Saving images in Photoshop
Discussion
OK simple question for my simple mind...;)
When I save an image in PS and select image quality 12 I get an image somewhere in the region of 5-7MB, if I select image quality 8 it generates disk space friendly 1MBish images..... to my eyes there is no discernable difference.
Now I'm sure there are some very significant differences and certainly whenever I'm asked to provide images for a client or for creating prints I always use the highest quality (having generated the highest quality TIFF I can from RAW). But I'm curious to know what the difference is technically, certainly there's the same amount of icons. Anyone?
When I save an image in PS and select image quality 12 I get an image somewhere in the region of 5-7MB, if I select image quality 8 it generates disk space friendly 1MBish images..... to my eyes there is no discernable difference.
Now I'm sure there are some very significant differences and certainly whenever I'm asked to provide images for a client or for creating prints I always use the highest quality (having generated the highest quality TIFF I can from RAW). But I'm curious to know what the difference is technically, certainly there's the same amount of icons. Anyone?
It's all about compression... JPEG compresses a file, and you lose data each time you re-save (compression on compression) and it's a system whereby you lose them.
In the assumption you're keeping the original RAW file anyway, you may as well go for the size friendly 1MB versions for web use etc.
In the assumption you're keeping the original RAW file anyway, you may as well go for the size friendly 1MB versions for web use etc.
I'll be saving jpegs around the 8 mark in future then. What exactly is it thats compressed though? What is lost or compressed when I resave a quality 12 image to quality level 8?The :geek: explanation..
JPEG compresses file size by selectively discarding data. Because it discards data, JPEG compression is referred to as lossy. A higher quality setting results in less data being discarded, but the JPEG compression method can degrade sharp detail in an image, particularly in images containing type or vector art.
Artifacts, such as wave-like patterns or blocky areas of banding, are created each time you save an image in JPEG format. These artifacts accumulate each time you resave the image to the same JPEG file; therefore, you should always save JPEG files from the original image, not from a previously saved JPEG.
HTH
JPEG compresses file size by selectively discarding data. Because it discards data, JPEG compression is referred to as lossy. A higher quality setting results in less data being discarded, but the JPEG compression method can degrade sharp detail in an image, particularly in images containing type or vector art.
Artifacts, such as wave-like patterns or blocky areas of banding, are created each time you save an image in JPEG format. These artifacts accumulate each time you resave the image to the same JPEG file; therefore, you should always save JPEG files from the original image, not from a previously saved JPEG.
HTH
There is a way of upgrading the software in my 300D so i can save RAW format but I couldn't see the point. Asked a mate - long term photographer and other 300D user - who said not to bother, just take every shot on Large Fine JPG and that should do the job.
Is this really the case?
Would it mean every shot out of the camera would need to be processed before they can be viewed on a PC?
I assume the previews on the LCD would still be produced.
This feels like a dim question so I apologise in advance if it is !
Is this really the case?
Would it mean every shot out of the camera would need to be processed before they can be viewed on a PC?
I assume the previews on the LCD would still be produced.
This feels like a dim question so I apologise in advance if it is !
I find RAW allows a bit more latency more exposure correction in situations where you don't have time to be checking and retaking shots to get the perfect exposure. Another really useful factor is being able to take one shot, process for foreground and background then merge the two and hey-presto a perfect exposure without grad filter.
Podie said:
you may as well go for the size friendly 1MB versions for web use etc.
I'd venture to suggest that's still way too big for web use. Change the image size first (eg 750px wide for posting here) then compress with JPG and you'll be amazed.
I shoot Large Fine JPG - but am careful to try to get it right in camera, so I don't have to rescue 2 stops etc
JPG is a much maligned format. True it's 'lossy', but if you can't see any difference, why struggle?
simpo two said:
I'd venture to suggest that's still way too big for web use. Change the image size first (eg 750px wide for posting here) then compress with JPG and you'll be amazed.
Yeah, fair point... not everyone has an 8meg pipe
simpo two said:
JPG is a much maligned format. True it's 'lossy', but if you can't see any difference, why struggle?
That I can't argue...
Podie said:
I'd venture to suggest that's still way too big for web use. Change the image size first (eg 750px wide for posting here) then compress with JPG and you'll be amazed.
Yeah, fair point... not everyone has an 8meg pipe
NO PUNCHLINE FROM THE NOB-GAGGER? :HEHE:
simpo two said:
JPG is a much maligned format. True it's 'lossy', but if you can't see any difference, why struggle?
That I can't argue...
No way I'd be posting 1MB images
The 1MB images are just full-res reduced quality images for my personal storage, I tend to run an action on these to make 750 pixel web friendly versions which are normally around 60kb....
The biggest problem with JPEG isn't the first time you save but as a result of the cumulative compression when you save, edit, save, edit, save again etc. You gradually get a more and more degraded image. If you know you're going to save and edit an image a few times then make sure the first save is in a lossless format such as .psd or .png
Podie said:That *used* to be true, but most decent JPEG readers now have artifact aliasing filters. These filters compensate for these effects and create an output that if saved again at the same compression level will end up with almost exactly the same file.
Artifacts, such as wave-like patterns or blocky areas of banding, are created each time you save an image in JPEG format. These artifacts accumulate each time you resave the image to the same JPEG file; therefore, you should always save JPEG files from the original image, not from a previously saved JPEG.
This has very much reduced the problem.
Alternativly you could/should move to JPEG2000 as it's wavelet compression doesn't suffer as badly in the first place from artifacts as the "DCT" compression used in the original JPEG.
You can find a paper on the "maths" behind JPEG 2000 here
www.msri.org/communications/books/Book46/files/08li.pdf
and everything else you ever wanted to know about JPEG can be found at the JPEG/JBIG website
www.jpeg.org/
Of course lots of people still use the "old" JPEG so we have a long way to go to get these better codecs in general use.
J
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