[NT73]

What happens when we resize is we add another dose of jpeg, as far as I know. (assuming we are saving to jpeg.
What happens then when it is put onto a site either by site direct (image upload), or such as photobucket indirectly?
Does it get another dose of jpeg'ging or more than one dose.?
I mean we all seem to know the photo is degraded but how much.

[Toad]

Good question. I have always assumed that most websites do some light image conversion when they publish a photo - but probably Jules can tell you more...

[Pavel]

My understanding is that if you conform to size requirement/resolution and submit in the sRGB color space, nothing is done to your file (it may be renamed). Am I wrong?

P

[NT73]

I sometimes find that the image comes out lighter/darker or with artifacts, that the original resized version on my desktop does not have.
This came up because a poster on another board seems to have a great deal of OOF shots, and yet on his photobucket site they are all sharp. I just thought he was posting rejects. :/

[Pavel]

NT, there may be an issue with your color management system. I did find similar problem on several occasions when my color management had some flaw and going step by step helped me find it. I would look for a possibility that your post-processing program uses different ICC profile than your viewing program. Microsoft seems to like to reset itself and ignore the ICC profile you set. Also I would embed sRGB color space in your JPEGs, unless you are doing it already.

Artifacts may be a result of converting from from a large, high resolution and 16 bit PSD file to low res (and by definition 8-bit) JPEG. To minimize the issue (and i did encounter it, but no more), I try to do the minimal compression of JPEGs. The size of jpegs seems to vary with the amount of texture and texture/detail-rich landscape can lead to a large files. Artifacts become visible when you try to compress these files down to 200 K or less. Most of my files are around 500 K, but on occasion they can be double or even tripple that. Also artifacts can happen if you are aggressively sharpening small details or if you sharpen agressively several times. I presharpen but rather gently, sometimes sharpen (not too aggressively) parts of the final PSD file and i always resharpen after downsizing to JPEG. I hope that all this helps

Pavel


I am not sure this helps

[Irma]

I used to have problems with the pictures I posted in flickr. They were darker and sharper. I don't have that problem anymore, but I think flickr did something with the way they handle pictures now. I would suggest you post the same picture in two or three different places, and see if you find any difference.

I understand that jpg's degrade every time you open the file in an editing program, even if you don't do anything to the image. It seems that every time you close the image from PS let's say, you compress the image. About this I am not sure.

[NT73]

Pavel ...When I put a pic on a web site/forum, I do all my pp first and then shrink for web and 'save' to my desktop. So I have a same size copy to verify from.
Any changes, happen after I post to forums.
So I am comparing the one immediately before uploading, and the one uploaded to wherever.

I read that somewhere Irma also, but I tend to only PP once if at all. 99.999% of my pics are jpeg's. But I am not talking about a regular happening, just occasionally.

[Pavel]

Sorry NT - I am obviously barking at a wrong tree.
P

[NT73]

Sorry NT - I am obviously barking at a wrong tree.
P

As long as you are only barking at the tree then fine.
Don't be sorry, and thanks for taking the trouble to respond.

[Zig]

When we "shrink" a jpeg down from a larger size, we resample downwards..called "downrezzing". The more information is in the original file, the more integral is the final image. It's a bit like, if I was recording one audio track in 24 bits and another in 16 bits, then downrezzed the 24-bit one(like an "audio-jpeg", if you like) to 16 bit, the downrezzed one would appear to be a bit better than the one done at 16 bit..even though they are both now at 16 bit.
"Uprezzing" is where one attempts to output an image at a resolution higher than it started: the software has then to "guess" or interpolate the missing information, and it generally looks pants if done in Photoshop, though Genuine Fractals does a darn good job.
Now to the point(!):
I believe Pavel is right here. Generally, if one posts a jpeg at the resolution and colour space the host is requiring(and I believe this to be the case with Flickr), it'll appear just as you sent it in..not compressed any further.
That said, some photo hosts out there seem to recompress/resize anyway...many a time I've posted something sharp as a greased weasel on Pbase, at exactly the required resolution, and the results are slightly blurred.
On the sharpening front, depends on the lens and sensor, I've found. With my old 350D, I needed to progressively smart-sharpen judiciously until doing so finally at exactly the resolution I was outputting. Now, if I shoot with the 1Ds II and a decent prime(the 21mm say), I do no sharpening whatsoever until this stage:
Assuming I'm working on a 16-bit tif, I get it down to 780 pixels on the long end; then I add a tad of smart-sharpen, then save as level 8 jpeg(downrez). In fact, until Jules upped our quota, I'd save once at 780(then sharpen as above) for PBase....and also duplicate the 16bit tif, this time downrezzing to 680 pixels before sharpening then jpegging, so as to do another separate one just for Shuttertalk.

[NT73]

That said, some photo hosts out there seem to recompress/resize anyway...many a time I've posted something sharp as a greased weasel on Pbase, at exactly the required resolution, and the results are slightly blurred.

Thats kind of what I was getting at although I don't use a host, unless you count 'tinypic' as one.
Maybe I will have to try and find an example.

I think I understand the rest of your reply.

[Zig]

Yes NT; sorry, I was using "host" in a sloppy way(I don't really know what it means anyway)..just referring to any web placement of one of our finely-crafted images that seems to come out worse than we created it after we've uploaded it.