
ExifInterface.TAG_SHARPNESS,
ExifInterface.TAG_DEVICE_SETTING_DESCRIPTION,
ExifInterface.TAG_SUBJECT_DISTANCE_RANGE,
ExifInterface.TAG_IMAGE_UNIQUE_ID,
ExifInterface.TAG_CAMARA_OWNER_NAME,
ExifInterface.TAG_BODY_SERIAL_NUMBER,
ExifInterface.TAG_LENS_SPECIFICATION,
ExifInterface.TAG_LENS_MAKE,
ExifInterface.TAG_LENS_MODEL,
ExifInterface.TAG_LENS_SERIAL_NUMBER,
ExifInterface.TAG_GPS_VERSION_ID,
ExifInterface.TAG_GPS_LATITUDE_REF,
ExifInterface.TAG_GPS_LATITUDE,
ExifInterface.TAG_GPS_LONGITUDE_REF,
ExifInterface.TAG_GPS_LONGITUDE,
ExifInterface.TAG_GPS_ALTITUDE_REF,
ExifInterface.TAG_GPS_ALTITUDE,
ExifInterface.TAG_GPS_TIMESTAMP,
ExifInterface.TAG_GPS_SATELLITES,
ExifInterface.TAG_GPS_STATUS,
ExifInterface.TAG_GPS_MEASURE_MODE,
ExifInterface.TAG_GPS_DOP,
ExifInterface.TAG_GPS_SPEED_REF,
ExifInterface.TAG_GPS_SPEED,
ExifInterface.TAG_GPS_TRACK_REF,
ExifInterface.TAG_GPS_TRACK,
ExifInterface.TAG_GPS_IMG_DIRECTION_REF,
ExifInterface.TAG_GPS_IMG_DIRECTION,
ExifInterface.TAG_GPS_MAP_DATUM,
ExifInterface.TAG_GPS_DEST_LATITUDE_REF,
ExifInterface.TAG_GPS_DEST_LATITUDE,
ExifInterface.TAG_GPS_DEST_LONGITUDE_REF,
ExifInterface.TAG_GPS_DEST_LONGITUDE,
ExifInterface.TAG_GPS_DEST_BEARING_REF,
ExifInterface.TAG_GPS_DEST_BEARING,
ExifInterface.TAG_GPS_DEST_DISTANCE_REF,
ExifInterface.TAG_GPS_DEST_DISTANCE,
ExifInterface.TAG_GPS_PROCESSING_METHOD,
ExifInterface.TAG_GPS_AREA_INFORMATION,
ExifInterface.TAG_GPS_DATESTAMP,
ExifInterface.TAG_GPS_DIFFERENTIAL,
ExifInterface.TAG_GPS_H_POSITIONING_ERROR,
ExifInterface.TAG_INTEROPERABILITY_INDEX,
ExifInterface.TAG_THUMBNAIL_IMAGE_LENGTH,
ExifInterface.TAG_THUMBNAIL_IMAGE_WIDTH,
ExifInterface.TAG_DNG_VERSION,
ExifInterface.TAG_DEFAULT_CROP_SIZE,
ExifInterface.TAG_ORF_THUMBNAIL_IMAGE,
ExifInterface.TAG_ORF_PREVIEW_IMAGE_START,
ExifInterface.TAG_ORF_PREVIEW_IMAGE_LENGTH,
ExifInterface.TAG_ORF_ASPECT_FRAME,
ExifInterface.TAG_RW2_SENSOR_BOTTOM_BORDER,
ExifInterface.TAG_RW2_SENSOR_LEFT_BORDER,
ExifInterface.TAG_RW2_SENSOR_RIGHT_BORDER,
ExifInterface.TAG_RW2_SENSOR_TOP_BORDER,
ExifInterface.TAG_RW2_ISO,
ExifInterface.TAG_RW2_JPG_FROM_RAW,
ExifInterface.TAG_NEW_SUBFILE_TYPE,
ExifInterface.TAG_SUBFILE_TYPE
/*
There are private attributes
ExifInterface.TAG_EXIF_IFD_POINTER,
ExifInterface.TAG_GPS_INFO_IFD_POINTER,
ExifInterface.TAG_INTEROPERABILITY_IFD_POINTER,
ExifInterface.TAG_SUB_IFD_POINTER,
ExifInterface.TAG_ORF_CAMERA_SETTINGS_IFD_POINTER,
ExifInterface.TAG_ORF_IMAGE_PROCESSING_IFD_POINTER,
ExifInterface.TAG_HAS_THUMBNAIL,
ExifInterface.TAG_THUMBNAIL_LENGTH,
ExifInterface.TAG_THUMBNAIL_DATA*/
)
val oldExif = ExifInterface(oldPath)
val newExif = ExifInterface(newPath)
attributes.forEach { attribute ->
oldExif.getAttribute(attribute)?.let { value ->
newExif.setAttribute(attribute, value)
}
}
newExif.saveAttributes()
}
/**
* Get orientation of bitmap.
*
* @param filePath : link of bitmap in sdcard
* @return Orientation of bitmap
*/
private fun getOrientation(filePath: String?): Int {
var ori = 0
if (filePath != null) {
val exif: ExifInterface
try {
if (filePath.contains("file://")) {
exif = ExifInterface(filePath.substring(7))
} else {
exif = ExifInterface(filePath)
}
val exifOrientation = exif.getAttributeInt(
ExifInterface.TAG_ORIENTATION,
ExifInterface.ORIENTATION_NORMAL
)
when (exifOrientation) {
ExifInterface.ORIENTATION_UNDEFINED -> {
}
ExifInterface.ORIENTATION_NORMAL -> {
}
ExifInterface.ORIENTATION_ROTATE_180 -> ori = 180
ExifInterface.ORIENTATION_ROTATE_90 -> ori = 90
ExifInterface.ORIENTATION_ROTATE_270 -> ori = 270
else -> {
}
}
} catch (e: IOException) {
Log.e(TAG, "getOrientation(String filePath) method: ", e)
}
}
return ori
}
【讨论】：
请参阅我的答案（不使用 while 循环）： How to reduce image size into 1MB
如果您当前传递的位图采用 ARGB_8888 配置（因此每个像素 4 个字节。当它不是 ARGB_8888 时，您可以使用以下方法将其转换为该位图：
/**
* Convert a Bitmap to a Bitmap that has 4 bytes per pixel
* @param input The bitmap to convert to a 4 bytes per pixel Bitmap
*
* @return The converted Bitmap. Note: The caller of this method is
* responsible for reycling the input
*/
public static Bitmap to4BytesPerPixelBitmap(@NonNull final Bitmap input){
final Bitmap bitmap = Bitmap.createBitmap(input.width, input.height, Bitmap.Config.ARGB_8888);
// Instantiate the canvas to draw on:
final Canvas canvas = new Canvas(bitmap);
canvas.drawBitmap(input, 0, 0, null);
// Return the new bitmap:
return bitmap;
}
【讨论】：