Photo losing quality


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Apr 12, 2008
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#1
Hi i wanna know if it's true that a photo will lose quality each time the photo is copied or modified. thanks...:)
 

spidey89

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#2
from what i know,that occurs with jpeg,not sure about other formats,I don't think RAW is affected though
 

photobum

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Hi i wanna know if it's true that a photo will lose quality each time the photo is copied or modified. thanks...:)
Copied to where? Modified through what means? Photo in hard copy or soft copy? Please clarify so that we can help you better.
 

#4
Hi i wanna know if it's true that a photo will lose quality each time the photo is copied or modified. thanks...:)
Usually that is only true if you are talking about compression formats like JPG or JPEG ( same thing...difference way of writing it) Anyway... it is true that each time you open it and then resave it, it WILL lose quality. Quality is subjective but what I think it should be is you look picture data or details.

Here is what happens when you save a photo to Jpeg. Now depending on how much compression you choose to specify as part of the condition to save the photo to jpg. It will the first time you save it contribute to some lost in details/data. Initially you might not notice it but as you start to zoom in closer to lines and contrasting portions, you will start to see some artifacts. What those artifact are can be seen already in the most extreme case. Take a photo you have that is say 600 x 800. Now you save that photo as a jpg and select 90% which is the minimum of compression in some s/w or it could be stated as "low, medium, high".eg.. In any case, selecting that you want the less amount of compress will result in a space saving size that is like maybe half od what your original photo would be.

Now save another time under a difference name but this time select the maximum compress to make the file size as small as possible. This time the compression will product a micro small file size of your photo. Now you open both this jpg photos up and place them side by side, you will see that the one with the most compression( and smaller file size) will look really bad, lots of out of place pixel/colour hues..etc.

If you did not know by now, jpg compression is like mp3. To make a photo or music file size smaller while it still keep it's actual pixel size ( as in this example I mentioned 600 x 800) well the algorithm written to do the compression in the photo or music will start to take away unneeded colour and pixels. Anything that is very similar and hard to see by your eyes, the program will take it away. Same with music. all the high or low that human ears can not pickup will be the first to go.

Problem is as you increase the compression rate, they start to compromise things by taking away more and more stuff...now it might include stuff you really want still in the photo or music. So the more you compress the more data/details you loose.

NOW...coming back to your question. Each time you open a jpeg, the jpeg algorithm will work it's magic on that photo. It will take whatever details is left of that photo and try to assemble it all back again. What that means is...everytime you open that same jpg photo, it might look a bit difference as the assembling does not follow a given path. But so long as you don't re save it...the quality stays the same.

Now imagine you open the file and resave it and the open again and resave it....tens of times. Each time you do this, that photo will start to 'evolve' (as the algorithm will each time see what is there and then when you resave it, it will re-run compress algorithm again treating what it see as a new image.) and in this case it start to look worst over time as more data is lost and re jumbling just makes a messy shot...more messy as you keep re compressing it time and time again. heh

The only way you can limit that is the jpeg file you have taken from the camera, keep a copy of it. Only open it one time and use that open copy as your working copy and save it under a new name. Store away the original jpg that came out of your camera. A few times open an dsave will not matter too much lah BUT!!!....when you do save it, use "save as" as like in Photoshop for example, when you just clip "save", it will just save without further prompting you. Problem is what compression will photoshop take? What if it was maximum compression? So use "save as" sa this will open a window setting box that let you select compression rate fot that photo. Always select 10 or 11 for the less amount of compression. 12 is really overkill. This is mainly for those shooting in jpg.

IN RAW, TIFF..etc this are non-compress photo file format. Really what you see is what you get each and everytime you open and save to it.

Hope that help....though it sound abit complicated the way I try to explain it heheh..
 

Rashkae

Senior Member
Nov 28, 2005
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#5
Usually that is only true if you are talking about compression formats like JPG or JPEG ( same thing...difference way of writing it) Anyway... it is true that each time you open it and then resave it, it WILL lose quality. Quality is subjective but what I think it should be is you look picture data or details.
Please note... sammy888 is referring to OPENING and RE-SAVING a jpeg.

if all you are doing is copying, of course it WILL NOT lose quality. It's a digital file.

The myth about losing quality came from the old magnetic audio tape days...
 

Apr 12, 2008
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#6
Thanks sammy888 for explaining in detail. I really appreciate it. I'll follow your advice.
 

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