Image degradation

Hi All,

One thing I learned recently was to keep away from repeated  modifications/saves to jpg files - the color transitions become very  evident, with loss of definition (pixelation) because every time it's saved it gets  compressed, and something has to go - "lossy compression". OK for a few times,  lots of saves and it starts to become evident (tried it recently). Repeatedly working on and saving an image in this format should probably be avoided. RAW or similar files is  the way to go if the camera is up to it.  Live and learn.

My cheapo Nikon Coolpix only saves in  this format (which probably means some loss from what was in the viewfinder). I've recently taken to converting the jpg files to TIFF files once  they're in the computer. Lot bigger but much more flexibility when working on them. Those with higher-end digital SLR cameras  almost certainly know about this already. Those like me who belong to the "point and shoot" brigade probably don't.

Nigel

I point and shoot Nigel, using a very old Olympus camera that still produces good pictures (IMO anyway).  My main issue with the pictures I take is that the lighting is often very poor.  Even though I have no less than 4 lamps on the subject plus the ambient lighting from other sources in the room.

Can't say I've noticed any loss of definition but maybe that's because I'm not all that aware.  I always crop and usually enhance the brightness before posting.  I still use Picasa.

John

I now do most of my work on .tif files, as you say repeated edit/save on .jpg's can be a disaster. I'll use .jpg's to post images on line or in emails, unless there's a specific reason for others to be able to download.

Here is a prime exemplar of losses due to "meddling."



I took it with my blue LED 'moonlight effect' ceiling light on.  By the time I had modified the colour, cropped it and resized it; then sharpened it, the pixellation was very noticeable.

Hi All,

Glad to see I'm not the only one who noticed this. I usually adjust sharpness, brightness, background shadow and do a bit of cropping, then save it, but I have on occasion opened and saved a jpg file quite a few times when adding text, lines or circles to highlight something. Next camera will be one that saves in RAW format (not always called this). Next best is to convert to a tif format if it needs to be worked on with photo-editing software.

I use low resolution anyway for the forum, but some of my other work requires high res images. Pity to degrade them using jpg. Quick Google search shows the issue is well known to digital photographers. I belong to the point and shoot brigade these days (ever since my local photo store closed, making buying and getting film processed a chore). I think I read somewhere that an ISO 100 resolution on 35mm film requires somewhere between 20-40 mbytes of digital imagery. I know it's a lot more complicated than that. I suspect we've become so inured to digital images we forget how good film ones were.

Nigel .

I did read somewhere to save them as PNG files and that way any cropping, etc and resaving doesn't lose sharpness, etc.

PNG files are probably a good compromise; they were supposed to replace JPEGs for Internet use but seem not to have caught on very well. They combine the qualities of both JPEG and GIF formats, but tend to be larger files than either of those.

JPEGs are highly compressed; this compression is applied each time you modify a file and save it again. If you check the before and after file sizes, you'll see what I mean.

I have had to explain to staff members where I work that when they try to send a heap of JPEGs in a zipped file, the result is often larger than the sum of the JPEGs, because of the fairly efficient compression algorithms  already applied to the JPEGs. They are trying to compress an already highly compressed file, so the overheads of keeping track of the compression means the files end up larger!

As others have said, if you can save as RAW or TIFF formats, they tend to be large but retain all of the details. Modify those, then only when you are happy with the result, save as a JPEG for online use.

Hi Jeff,

Great advice.

Nigel