JPEG Compression??

[flagpole]

Oh right i may be able to shed some light on this. Lossless jpeg is no longer lossless. it's just high quality.

which is ridiculous. look at the two images below. they should both should be the same. one is png, the other 'lossless' jpeg.

they are clearly not the same. the jpeg shows all the signs of lossy, colour bleed, gibbs phenomenon. mediainfo even says it has chroma subsampling.

[flagpole]

and the png

[LindaSue]

Thanks, flagpole. I had no trouble viewing that picture in any program. Looks like it's a problem with earlier versions of PSP then. I wonder if it was fixed in X3 or not until X4.

[LindaSue]

Just to add to the mystery, I copied your PNG example into PSP8 and saved it as a lossless JPG. It looks identical to the PNG file when I reopen it. No bleeding or blurring, etc. So, it would seem that when Corel fixed the lossless JPG format so that it could be read by other programs, they broke it even worse than it was before.

[flagpole]

it's not lossless at all. that's how they've fixed it.

[JStanley]

deleted

[JRosenfeld]

I don't have PSPX4 but the Lossless JPGs created with PSP8 and X2 can't be viewed in anything other than PSP. They must have changed something since X2. JRosenfeld, can you post a sample of one here so that I can see if any of my programs can view it?

[flagpole]

bmp wouldn't be my first choice. But i agree lossless and jpeg do not go together. The question is why they would add the option, or a feature called lossless jpeg when it is not lossless.

[LindaSue]

JRosenfeld, how much compression did you use on the robin? I can see a definite difference between the two images. There are artifacts all the way around the bird that aren't on the lossless one. I had no trouble viewing the lossless one.

I noticed something else different about the lossless JPGs created by PSPX4. They're much smaller than the ones made with X2. I just saved the robin picture with X2 as a lossless JPG and the file size is 500kb. Your lossless one is 178kb and when I saved it as a PNG file it is 375kb.

[JRosenfeld]

JRosenfeld, how much compression did you use on the robin? I can see a definite difference between the two images. There are artifacts all the way around the bird that aren't on the lossless one. I had no trouble viewing the lossless one.

I noticed something else different about the lossless JPGs created by PSPX4. They're much smaller than the ones made with X2. I just saved the robin picture with X2 as a lossless JPG and the file size is 500kb. Your lossless one is 178kb and when I saved it as a PNG file it is 375kb.

I selected progressive encoding, compression factor 20, Chroma subsampling 'YCbCr 1x1 1x1 1x1 (none)' (whatever that means)

[flagpole]

@Linda that's because in X4 it is not lossless. It's just a high quality jpeg. They clearly dropped the lossless and didn't tell anyone.

Chroma sub sampling is a method by which the colour is stored at a lower quality than the brightness. It works well with photos to say have the colour at half the detail of the brightness because the Eye is more sensitive to the latter.

[LindaSue]

JRosenfeld, how much compression did you use on the robin? I can see a definite difference between the two images. There are artifacts all the way around the bird that aren't on the lossless one. I had no trouble viewing the lossless one.

I noticed something else different about the lossless JPGs created by PSPX4. They're much smaller than the ones made with X2. I just saved the robin picture with X2 as a lossless JPG and the file size is 500kb. Your lossless one is 178kb and when I saved it as a PNG file it is 375kb.

I selected progressive encoding, compression factor 20, Chroma subsampling 'YCbCr 1x1 1x1 1x1 (none)' (whatever that means)

That explains all the artifacts and it's not really a fair comparison. I thought the lossless one looked pretty good but maybe they would have looked the same had you only compressed the progressive one to a factor of 1 rather than 20.

[alexhuang888]

bmp wouldn't be my first choice. But i agree lossless and jpeg do not go together. The question is why they would add the option, or a feature called lossless jpeg when it is not lossless.

lossless jpeg is never popular. I believer they do so to make script compatibility. to remove it just another disaster to others. still, it has to say it clear.

[teknisyan]

@LindaSue,

Can you tell me what program do you want to open the lossless jpeg? Because I created a lossless jpeg from a raw file or Nikon D3100 and I can open the photo using MS Paint, Quicktime Picture Viewer, Windows Live Photo Gallery, PhotoShop Element and Windows Photo Viewer.

@flagpole

I have the updated PSP X4 and for some reason the exif data on the photo that I saved above says that it was PSP 14.00.

Since I cannot insert it here... You can download the lossless jpeg that I created here.

[flagpole]

@LindaSue,

Can you tell me what program do you want to open the lossless jpeg? Because I created a lossless jpeg from a raw file or Nikon D3100 and I can open the photo using MS Paint, Quicktime Picture Viewer, Windows Live Photo Gallery, PhotoShop Element and Windows Photo Viewer.

@flagpole

I have the updated PSP X4 and for some reason the exif data on the photo that I saved above says that it was PSP 14.00.

Since I cannot insert it here... You can download the lossless jpeg that I created here.

that image is simply not lossless. it is a very high quality lossy image.

the idea of something being lossless is a binary state, it is lossless or it isn't, nearly lossless, almost lossless, is just lossy.

the images i uploaded at the top of page 2 show the difference, you can see between the lossless png and the 'lossless' jpeg there are clear differences. this would not be the case if they were lossless. with an 14MP photo this difference is obviously more subtle, but then visually you wouldn't be able to distinguish it down to a compression factor of say 10.

this is perhaps further demonstrated by the fact that if you save your 14MP image in the native pspimage format which is lossless the file is 25meg, (the uncompressed image would be 42meg) considerable bigger than the 8meg of your jpeg

there is nothing wrong having the setting 'maximum quality' or similar for jpeg. but that shouldn't be called lossless. it's an important aspect of many people's work flow to save in a lossless format whilst they are working, and only output to a lossy format at the end. you might think the difference is subtle, for photos it obviously is, but for graphics it is far from subtle. in the two examples i posted the difference is obvious. the actual lossless image contains ~400 colours, the 'lossless' jpeg around 4000 and that can never be undone. if that was actual work, that i had saved 'losslessly' to come back to later the whole thing would have been ruined. worse there is a generational effect, if i opened it and worked on it again, the effect would be magnified each time.

in short. the PSP X4 lossless jpeg, is not lossless. the lossless jpeg has been removed presumably for compatibility reasons, it either needs restoring with a warning re compatibility, or 'lossless' jpeg needs renaming to 'maximum quality' or similar.