JPG lossless transformations - is progressive always better?

[Sprintdriver]

Hi.

I've noticed that selecting "Make progressive JPEG file" every time creates smaller files compared to jpg files that is not progressive.
I understand the concept of progressive JPG file (when loading, it starts out blurred and gradually looks sharper).

But I have two questions regarding this:

1. Would there be cases where non-progressive JPG is the better choice?

2. When saving an image using standard save file dialog, will / should I expect that - there might be any visual differences between a progressive and a non-progressive JPG, if all the other settings is equal?


Thanks

[Bhikkhu Pesala]

I have never noticed before, but what you say seems to be true. Progressive JPG images are smaller (about 98% in my test of a large image).

The number of unique colours is identical in both versions, so I guess there is no difference in quality. So I see no disadvantage in using progressive JPG for web images. Smaller is always better for the web.

WebP would be better still, but some browsers cannot view them.

[Sprintdriver]

A little update:

Regarding JPG Progressive versus non-progressive
I tried to load two identical (except one was saved as progressive) JPG's into Gimp, and then compare them (top layer in "Difference" mode). The result was pit black, not even a single pixel deviated from complete black.

Regarding WebP
I have a lot of screenshots of web pages laying around. Most of them is PNG format saved with PNGOUT (and I figure some good setttings that gives smallest possible file size).
Just by coincidence I happend to save one of those as WebP with Lossless options checked. Guess if I was supprised to see that filesize of WebP lays around half the size of identical PNG files - is that really true

If WepP is that much better compared to JPG's, it's just too sad many programs (and other users) just doesn't support it yet.

[HeftCD]

Pro JPEG

hi

webp is a tricky format. Of course it compresses sometimes better than jpeg.
But not allways. :P
And the results are not best in any cases. Sometines the image gets very unsharp.

If you want to save even smaller: Don't save your pictures anymore .... "write" (an image as a program) them into "BPG". (Better portable Graphics).

there is no smaller, while quality stays better. But ... it cost's really, really much CPU, energy and time: To wirte the "code" for ... that one image.
and of course not all programs/ browsers support .bpg without JS. Even irfan does not. So far. ooops! :P


There are many reasons to save as PNG or as GIF aswell as JPEG.
But it depends on the case.

JPEG => Photos
JPEg2000 = lossy or lossless, but often expensive encoder [and costs CPU! + time ]
PNG = full color Screenshots, photos, or artwork (better than TIF)
GIF and PNG for less detail pictures with big areas of same color/ less pattern; bad for photos!!!!
GIF can be smallest for least color <= 256, can be even smaller than png !!

JPEG, PNG and GIF are known by all browsers
webp only in chome; Firefox with addon?; IE = LoOOL!
bpg = all, with javascript on

but... why does irfanview not support this format yet? :P

[Jeremy]

Jpg full name is JPEG. A JPEG image stores a single bitmap in 24-bit color. JPEG is a platform-independent format that supports the highest level of compression, however, this compression is lossy. Asymptotic JPEG files support interlacing. GIF (Graphics Interchange Format) is the original meaning of "image interchange format" is CompuServe company in 1987 to develop the image file format. GIF file data, is based on the LZW algorithm for continuous tone lossless compression format. Its compression rate is generally around 50%, it does not belong to any application. At present almost all related software support it, the public domain has a large number of software in the use of GIF image files.