JPEG artifacts

What are they and how do you spot them. I see this all over this site ppl saying its got JPEG artifacts, and for the life

of me I can't see them.

See this on Wikipedia

http://en.wikipedia.org/wiki/Compression_artifact

Here's a simple test for you, Ronda. Take one of your nice, high-resolution images. Using the image editing software of your choice, downsize it to something like... 600 pixels wide. Then, save it as a JPG. Most applications will ask you, at that point, how aggressive they should be in compressing the image (which makes for a smaller file, in terms of disk space). Sometimes this is a little slider control, sometimes it's a number (with the lower number being LESS compression, and thus better quality), and sometimes it's a just a grade (good, better, best, etc). Don't save over top of your image, save AS... to two new images. One with very little compression, and the other with very aggressive compression. Then open those two resulting images up in whatever way you like. You'll immediately see the difference.

Ok I see it. It was the terminology I guess that was throwing me off. Its the pixels around the edges of things. I suppose the way to avoid this is using a low ISO number and a fast shutter speed as much as you can ? I noticed my pictures had some noise in them and the ISO was set to high for the daylight conditions. Also they looked alittle better when saved by PSP 10 than by DPP I have both programs set to save at high quality but PSP uses RGB color space and DPP is using sRGB, whatever THAT means! Oh jeeeezzzzz I have so much to learn!

You can set DPP to use any other colour space by going "TOOLS > PREFERENCES > COLOR MANAGEMENT".

 

Using a low ISO number and a fast shutter speed won't do anything to reduce JPEG artifacts. A low ISO number will reduce noise provided the scene is bright enough so as not to be underexposed, and a fast shutter speed will reduce blur from either camera shake or subject movement. The whole JPEG artifact thing is purely to do with the compression of the file, and artifacts should be minimal provided the file is not overly compressed. One thing that can cause big degradations in image quality is over-sharpening of the image. This causes nasty looking artifacts to appear.

 

Do you have any photograph that you would be happy to post that you may be having problems with?

Ok Pete thanks, so its all in the compression, thats good to know. I knew over sharpening wasnt good that it caused what I thought was noise, now I know its JPEG artifacts. As a matter of fact I do have one its in my portfolio called Reflections At Canon Beach here http://www.photo.net/photo/7555621&size=md the setting where

Tv(Shutter Speed)

1/640Sec.

Av(Aperture Value)

F4.0

Metering Modes

Centerweighted average metering

Exposure Compensation

0

ISO Speed

1600

Lens

EF24-105mm f/4L IS USM

Focal Length

40.0 mm

White Balance

Auto

AF mode

AI focus AF

 

I blamed the nasty water on the high ISO am I right?

"I knew over sharpening wasnt good that it caused what I thought was noise, now I know its JPEG artifacts."

 

Oversharpening causes halos around edges, which is another kind of artifact. When you see the word artifact on this site, it either refers to sharpening artifacts or JPEG artifacts. It should be pretty clear which, given the context. And while oversharpening will create unnecessary grain/noise, the term "noise" typically refers to high ISO noise.

 

In your example, ISO 1600 was unnecessary. ISO 400 @ 1/160 would have sufficed. Or you could have stopped down for more DOF if needed.

Ok I pulled the file off up and looked at my post processing It looks like the nasty water is due to my sharping in it in DPP, I over sharpened it.

Bryan I agree the 1600 ISO was unnecessary at the time I thought I needed it as the light was low. But after getting

them home to the PC, and looking at them with the blown highlights, I seen that I didn't capture the scene the way I

wanted to! Thats where the over processing them came in. I reprocessed the picture and while its not exactly what I

wanted its better. I didn't sharpen it, I changed the WB setting from Auto to Daylight and brought the exposure down

1 click. (-17 = 1 stop ? ) in DPP. On the meter in the camera view finder I usually have that thing set right in the

middle on the arrow pointing down. I'm sorry I'm so dumb on this stuff, I'm not sure of all the terminology. Well I have

noticed to get some of my pictures to look right (or at least to my taste) or to get the Highlights to turn white agian in

DPP instead of Red I have to take the exposure down to -17 mostly sometimes as far as -33. So that means I have

to actually have that thing sit not quit on the arrow in the middle but one little dot over to the -2 side or farther? I have

the 5D and If I have confused you I'm sorry. I just want to take a decent picture I can hang on my wall or maybe give

as Christmas presents to my poor unsuspecting family members.

Dunno 'bout PSP10, but PSP7 including a JPEG repair tool that was fairly effective at minimizing blocky artifacts and posterizing.

 

There's also jaggies or aliasing, not quite the same as oversharpening or JPEG artifacts, tho' aliasing can be affected by the other two.

Lex I'm not sure I'll look thank you. Thank you all for the tips and responses. I'm a newbie to all this, I started with a Kodak DX7590 and was taking good photos, except for a little bit of noise now and then. I thought if I had a better/bigger camera I could get better/bigger pictures well I did get bigger pictures thats for sure. Dunno about better but I'll keep trying and hopefully I'll get better. Hopefully I don't drive you all nuts with silly questions. I do use the search function, although I have to admit I didn't today with this question, and I probably should have. I just fired off a new post. Anyway thanks for the help.