![]() Some execution speed savings are therefore expected. The execution time of Dissimilar also includes startup of a new JRE, an SSIM calculation and saving an SSIM “heatmap” image to identify the low values. #Exiftool java codeThis is a good result as the code is currently unoptimised. Results on a homogenous dataset of 1000 greyscale image files showed that ImageMagick took about half the execution time of Dissimilar. For more about that see our iPres paper in September. It is worth noting that there is no built-in support for JPEG2000 files in Apache-Commons Imaging, and it is worth using a known decoder to decompress to tiff for comparison. The original tiff and second tiff were then compared using each tool, each tool therefore having identical inputs. A tiff was migrated to lossy jp2 and then back to tiff. Testing was performed using our Hadoop cluster to enable comparison of results from ImageMagick (PSNR) and Dissimilar (PSNR/SSIM). ![]() Or using variance would enable identification of images where there were large differences in the individual SSIM windows, but where those values might still produce a mean that is assessed as ok. #Exiftool java windowsFor example, setting a minimum value would ensure that the quality of all 8×8 windows stayed above a certain threshold. It may be useful to use a combination of some of the mean, minimum and variance to set a better threshold for image format migration. In addition to the (mean) SSIM value, Dissimilar reports the minimum SSIM value alongside the variance in SSIM values. The SSIM is calculated for an image by splitting it in to 8 pixel by 8 pixel “windows” and then calculating the mean of the results for each window. The result is about 600 lines of commented, pure-Java code for performing image quality analysis. Those experiments showed that, while possible, it was not ideal a large native-code shared object needed to be packaged with the tool and some inline memory management was required.įor Dissimilar I subsequently implemented PSNR and SSIM algorithms from scratch in Java, making use of Apache-Commons Imaging and Math3 libraries. I had previously prototyped a tool that used the OpenCV libraries in Java to perform image comparisons. ![]() I created a prototype tool/library for image quality analysis, called Dissimilar. I wanted to investigate implementation of image comparison algorithms so began investigating. Various tools can be used such as ImageMagick or Matchbox, but they only provide one metric or are for different use-cases. An important part of image file format migration is quality assurance. ![]()
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