# Question about JPG...



## Dori1960 (May 19, 2011)

Maybe someone here can educate me about saving in .jpg and loss of info, compression. I have asked in other forums but still haven't found my teacher. I know when I save, info is lost and the file becomes smaller, quality poorer. Why? 
Why is .jpg the most often used format if it degrades an image?
Probably more questions to follow.

Thanks, Dori


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## zuluclayman (Dec 16, 2005)

jpg is a lossy compression method - each time you save an image you lose a bit more data - so if you were to import a jpg image from your camera unless you have your camera set to save only in RAW format your camera will have already used some compression algorithm on the data picked up by your camera's sensor. You can set what amount of compression your camera uses in this first step.
When you open it in your image editor (Photoshop et al) and do some post-processing then save it again you will lose some more data - again in Photoshop you can decide how much compression is used (the sliding scale from 0-12)
If you do this a number of times you will gradually begin to notice the compression artefacts appear - colours along edges become wrong, sometimes where there may have been a gradual colour tone change it jumps more severely & eventually some pixellation will occur.
Why is jpg the most common picture file format? because it can deliver a reasonable quality image for a reasonable size file. When it was developed storage on computers was much much smaller than today and sending large files by email etc was much slower so file sizes had to be kept to the minimum they could with the best image quality being kept as well - jpg did that.
These days it has become the image file format of choice for those and commercial reasons - most software & hardware (cross platform compatability is another factor here) is enabled to deal with jpgs similarly to how VHS became the commercial standard even though beta was a better quality.
With the advent of DSLR cameras and their increasing sensor (and storage) capabilities the RAW format is used more and more often by serious photographers - RAW format captures and saves the image with all the data the sensor picks up intact - it is the eqivalent of unprocessed but exposed film - all the data is there, what you do with it after that is up to you :grin:

hope this helps and isn't too confusing :grin:


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## WereBo (Apr 5, 2008)

If storage space on your PC isn't a problem, folks whos camera doesn't save as .RAW can save your work-images in .BMP (bitmap) or .TIFF (can't remember what) format - Although they're usually huge files, they save every detail intact. Just save a copy as .jpg (with as little compression as is feasible to file-size) after everything's ready for publishing on the the interweb :wink:


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## zuluclayman (Dec 16, 2005)

TIFF is the next best to RAW - most cameras have an option to save images as TIFF - as WereBo says: large file size but data mostly intact


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## Dori1960 (May 19, 2011)

Thanks so much!! I finally 'get' it!


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