An image format that has the least deterioration and the file size can be reduced is found out

ByTrey Ratcliff

What is the image format that has the least deterioration and the file size can be reduced,FirefoxYaThunderbirdFamiliarMozillaWhen compared and verified, it turned out that there is one best image format in all the verification results. As of October 2013, which one is the strongest image format?

Lossy Compressed Image Formats Study (October 2013)
http://people.mozilla.org/~josh/lossy_compressed_image_study_october_2013/

It has been used as a standard for image files on the web for many years "JPEGMore than 20 years passed since the birth. Since the appearance of JPEG, a newImage formatHas been developed with the goal of realizing a file of comparable quality with a smaller size using JPEG as a target, but there is still much debate as to which format is most excellent. Mozilla compared and examined superiority and inferiority of such image format by demonstration experiment.

Mozilla, among various image formats, is frequently discussed as a successor to JPEG "JPEG XR","WebP"AndH.265The still-image (still image) profile of "HEVC-MSPBy comparing it with JPEG which is the standard format, we decided the superiority or inferiority.

In determining the superiority or inferiority of the image format, various indices such as absolute image quality, amount of information that can be added, decoding time, etc. can be considered, but Mozilla providing Firefox, a web browser, Since there is an interest in the file size that gives the biggest influence, how much file size can be reduced when maintaining equivalent qualityCompression ratioMainly I compared the image format.

As we can not judge superiority and inferiority of image quality with the human visual sense, three kinds of experimentsSSIMCompress the source image file using the four quality evaluation algorithms (Y - SSIM, RGB - SSIM, IW - SSIM) and PSNR - HVSMDCT, compare the image quality - compression ratio (file size) based on JPEG It was done.

Algorithm Details look like this.

· Y-SSIM
"The SSIM Index for Image Quality AssessmentIn "Luminance"Evaluating with focus on.
· RGB-SSIM
"The SSIM Index for Image Quality AssessmentIn "RGB"Evaluating with focus on.
· IW-SSIM
"Information Content Weighted Structural Similarity Index for Image Quality AssessmentIn "focus" on the "luminance" to evaluate.
· PSNR-HVS-M
An algorithm to examine the ratio of peak signal and noise, and contrast sensitivity function (CSF) andContrast coefficient based on DCT basis functionEvaluating taking into account.

To ensure the fairness of the evaluation, the following three source images were used for the experiment.

· Lenna(512 × 512 PNG file)


·Kodak24 PNG files provided by

True Color Kodak Images
http://r0k.us/graphics/kodak/


·Tecnick100 PNG files provided by

TESTIMAGES
http://www.tecnick.com/public/code/cp_dpage.php?aiocp_dp=testimages


In addition, software to be used for experiments was carefully selected ones that were easily available on the web, and free software was used for all software except MATLAB, the only charged software. This means that everyone can verify that the experiment is correct this time.

Experimental results of comparison for each compression algorithm are as follows.

◆ 1: Y-SSIM
A quality graph when three kinds of source files are encoded and compressed by the Y - SSIM algorithm. The horizontal axis represents the image quality, and the lower the plot is, the higher the compression (the file size is small) as the vertical axis shows the size (compression ratio) for each file format when JPEG is 1, It can be said.

This is Lenna's graph. JPEG XR (red), which is supposed to be the successor format, results in a larger file size than JPEG (blue) for all images and all image qualities.


Kodak.


Tecnick. Among all three, HEVC - MSP (purple) shows the best performance.



◆ 2: RGB-SSIM
Graph when three kinds of source files are encoded by RGB-SSIM algorithm. Again the graph is higher quality.

Lenna. Both image formats are better than JPEG.


Kodak.


Tecnick. After all HEVC - MSP is excellent.


◆ 3: IW-SSIM
Graph when three types of source files are encoded by IW-SSIM algorithm.

Lenna. Again JPEG XR is a tough result.


Kodak.


Tecnick. HEVC - MSP also has excellent results here.


◆ 4: PSNR-HVS-M
Finally, PSNR-HVS-M is a graph when three types of source files are encoded.

Lenna. The high quality of surprising JPEG is seen.


Kodak.


Tecknic. In general, JPEG is excellent at high image quality, but in the other three image formats, HEVC - MSP is still the most excellent.


As mentioned above, Mozilla's survey results revealed that HEVC-MSP is the most excellent. When considering compression ratio emphasis, HEVC - MSP seems to lead one step in conflict over post JPEG.