问题描述

保存.tiff图像格式时如何保证与原图像属性相同？

解决方案

与图像格式无关，在调用OpenCV库imwrite()函数时，可以在第3位可缺省标志位设置输出图像的参数。函数imwrite()的官方注释如下：

def imwrite(filename, img, params=None): # real signature unknown; restored from __doc__"""imwrite(filename, img[, params]) -> retval.   @brief Saves an image to a specified file..   .   The function imwrite saves the image to the specified file. The image format is chosen based on the.   filename extension (see cv::imread for the list of extensions). In general, only 8-bit.   single-channel or 3-channel (with 'BGR' channel order) images.   can be saved using this function, with these exceptions:.   .   - 16-bit unsigned (CV_16U) images can be saved in the case of PNG, JPEG 2000, and TIFF formats.   - 32-bit float (CV_32F) images can be saved in PFM, TIFF, OpenEXR, and Radiance HDR formats;.     3-channel (CV_32FC3) TIFF images will be saved using the LogLuv high dynamic range encoding.     (4 bytes per pixel).   - PNG images with an alpha channel can be saved using this function. To do this, create.   8-bit (or 16-bit) 4-channel image BGRA, where the alpha channel goes last. Fully transparent pixels.   should have alpha set to 0, fully opaque pixels should have alpha set to 255/65535 (see the code sample below)..   - Multiple images (vector of Mat) can be saved in TIFF format (see the code sample below)..   .   If the format, depth or channel order is different, use.   Mat::convertTo and cv::cvtColor to convert it before saving. Or, use the universal FileStorage I/O.   functions to save the image to XML or YAML format..   .   The sample below shows how to create a BGRA image, how to set custom compression parameters and save it to a PNG file..   It also demonstrates how to save multiple images in a TIFF file:.   @include snippets/imgcodecs_imwrite.cpp.   @param filename Name of the file..   @param img (Mat or vector of Mat) Image or Images to be saved..   @param params Format-specific parameters encoded as pairs (paramId_1, paramValue_1, paramId_2, paramValue_2, ... .) see cv::ImwriteFlags"""

根据官方解释，此函数按照所给参数保存图像img到相应位置filename。需要注意的一点是输出图像的格式是基于所给文件的扩展名。可以保存8bit单通道图像，3通道图像以及16bit，32bit，3通道.tiff图像。最后的标志位针对不同图像类型可以有很多选择，见OpenCV官方注释: imwirte()注释。

在笔者项目中需要保存张7168x7168的单通道.tiff图像，图像原始属性如下：

有关保存.tiff图像的标志位可选如下：

IMWRITE_TIFF_RESUNIT Python: cv.IMWRITE_TIFF_RESUNIT	For TIFF, use to specify which DPI resolution unit to set; see libtiff documentation for valid values.
IMWRITE_TIFF_XDPI Python: cv.IMWRITE_TIFF_XDPI	For TIFF, use to specify the X direction DPI.
IMWRITE_TIFF_YDPI Python: cv.IMWRITE_TIFF_YDPI	For TIFF, use to specify the Y direction DPI.
IMWRITE_TIFF_COMPRESSION Python: cv.IMWRITE_TIFF_COMPRESSION	For TIFF, use to specify the image compression scheme. See libtiff for integer constants corresponding to compression formats. Note, for images whose depth is CV_32F, only libtiff's SGILOG compression scheme is used. For other supported depths, the compression scheme can be specified by this flag; LZW compression is the default.

实现代码如下：

cv.imwrite("D:/Project/images/test.tiff", test_img, ((int(cv.IMWRITE_TIFF_RESUNIT), 2,int(cv.IMWRITE_TIFF_COMPRESSION), 1,int(cv.IMWRITE_TIFF_XDPI), 100,int(cv.IMWRITE_TIFF_YDPI), 100)))

这里要注意，如何实现标志位多参数，这里将参数名称与参数值使用“()”放在一起作为第3位参数，中间使用“，”隔开。IMWRITE_TIFF_RESUNIT表示分辨率单位，这里赋值为“2”表示使用单位“英寸”；IMWRITE_TIFF_COMPRESSION表示图像压缩，参照..\OpenCV4.4.0\opencv\sources\3rdparty\libtiff\tiff.h的定义，此参数有如下预定义值可供选择：

#define      COMPRESSION_NONE        1   /* dump mode */
#define     COMPRESSION_CCITTRLE    2   /* CCITT modified Huffman RLE */
#define     COMPRESSION_CCITTFAX3   3   /* CCITT Group 3 fax encoding */
#define     COMPRESSION_CCITT_T4        3       /* CCITT T.4 (TIFF 6 name) */
#define     COMPRESSION_CCITTFAX4   4   /* CCITT Group 4 fax encoding */
#define     COMPRESSION_CCITT_T6        4       /* CCITT T.6 (TIFF 6 name) */
#define     COMPRESSION_LZW     5       /* Lempel-Ziv  & Welch */
#define     COMPRESSION_OJPEG       6   /* !6.0 JPEG */
#define     COMPRESSION_JPEG        7   /* %JPEG DCT compression */
#define     COMPRESSION_T85         9   /* !TIFF/FX T.85 JBIG compression */
#define     COMPRESSION_T43         10  /* !TIFF/FX T.43 colour by layered JBIG compression */
#define     COMPRESSION_NEXT        32766   /* NeXT 2-bit RLE */
#define     COMPRESSION_CCITTRLEW   32771   /* #1 w/ word alignment */
#define     COMPRESSION_PACKBITS    32773   /* Macintosh RLE */
#define     COMPRESSION_THUNDERSCAN 32809   /* ThunderScan RLE */
/* codes 32895-32898 are reserved for ANSI IT8 TIFF/IT <dkelly@apago.com) */
#define     COMPRESSION_IT8CTPAD    32895   /* IT8 CT w/padding */
#define     COMPRESSION_IT8LW       32896   /* IT8 Linework RLE */
#define     COMPRESSION_IT8MP       32897   /* IT8 Monochrome picture */
#define     COMPRESSION_IT8BL       32898   /* IT8 Binary line art */
/* compression codes 32908-32911 are reserved for Pixar */
#define     COMPRESSION_PIXARFILM   32908   /* Pixar companded 10bit LZW */
#define     COMPRESSION_PIXARLOG    32909   /* Pixar companded 11bit ZIP */
#define     COMPRESSION_DEFLATE     32946   /* Deflate compression */
#define     COMPRESSION_ADOBE_DEFLATE   8       /* Deflate compression,as recognized by Adobe */
/* compression code 32947 is reserved for Oceana Matrix <dev@oceana.com> */
#define     COMPRESSION_DCS             32947   /* Kodak DCS encoding */
#define     COMPRESSION_JBIG        34661   /* ISO JBIG */
#define     COMPRESSION_SGILOG      34676   /* SGI Log Luminance RLE */
#define     COMPRESSION_SGILOG24    34677   /* SGI Log 24-bit packed */
#define     COMPRESSION_JP2000          34712   /* Leadtools JPEG2000 */
#define     COMPRESSION_LERC            34887   /* ESRI Lerc codec: https://github.com/Esri/lerc */
/* compression codes 34887-34889 are reserved for ESRI */
#define     COMPRESSION_LZMA        34925   /* LZMA2 */
#define     COMPRESSION_ZSTD        50000   /* ZSTD: WARNING not registered in Adobe-maintained registry */
#define     COMPRESSION_WEBP        50001   /* WEBP: WARNING not registered in Adobe-maintained registry */

这里选择不压缩，也就是选择1。

IMWRITE_TIFF_XDPI 和 IMWRITE_TIFF_YDPI 选择目标值100即可。

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使用基于phython的OpenCV库imwrite()保存tiff格式图像

问题描述

解决方案

使用基于phython的OpenCV库imwrite()保存tiff格式图像相关推荐

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