diff between progressive and non-progressive 1

[Extras]

Would appreciate if someone could explain the difference between progressive and non-progressive jpegs?

Thanks!

 

[rpwin]

When you are saving an image (jpg) for use on the web, saving it as a progressive jpg means that it will be downloaded from the web in more than one pass. This increases the image quality.

Ron Winslow

http://www.rpwdesign.dk

A good plan today is better than a perfect plan tomorrow.

 

[Extras]

Thanks!

 

[gollyg]

Does it increase the final image quality? My impression was that it meant that something would appear on the screen quickly (a low quality version) then, when more image data downloads, the image would improve in quality. But it would still be of the same quality as the optimisation settings dictate.

 

[rpwin]

Absolutly correct, I was a bit vague (misleading) wasn't I.

It stands to reason that the the final quality of the image can never be better than the quality that the image was saved as. I should have said that in comparison to non progressive jpg's there is an increased image quality because there is less compression.

And yes, low res - increasing with each pass.

Thx 'gollyg'

Ron Winslow

http://www.rpwdesign.dk

A good plan today is better than a perfect plan tomorrow.

 

[blueark]

I'm not sure if that's correct. As far as I'm aware, the 'progressive' option has nothing to do with the final quality.

Standard baseline saves the image information from top to bottom, and when it's loaded into your browser, that's the way it displays.

Progressive encoding is essentially a series of scans, starting with a very low-quality image that loads very quickly. They progressively improve in quality as more information is loaded (hence the name). When you open it in a browser, you get to see a rough version of the entire image, so users can see something very quickly without having to wait for the whole image to load. When it does load, however, the quality is no better or worse than standard, non-progressive JPEG.

 

[Eggles]

I agree with blueark. The 'progressive' option only affects how the image displays and has nothing to do with the final quality which is the same as a non-progressive.