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Read and write blocks of blocked image data as JPEG files

Since R2021a


The JPEGBlocks object is an adapter that reads and writes 2-D blocked image data in the JPEG format.

When writing to disk, the object creates an individual JPEG file for each block and saves the image files in a folder. For multiresolution images, the object creates one subfolder for each resolution level. The object also creates and saves a MAT file with information about the blocked image, including the image size, block size, and data type.

The object supports lossy and lossless compression. By default, the object writes JPEG image files with lossy compression and a quality factor of 75. To use lossy compression with a different quality factor, create the object and then change the quality factor using the JPEGQuality property. To use lossless compression, create the object and then specify the CompressionMode property as "Lossless". For example, to specify a quality factor of 90, use this code.

adapter = images.blocked.JPEGBlocks;
adapter.JPEGQuality = 90;

The table lists the support that the JPEGBlocks object has for various blockedImage capabilities.

Data types

This object supports 2-D images only:

  • Binary images of size m-by-n with data type logical

  • Grayscale images of size m-by-n with data type uint8

  • Truecolor (RGB) images of size m-by-n-by-3 with data type uint8

Multiple resolution levelsYes
Process blocks in parallel using the apply functionYes
Resume block processing using the apply functionYes




adapter = images.blocked.JPEGBlocks creates a JPEGBlocks object that reads and writes blocked image data as JPEG files, with one JPEG file for each block.


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JPEG quality factor, specified as a number in the range [0, 100]. Higher numbers specify better quality because there is less image degradation due to compression, but the resulting file size is larger.

JPEG compression mode, specified as the string scalar or character vector "Lossy" or "Lossless". If you specify "Lossless", then the adapter ignores the JPEGQuality property.

Data Types: string | char


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Create a blocked image.

bim = blockedImage('tumor_091R.tif');

Write image data to files. Specify the images.blocked.JPEGBlocks adapter. Choose to write in highest quality. JPG uses lossy compression, so space required is still significantly lower than other formats.

wa = images.blocked.JPEGBlocks();
wa.JPEGQuality = 100;
write(bim, "folderOfJPGs", "Adapter", wa);

Create a blocked image from the folder of images. The blockedImage object automatically picks the appropriate adapter.

bjpeg = blockedImage("folderOfJPGs");
  JPEGBlocks with properties:

        JPEGQuality: 100
    CompressionMode: "Lossy"
        BlockFormat: "jpeg"

Version History

Introduced in R2021a