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jpg and raw


10 Apr 2019 8:57AM
my grandson tells me that if i make modifications to a jpg images and save it as a separate copy there will be a reduction in image quality each time i make a copy but there is no reduction in image quality if the original image was shot in raw. What do you think

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Tianshi_angie 4 2.4k England
10 Apr 2019 9:09AM
He is right - but it isn't simple.
https://www.quora.com/Do-JPG-files-degrade-with-every-save-If-so-why

explains the process.
franken Plus
16 4.9k 4 United Kingdom
10 Apr 2019 9:44AM
If you copy a jpeg from one file to another, there's no loss of quality. If you convert a raw file to jpeg then it's at it's highest quality. (assuming it's saved at highest quality) Repeated modifications as a jpeg after that will reduce quality but should be fine for a few saves.
Tiff and psd files will not lose quality when repeatedly altered and saved.
Philh04 Plus
13 2.0k United Kingdom
10 Apr 2019 9:45AM
In simple terms any jpg file whether created from a raw file or not will degrade after multiple edits and saves, because information is thrown away each time, however this will be lessened if you create a copy of the file and edit that and save it as a separate file. It doesn't make any difference if the original was shot in raw (a raw file will never be altered and will maintain its quality, but a raster file produced from it will degrade after multiple edits and saves).

So editing pixels = destructive
editing raw data = nondestructive.


Quote:Tiff and psd files will not lose quality when repeatedly altered and saved.

Actually they do but to a much lesser extent....
thewilliam2 2 1.1k
10 Apr 2019 10:08AM
I was taught never to work on the original but always a copy.

Our workflow has always been to shoot RAW and make 16 bit TIFFs. Working with 16 bit was essential in the days of white backgrounds because it avoided the tide-marks that the larger steps of 8 bit, and JPEG images are 8 bit, often caused.

If the worst came to the worst, the original RAW (or indeed JPEG) was there for another attempt but we'd have lost all the post-production work.

If we intend to do significant work in post, why use JPEG at all in these days of cheap storage, unless it's a final conversion to send to the printer?

Sports and events photographers generally shoot JPEG because it probably won't be manipulated on site and it can get to the picture editor's desk or printer more quickly.
Dave_Canon 12 1.5k United Kingdom
10 Apr 2019 12:32PM
The Raw file is non-destructive as are any TIFF or PSD files you produce from them. There is no problem editing a Raw file because the editing changes are recorded separately and the Raw data remains intact. When you render a Raw file (e.g. export to PS as say 16 bit TIFF) then a new file is produced and the Raw file remains intact. The Raw editing is stored as instructions in the catalogue for LR and often in a separate sidecar file. So there is no problem editing the original Raw file.

It is easier enough to demonstrate the destructive effects of saving re-editing and saving again a JPEG file. The damage is most easily seen in an image with details and lines. A good workflow would be to do as much editing as feasible using the Raw editor (e.g. LR) then complete editing as a 16bit TIFF or PSD file (e.g. PS). You may have to reduce to 8 bits if not using PS. I retain my final edited files in TIFF or PSD form and use these for printing or to produce JPEG files for projecting or web as required. I do not store the JPEG files permanently but do store the final edited TIFF files (and, of course the Raw files).

Dave
Philh04 Plus
13 2.0k United Kingdom
10 Apr 2019 1:00PM

Quote:The Raw file is non-destructive as are any TIFF or PSD files you produce from them.

Correct that any editing to a Raw file is non-destructive, but TIFF and PSD editing is destructive, you can use layers etc for a non-destructive workflow but the minute you export or flatten for export the edits will be applied which will be destructive.
Dave_Canon 12 1.5k United Kingdom
10 Apr 2019 2:40PM
I used the term "destructive" simply because it was used earlier in the thread. Strictly, TIFF and PSD are lossless formats. The topic was raised about the difference between lossless formats and lossy JPEG. The destruction that you refer to is self inflicted whereas JPEG deterioration is an unwanted side effect. A Raw file can also be destroyed by deleting it.

Dave
Tianshi_angie 4 2.4k England
10 Apr 2019 2:57PM
But a Tiff can be much larger than the original Raw file. I have just checked this - a specific Raw file is 23.59Mb the processed Tiff of that file (Layers merged) is 47.33Mb. I believe that is because the processing I have done has added information to the file in addition to Copyright etc.
Philh04 Plus
13 2.0k United Kingdom
10 Apr 2019 2:57PM

Quote:I used the term "destructive" simply because it was used earlier in the thread. Strictly, TIFF and PSD are lossless formats. The topic was raised about the difference between lossless formats and lossy JPEG. The destruction that you refer to is self inflicted whereas JPEG deterioration is an unwanted side effect. A Raw file can also be destroyed by deleting it.

Dave


Wasn't disagreeing, it was just that someone inexperienced reading that part of your reply might wrongly assume that TIFF and PSD editing was non-destructive which of course it isn't and as you say 'self inflicted' (I actually like that term)

Best wishes
Philh04 Plus
13 2.0k United Kingdom
10 Apr 2019 3:04PM

Quote:But a Tiff can be much larger than the original Raw file. I have just checked this - a specific Raw file is 23.59Mb the processed Tiff of that file (Layers merged) is 47.33Mb. I believe that is because the processing I have done has added information to the file in addition to Copyright etc.

A raw file is just that, raw data from the sensor, when that data is translated to a TIFF file three channels are created (RGB), therefore the TIFF file will be on average three times the size of a raw file.
Tianshi_angie 4 2.4k England
10 Apr 2019 3:22PM
Thanks Phil - makes it clearer.

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