Is this sensor noise, black becomes blue/purple ??

Tinderbox (UK)

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This is an extreme version, i have high iso photo`s that the black becomes blue/purple when i increase the exposure in PS

Have a look at the photo in the link below, you can see the blue/puple in that raw without increasing the exposure at all, and the flash was not used.

Is there a way to remove this blue/purple colour so i can still increase the exposure without it showing.

http://www.filedropper.com/pb0100091

Thanks

John.
 

Amin Sabet

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I was unable to download the file, but what you describe sounds like sensor noise. There are various ways to deal with it including selectively desaturating the color in that area or changing the black point to block it out.
 

tosvus

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You should have a way in lightroom or adobe raw to increase noise reduction on color. There is also a noise reduction setting for luma, but the color is the one to use to deal with your issue.
 

Tinderbox (UK)

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I have noiseware professional plugin in PS and i have used luma and colour but it does not remove it.

John.

You should have a way in lightroom or adobe raw to increase noise reduction on color. There is also a noise reduction setting for luma, but the color is the one to use to deal with your issue.
 

kwalsh

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It's sensor noise. That's underexposed ISO6400 on the tiny little Stylus 1 sensor - so not surprising.

I can get rid of most of it in LR/ACR by moving the color NR slider up to about 50 at which point some purple remains in some shadow patches. To get rid of those dark purple areas just clip the blacks using the tone curve - drag the lower left corner to the right to push the shadows to pure black.
 

Tinderbox (UK)

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I have seen this happen with the EM5 at very high iso and it had bad horizontal banding in raw samples in a online review.

Sorry i dont have LR only PS CC

John.

It's sensor noise. That's underexposed ISO6400 on the tiny little Stylus 1 sensor - so not surprising.

I can get rid of most of it in LR/ACR by moving the color NR slider up to about 50 at which point some purple remains in some shadow patches. To get rid of those dark purple areas just clip the blacks using the tone curve - drag the lower left corner to the right to push the shadows to pure black.
 

tosvus

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When you open a Raw file in Photoshop, you should get the camera raw dialog. Underneath the histogram, there are a bunch of tabs. The third one deals with Sharpening and Noise Reduction. When you click that, in the bottom part underneath the tabs you will see Luminance (strength is the first parameter, then detail and contrast). Below that you see Color (again, strength is the first one to play with, which is just labeled Color. It will typically on my camera default to 25, you probably have to go a good bit higher, if very dark, plus small sensor camera.

Edit: Opened yours, and just some quick fiddling with those settings won't save this one. I think you would have to do some manual corrections in areas, or get a more powerful denoiser with more settings to tweak.
 

Klorenzo

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Hi.
I tried PS ARC and it does nothing to the colour noise.
Are you sure you are you need to remove chroma noise? In the sample you posted I can see none:

Subscribe to see EXIF info for this image (if available)


This is what I see as base image from the raw file (lot of chroma noise):

Subscribe to see EXIF info for this image (if available)


and this is what I got with my last attempt: fixed exposure, white balance, added fine local contrast to boost details, added a luma equalizer to polish the smaller grain. I do not why but I love to denoise images :)

Subscribe to see EXIF info for this image (if available)


Full file and darktable edit file: https://www.dropbox.com/s/tcc2ejsg8vvuud1/darktable_exported2.zip?dl=0

One hint that should be valid for any program: turn off the sharpening or rise the sharpening threshold a lot to avoid to enhance the noise too.
 

Tinderbox (UK)

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I am not bothered about the noise, it`s the blacks becoming blue/purple as i have outlined in the photo below, i have tried all the advice i have received and only reducing the exposure gets it back to black but that makes the photo too dark.

EDIT : I just had a look at the last photo you posted, how did you get the blacks to stay black when the exposure is increased?

John.

View attachment 392618
 

hazwing

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I think you are pushing the limits of what the sensor is capable of. The image is taken at high ISO and you are increasing the exposure further? I think it's not unusual to get colour shifts, in that situation.

Things you could try, but might have limited success
-reduce the black point
-in HSL - reduce the luminance of blue and purple
-brush negative exposure on the areas you want to black
-add an 'artsy filter' to purposely make everything look blue/purple/vintage :p

Or better yet, retake the photo with better lighting.
 

Tinderbox (UK)

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Some times you have to choose between a blurred image due to low shutter speed or image noise due to high iso, the image noise is easier to deal with, i dont expect to be doing this regularly.

John.
 

Klorenzo

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How much did you rise the exposure? I find out that as soon as I go over +1 EV black areas start to turn to purple. +1.3 EV is the maximum I can go with the base image.
Moving up the black point helps to contain the purple patches.

In my previous picture I rised the exposure of only +0.15 EV and then used the Tone curve to get the brightness I wanted. I can go up to +0.80 with no problems.
 

hazwing

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I think what I've done works okay with this photo, because the subject of interest does not have much blue or purple to it. My edit's have been done in lightroom because that's what I am more familiar with. I don't have photoshop, but I would assume you could do something similar.

First I pushed the exposure +1.30EV until it seemed similar to what you have posted. In lightroom there is a tab for adjusting the HSL (hue/saturation/luminance) of the various colour channels. I have reduced the luminance of blue and purple colours (in this photo -100 in these channels). This makes anything blue or purple darker. You could also reduce saturation of these colour channels as well.

I then reduce the black point slider until it seemed sorta right. I arbitarily chose -50 on this image. You tend to find as you reduce the black point, the image might darken slightly, and you might be tempted to raise EV again.

If your subject had a lot of blue or purple to it, your probably won't want to use HSL tab. Instead you could try apply negative exposure to the select regions you want to darken. As you darken these areas, the purple/blue colour shift should reduce.
 

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