Whats with the purple thatch type noise im getting ?

gus · January 15, 2006

I shot maybe 20 shots & most have this to diff degrees. This is one of the worst shots.

Didnt expect much as it is a very hot, humid night but this is not normal.

Date Taken:2006-01-15 20:42:40Date Modified:2006-01-16 05:30:29Make:CanonModel: Canon EOS 20D Size: 5120x3413 Bytes: 2342540 Aperture: f/5.6 ISO: 100 Focal Length: 400mm Exposure Time: 0.0015s (1/640)Flash:Flash did not fire, compulsory flash modeExposure Program:Shutter priorityExposure Bias:0

DavidTO · January 15, 2006

That's noise from PS trying to make a decent exposure out of something it sees as being underexposed. You shot RAW? PS automatically makes its best guess about settings. It pushed it so much you got noise.

wxwax · January 15, 2006

Yikes. That looks like the kind of noise I'd expect with a super long exposure. I'm curious to hear what others think.

gus · January 15, 2006

DavidTO wrote:

That's noise from PS trying to make a decent exposure out of something it sees as being underexposed. You shot RAW? PS automatically makes its best guess about settings. It pushed it so much you got noise.

er...dave...the exif says 20D & 400mm lens

DavidTO · January 15, 2006

Humungus wrote:

er...dave...the exif says 20D & 400mm lens

Yeah, so?

PS will set the exposure, shadows, highlights, etc based on its best guess. It pushed your image too far, and you got a ton of noise. You need to back off on the exposure settings in RAW, if you did shoot RAW...

gus · January 15, 2006

DavidTO wrote:

Yeah, so?

PS will set the exposure, shadows, highlights, etc based on its best guess. It pushed your image too far, and you got a ton of noise. You need to back off on the exposure settings in RAW, if you did shoot RAW...

No PS what-so-ever ...nil...none...zip.

Straight from the camera.

Yep raw.

DavidTO · January 15, 2006

Humungus wrote:

No PS what-so-ever ...nil...none...zip.

Straight from the camera.

Yep raw.

Well, if you shot RAW, then PS got its grubby little hands on it and tried to make a decent exposure out of it. It's a feature that's on by default. Guaranteed that's not "as shot" as far as exposure, highlights, shadows, etc. goes. I've seen this too many times....it's boosting the exposure too much and you're getting noise.

Go back to ACR and lower the exposure. See what happens.

gus · January 15, 2006

ok...but only once you tell me what arc is.

gus · January 15, 2006

Of all the shots i took...it only seems apparent on the ones that had cloud over the moon...the ones with a full strong moon are ok. These were all only seconds apart as the cloud was moving fast.

DavidTO · January 15, 2006

Humungus wrote:

ok...but only once you tell me what arc is.

don't know what arc is

but ACR is Adobe Camera Raw. It's what converts your RAW to JPEG or TIFF, and it's trying to do something similar to your camera meter. It's trying to normalize the image, but this image isn't "normal" it's a whole lotta black with light gray in the middle. ACR muddles it up, and you have to fix it.

gus · January 15, 2006

Mate if i tried to understand half the terms you blokes use in here i would never get any photography done. I just pick the odd one up as i go.

So when i open the shot in CS2...i look where ?

DavidTO · January 15, 2006

Humungus wrote:

Mate if i tried to understand half the terms you blokes use in here i would never get any photography done. I just pick the odd one up as i go.

So when i open the shot in CS2...i look where ?

Adjust exposure down, maybe shadows up, brightness down...some combo of those. You need to darken the image.

DavidTO · January 15, 2006

And Gus, seriously:

How on earth do you end up with such great images when you don't even know what I'm talking about in setting your exposure in RAW? Amazing. Beautiful galleries, you've got, and a great eye to go with it. You're just damn lucky, I guess...

gus · January 15, 2006

ok...thats just basic RAW stuff, i thought it was something new.

I have already done all this over & over.

I just have not seen this come from the camera before & ive done a lot of moon shots. Maybe i have changed the settings of a type of default.

Tks mate, will give it another go.

gus · January 15, 2006

DavidTO wrote:

And Gus, seriously:

How on earth do you end up with such great images when you don't even know what I'm talking about in setting your exposure in RAW? Amazing. Beautiful galleries, you've got, and a great eye to go with it. You're just damn lucky, I guess...

Tks mate but i wish i did read more so i could use CS2 better which is why i like kelbys book so much. I just follow the bouncing ball.

Steve Cavigliano · January 15, 2006

Humungus wrote:

Mate if i tried to understand half the terms you blokes use in here i would never get any photography done. I just pick the odd one up as i go.
quote]

:giggle :lol

Now you know how we feel when we read your posts Gus...lol

OK, on topic, did you get a jpg along with your RAW? Or do you only shoot RAW? I ask because I see lots of things in my RAW images that are corrected (by in-cam processing) in the associated jpgs. For instance, because I shoot lots of birds against bright skies, I get major cyan fringing around talons and wingtips when I use my Bigma or the 400mm F5.6L. I have to correct it after conversion if processing a RAW file. But when I open it's associated jpg, the fringing isn't there. If you have jpgs to compare with, I'd be interested to know whether you notice the same phenomenon viewing them.

I have seen this "screendoor" pattern before on some of my Sony IR images. I don't know what caused it though I couldn't salvage the pics either

Steve

wxwax · January 15, 2006

What would be cool would be to see your histogram for this shot. Let's see where the light bulge is.

If it's too far to the center or the left (and it sounds like it is, based on your comments about the cloudy shots have noise and the uncloudy shots being clean) then that will support what David says - Photoshop is trying to give you a decent exposure for what is actually an under-exposed shot.

Sam · January 15, 2006

Gus,

To me (like others) it just looks like it's been underexposed, and when the exposure is boosted in the RAW conversion, it will create noise.

Can you send / post the original RAW file?

I tried the other night to get a shot of the full moon and screwed up.

Had the ISO set on 800. Had to put in -2.35 negitive exposure. Not good but better than 2.35 positive exposure compensation.

Some one here told me to shoot the full moon like daylight. I use manual setting of f11, and 1/100 to 1/125, and check the hystogram.

Not what I wanted but as you can see the sky is noise free. Taken with 70-200 f2.8

Sam

dallas · January 15, 2006

I just read a long technical review by Born, about the D200 on Dpreview, in which he describes "striping", and this looks like what he was talking about. I'm not an expert, or pretend to undrerstanding this problem, but do some research and you may find the answer.

Shay Stephens · January 16, 2006

I face this type of problem all the time. What you are seeing is a two fold problem.

1) Canon cameras have those stripes in the image. It was worse with the 10D and got better by a little with the 20D, but not enough to go away. It shows up when the image is brightened beyond maybe 1.6 stops. You can help downplay the effect by doing some chromas noise reduction.

2) Adobe Camera RAW (ACR) is responsible for making a RAW file usable in Photoshop. Whether you mess with the settings or not, by default, ACR will apply auto settings for exposure, black point, contrast and something else that escapes me right now. In this instance, it cranked the exposure too far and the stripe artifacts are visible.

Remedy, just reopen the RAW file and take the exposure slider down, make the black point higher, and it should look better. If not, then the photo is just too underexposed to be usable, toss it.

DoctorIt · January 16, 2006

If you didn't use the new fangled CS2, you wouldn't have this problem. CS actually assumed you had half a brain, and the ACR there started everything off as "0".

If thats not it, take a jpg and see if you get the same problem (I doubt it).

gus · January 16, 2006

DavidTO wrote:

That's noise from PS trying to make a decent exposure out of something it sees as being underexposed. You shot RAW? PS automatically makes its best guess about settings. It pushed it so much you got noise.

You see mate....i thought you ment a 'point & shoot'

pathfinder · January 16, 2006

Like Shay and David said, the purple striping is from the ACR trying to get some detail in the area of the sky that is not there - the sky around the moon is deep black if you expose correctly for the face of the moon which is sunlit, but space is deeep deeep black -

So just adjust the black point slider to make the area far from the moon totally black 0,0,0 - of use the black point eyedropper to do the same thing and then the purple hatching will be replaced by deep black.

gus · January 16, 2006

Ok...thanks everyone for your efforts here. I was worried i may have experienced a 'cook off' on my sensor when i did that one hour astro shot last month.

I can stop that ugly stuff when i reduce the settings in raw but it just hasnt done it before. At the end of the day it is just too humid here (often sits around 90%) to get a good shot at the moment. The only good one i got was in winter.

pathfinder · January 16, 2006

Don't feel too bad 'gus - Humid air is just blurry to shoot through. My better lunar shots were all in winter or very early spring here in the Northern Hemisphere - February or March. That is not the cause of the cross hatching tho.

I was talking at lunch with mereimage about the light in the Antarctic - and the fact that the air is so clear and pristine due to the absence of moisture ane dust - probably similar effects were present in New Mexico when Georgia O'Keefe settled there for the light as well. G'dya to ya!

gus · January 16, 2006

yep..we have soupy air in summer thats for sure mate. I will wait for winter as the air gets a good deal dryer.

DavidTO · January 16, 2006

Shay Stephens wrote:

Canon cameras have those stripes in the image.

Are you saying Nikon doesn't? Curious...

Shay Stephens · January 16, 2006

I can't say definitively, but this particular thing is Canon related. I never had it with Sony. But the Sony was CCD and Canon is CMOS. So it could be a CMOS thing

DavidTO wrote:

Are you saying Nikon doesn't? Curious...

DoctorIt · January 16, 2006

Humungus wrote:

yep..we have soupy air in summer thats for sure mate. I will wait for winter as the air gets a good deal dryer.

winter... you mean when you have to wear a long sleeve shirt in the morning?

gus · January 17, 2006

DoctorIt wrote:

winter... you mean when you have to wear a long sleeve shirt in the morning?

If im doing 4am starts i will... but i do often have to shut the balcony door at night.

Whats with the purple thatch type noise im getting ?

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