Support saving screenshot images in JPEG format with compression

[kazurayam]

Selenium's takeScreanshot feature creates image in PNG, it does not create image in JPEG.

I want to take screenshot of web pages, I want the image files to be as small in byte size as possible.

I want to have an option to saven the screenshot in JPEG format, not PNG format.

I want to specify the compression quality. The compression quality could be in the range of (0.1, 1.0].

How to implement the conversion from PNG to JPEG? It is possible using the pure Java8.

https://stackoverflow.com/questions/17108234/setting-jpg-compression-level-with-imageio-in-java

[kazurayam]

I have done a study to see how much effective to support JPEG as screenshot.

Screenshots in PNG and JPEG - a study of file size

File	Quality	Size(bytes)
screenshot.png	1.0	474,873
screenshot-100.jpg	1.0	238,094
screenshot-90.jpg	0.9	96,446
screenshot-80.jpg	0.8	70,615
screenshot-70.jpg	0.7	59,403
screenshot-60.jpg	0.6	52,483
screenshot-50.jpg	0.5	48,098
screenshot-40.jpg	0.4	43,136
screenshot-30.jpg	0.3	38,695
screenshot-20.jpg	0.2	33,197
screenshot-10.jpg	0.1	26,054

The original PNG image is this:

The screenshot-90.jpg is this:

The screenshot-70.jpg is this:

The screenshot-10.jpg is this:

[kazurayam]

It is quite obvious that the takeEntirePageImageAsJpeg() method is useful.

The JPEG image with the compression quality 0.9 looks almost no different from the original PNG, but the file size in bytes is far smaller (almost 20% of the original).

The JPEG images would be sufficient for "Visual Inspection", and the byte size of the archived report can be much reduced.

[kazurayam]

v0.2.1 supports this