How To Find Compression Ratio Of Image

Question

No, y'all can not and information technology does not make sense to do so, since in that location is no ubiquitous definition of the JPEG compression level. The actual issue when saving a JPEG with compression level lx in 1 software can differ significantly from what another software produces when set to level threescore.

If you use ImageMagick as suggested by Rolazaro Azeveires, it will indeed print a quality-number, but this number is not based on EXIF data. ImageMagick calculates its own quality-alphabetize based on the number of quantization tables in the image file and this number may once again differ from the quality level y'all actually ready when saving the paradigm.

For instance, if y'all take a structurally simple epitome, the simplest existence a single-coloured tile, and you salvage it at level 100 with a software using a perceived quality index, the software tin save the image essentially lossless with only a minor number of quantization tables. Analyzing the file later with ImageMagick is likely to give you a very low quality level, since ImageMagick only sees a few quantization tables and does non realize that actually only a small number of quantization tables was necessary to save the file at a loftier quality setting.

Here are for example the quality reported past ImageMagick for some different options when saving an prototype from Photoshop:

          Photoshop                 ImageMagick identify -verbose salvage for web q=1/100         Quality: 55 salve for web q=fourscore/100        Quality: 94 relieve for web q=100/100       Quality: 99 save image q=i/12            Quality: 81 save image q=6/12            Quality: 92 relieve image q=12/12           Quality: 99

Every bit you can see, fifty-fifty within 1 software, two unlike functions 'salve image' and 'salve for web and devices' are both using different quality level scales and neither friction match the quality level reported by ImageMagick.

Addition: Since Chris H tries to argue that the quality level as reported past ImageMagick can exist useful in some cases, I will evidence some examples why that is not the case. The merely reasonable fashion to judge the quality of a JPEG file is to look at information technology and not to rely on some magic number procuded by a software tool.

Let'south first look at this JPEG file. Yes, the quality is not exceptionally good, there are some visible artifacts and ImageMagick reports a quality of 62 while the file size is 17.426 bytes:

enter image description here

Let us assume that we have the same image from a different source and for this file, ImageMagick reports a quality of 99 and the file size is 21.470 bytes:

enter image description here