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I have a RAW photo in aperture that has quite a lot of noise. When I export the photo to JPEG (and TIFF/PSD, 16 bit) I get a strange square grid like pattern on the photo.

Here is an example of the issue. On the left is the RAW, and on the right is an exported TIFF image.

Is there any reason for this and what can I do to resolve it so there is no grid like pattern?

Example of issue

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1 Answer 1

up vote 2 down vote accepted

The basic problem appears to be that the photo, at least the top part where the two shelves are, is grossly underexposed. That means the signal to noise ratio is already quite low.

Look closely at the left picture and you will see some of the grid pattern evident. This is probably some repetitive noise in your sensor. Normally you wouldn't see it, but the actual image information is so small relative to the noise floor that the noise appears visibly in the picture.

The reason you see it more in the right picture is because someone attempted to brighten the picture a little or otherwise get more detail in the dark areas when there was little to be had. This amplified the grid noise to make it more apparent, but it was there all along.

The solution is to use proper exposure. There is basically nothing you can do to recover from low signal to noise ratio unless you are willing to give up spacial resolution. Put another way, the information to make a good picture simply isn't present in the original.

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Thanks for the explanation. I wondered why the grid pattern was more prominent in the TIFF when this was just an export of the RAW you see here on the left? No alterations have been made to it. I just wanted an export that looked like the RAW! –  Oliver Joseph Ash Jan 2 '13 at 14:08
    
@Oliver: But alterations have been made. Look closely at some of the nearly but not totally dark areas in the right picture and see that they are darker in the left. There is clearly some gain in the dark areas from the left picture to the right picture. –  Olin Lathrop Jan 2 '13 at 14:50
    
Alterations have been made to the RAW, yes, but those are seen on the screenshot I posted. I agree that it looks as if the exported image has been altered as well, but it is just an export with no alterations. Unless Aperture is making any alterations… –  Oliver Joseph Ash Jan 2 '13 at 14:51
    
@Oliver: Just look at the two pictures. Clearly there are differences. Exactly where in the software they come from is irrelevant to the discussion here. –  Olin Lathrop Jan 2 '13 at 15:27
    
All I wanted to know is how I could get an export that looked like the original… –  Oliver Joseph Ash Jan 2 '13 at 15:28

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