Jpeg test update

[JZaun]

CoolToolguy asked for a different pic. I chose a colored object with detail. I cannot see any degridation of color of detail after 80 save cycles. Since I would never modify and re-save a image any near 80 times I do not see jpeg re-compression issue being a negative factor im my decision to use raw or jpeg. I do think from other reading, that I should save a raw or tiff image if I think I am going to be changing it over and over!! or if I know in time to change the camera that it is a critical shot. With my skill level in PSE2 that is not going to happen any time soon. Here are 2 more pics, the orriginal and the 80th save.

original


Copy 80



This is part of my ongoing process to decide if I am going to shoot raw or Jpeg..Just FYI, for many reasons, jpeg is ahead but hasn't won as of yet. more reasons why later.

ONE interesting note!!! somewhere between the first copy and copy 20 the image grew in size and the image streatched length wise!

JZaun

JZaun

[Scottes]

Jerry, you must be doing something wrong. Or maybe I am.

I saved your original duck, and created an action
File... Open... 51duck-1-web.jpg
File... Save As...JPG set at quality 12 (the highest)
File... Close

I assigned F2 to the action to make it easy. After 80 runs of the action I got this:



I saw degradation in the ocean after 5 runs, quite clearly. The duck itself is still not too bad, considering the brutality of the test.

[JZaun]

It appears that you are saving as web.. I was saving as xxx to hard drive. Something about resaving web size?? I don't know. I would never resave a web pic anyway only one from my file..?


JZaun

[evilenglishman]

as with the previous example of the screw, the file size of your second image is almost double the size of the original

[Scottes]

This time I "Saved As" Jpg, not Save for Web. Check my Action.

The file size increase is expected. It will happen every time. JPG is a lossy format, and some data will be lost as it changes colors to make it easier to compress. Thus the algorithm runs different every time, and edges are made sharper each time, as can be seen in the ocean in my pic. Since this is a greater variation between pixels the algorithm won't be as efficient, and thus it ends up as a larger file. Every time.

Jerry, where you by chance opening "51duck.jpg" and Saving As "51duck2.jpg" every time? I opened "51duck.jpg" and saved over it as "51duck.jpg" overwriting the original. So I was opening the file I just compressed, and compressing it again.

[JZaun]

I opened duck and saved as "duck1 " the opened and saved as duck 1 over duck 1. overwriting itself. I was dealing with the original pic. You are dealing with the web pic.

JZaun

[nomel]

Why doesn't anyone ever use png? It's lossless, and works great. Support 32 bit color and everything.

[Scottes]

A PM from Jerry:

My pic was resized for the web after being saved 80 times! Thats the difference.. You are resaving the web pic. It is already degridated by being downsized for the web.!

Good point. Yes, I was taking your resized image.

Hold on...

100% Crop from orignal TIFF, Saved as JPG quality 12, ONCE


100% Crop from orignal TIFF, Saved as JPG quality 12, 25 TIMES


Still a big difference.

Now, I resized both for the web, from 500x500 to 200x200



Who can tell? There IS degradation in the resized ones, but the resize algorithm hides it pretty well.

So if all you're going to do is view on the web, then JPG all the time. But if you ever print that original-been-JPGed-20-times image, you'll see a difference.

[Conk]

I'm going to just jump in here and ask,
when you are resaving the photo are you replacing the file or making a new one? You can resave the same file a million times but if you keep saving the file into a new name it will make a copy. Then I'm sure you'll start to see the image degrade.

[Conk]

Originally Posted by nomel

Why doesn't anyone ever use png? It's lossless, and works great. Support 32 bit color and everything.

File size?

[Scottes]

Originally Posted by Conk

File size?

Ha. Space is cheap. It's time

Same 8-bit image saved as JPG and PNG.
JPG: 2 seconds, 2.4 Meg
PNG: 43 seconds, 5.4 meg

Ouch!

[evilenglishman]

Generally people don't use png because of its larger file size.
Most consider png to be an alternative to gif because of its support for transparency.
However the problem is that the most popular browsers don't have built in support for png transparency, they support png - just not the transparency part.
Hence the reason no one uses it (yet).

[slejhamer]

My results are similar to Scottes':

http://www.photography-on-the.net/fo...amp;highlight=

[JZaun]

slejhamer


Your test is run the same way scottes was on his first test. Your original file was only 504X403 and the crop was 432X 355. I ran the test with a full size jpeg file and croped after the last save. I didn't find your file size but scottes second test was more like mine. I can blow any pic out of the water with a crop. Try it using a full size file. I think your results will be more like mine and scottes second test..

JZaun

[slejhamer]

Originally Posted by JZaun

slejhamer

Your test is run the same way scottes was on his first test. Your original file was only 504X403 and the crop was 432X 355. I ran the test with a full size jpeg file and croped after the last save. I didn't find your file size but scottes second test was more like mine. I can blow any pic out of the water with a crop. Try it using a full size file. I think your results will be more like mine and scottes second test..

JZaun

Hi Jerry. You are mistaken, but I should have been more clear in my post. The test was done using a full-size duplicate of the original 6mp image file. Only after the repeated saves did I crop at 100% and resize for the web, so the size of the web posts has no bearing. I can send you the full-size files if you wish (I saved full-size copies of #21 and #81), and you would see exactly the same thing as I have posted, just much bigger!

Besides, Scottes' second test after 25 saves looks much more like mine at 21 saves than it does yours. As he said, there is "still a big difference."

Still, this is something of an academic exercise and your point about JPEG quality is valid. For practical purposes, there is nothing wrong with shooting a JPEG, editing, and then saving it again. I prefer RAW for other reasons (ease of WB and exposure correction) but I save my final image in JPEG format and delete the TIFFs I use for editing. Much of the criticism of JPEG is overstated. 8)

Cheers!

P.S. You don't have the "save as a copy" box checked when the "save as" dialog opens, do you?