Blue halo - what is causing it?

[hillwalkinggirl]

I've noticed on some of my photos a blue halo surrounding dark objects which are against light. This is noticeable when viewing a 12m pixel image at 100%.
I have cropped this photo so that I can show a small area at high resolution. The exif data is left in and can be read in a viewer.

Any ideas would be appreciated please.

 

[magicaxeman]

That's CA or otherwise known as chromatic aberration.

It's caused by the lens not focusing all the different wavelengths of light to the same point often the fringing is blue but it can be yellowish as well.

Basically cheaper lenses will usually be the culprits displaying this tendency, more expensive lenses tend to use 1 or more elements made of SD glass, this helps to combat it, lenses marked APO, which have a true triplet objective or several elements made of SD glass are usually pretty much CA free.

It can be removed to a degree in software, there are several actions for photoshop around that will help to deal with CA/blue fringing.

 

[hillwalkinggirl]

That's CA or otherwise known as chromatic aberration.

It's caused by the lens not focusing all the different wavelengths of light to the same point often the fringing is blue but it can be yellowish as well.

Basically cheaper lenses will usually be the culprits displaying this tendency, more expensive lenses tend to use 1 or more elements made of SD glass, this helps to combat it, lenses marked APO, which have a true triplet objective or several elements made of SD glass are usually pretty much CA free.

It can be removed to a degree in software, there are several actions for photoshop around that will help to deal with CA/blue fringing.

Thanks Ian. I thought that it might be CA/blue fringing but I have tried to improve it in Photoshop but it wont remove it. I know I'm only using a compact and not my DSLR but it is a reasonably expensive one - The new TZ10, and I am wondering if there are any adjustments in camera that would help solve the problem.

 

[simonbell19]

Its all about the quality of the glass, bad glass lots of CA, good glass less CA

 

[ki_user]

Thanks Ian. I thought that it might be CA/blue fringing but I have tried to improve it in Photoshop but it wont remove it. I know I'm only using a compact and not my DSLR but it is a reasonably expensive one - The new TZ10, and I am wondering if there are any adjustments in camera that would help solve the problem.

How have you tried to get rid of it in PS, was it in the lens correction?

 

[hillwalkinggirl]

How have you tried to get rid of it in PS, was it in the lens correction?

Yes that's what I tried but it didn't help at all. I also have a Panasonic FX500 and I am not getting the problem with that. It's not really cheap glass as they both have a Leica lens.

 

[Pete Bird]

If you want to have this as a keeper then there are several ways you can do it without too much bother.
I dont think it is just a CA as you have a Blue CA inside the cows black part of its back.
I think it is the camera and the angle it was taken, just an unfortunate trick of the light.

 

[hillwalkinggirl]

If you want to have this as a keeper then there are several ways you can do it without too much bother.
I dont think it is just a CA as you have a Blue CA inside the cows black part of its back.
I think it is the camera and the angle it was taken, just an unfortunate trick of the light.

Thanks Pete. I don't want to have this as a keeper as it was a pretty rubbish photo anyway. I think you could be right as I have just looked through all the photos I have taken with this camera and I notice all the photos that I took in landscape mode on the same day, had the same problem, but the photos I took in aperture mode were OK.

 

[Cyb]

I would tell you that it is not lens chromatic aberration but caused by the cameras sensor/photosites not being able to judge the difference between a strong dark / light area thus leaving a ridge between the two areas – but hey what do I know.:shrug:

 

[loplyg]

You know, this may also be caused by you just getting too few pixels on the details.

On the near cow, it may also be a strange effect as it's a hairy animal. Sometimes you get a layer of hair which is kind of tangential to the bit of the cow that's on-axis with your photo, if you see what I mean, and it can make a kind of glowing effect like that.

Or it could just be CA

 

[trencheel303]

For a compact that's actually pretty good, considering this is only a crop of an image.

 

[Splog]

Hi Barbara

I'm not sure that's CA either Look at the two cows in the background they have a very distinct white border around them! Is this a raw file or have you used some style or processing setting in camera?

Edit: Forgot to ask: Were you using any zoom on the shot?

(sorry, but I can't get the exif data from the shot)

 

[hillwalkinggirl]

For a compact that's actually pretty good, considering this is only a crop of an image.

I must admit I'm very pleased with the camera overall. Reviews of the camera state that the intelligent mode has problems, so I didn't use this. I've never really been a fan of auto modes, so I think a little tinkering with manual and spot metering will probably resolve this. At least the compacts always with me whereas my DSLR is usually in the house.

 

[CT]

It actually doesn't look a bit like CA. What I suspect it is, is that in viewing the image at full size, you're seeing the limits of the resolving power of that tiny sensor on your compact camera which is producing this fringing on this high contrast subject.

Viewing images at 1:1 is a challenge even for a DSLR with it's much larger sensor. If you only see the fringing at large image sizes, you're probably worrying unduly, I suspect the fringing would be invisible at any size you're likely to print at?

 

[diggerz]

Stop taking pictures of cows?

 

[hillwalkinggirl]

Hi Barbara

I'm not sure that's CA either Look at the two cows in the background they have a very distinct white border around them! Is this a raw file or have you used some style or processing setting in camera?

Edit: Forgot to ask: Were you using any zoom on the shot?

(sorry, but I can't get the exif data from the shot)

No it's not a RAW file, this camera doesn't have it, and yes I was using some zoom. The camera is wide angle 25mm (35mm equiv) with 12x zoom. I think I spot a clue in the exif data, contrast is +21. This was set automatically in Landscape mode. In aperture priority contrast is not adjusted. This seems like a good reason not to use auto modes.

Standard Information
Make: Panasonic
Model: DMC-TZ10
Software: Adobe Photoshop CS3 Windows
ImageSize: 3320x2496
CreateDate: 2010:07:11 21:41:52+01:00
ModifyDate: 2010:07:11 21:41:52+01:00
DateTimeOriginal: 2010:07:11 12:14:39+01:00
ExposureTime: 1/400"
Aperture: F5.0
MaxAperture: F3.3
CircleOfConfusion: 0.005 mm
HyperfocalDistance: 2.52 m
ExposureProgram: Landscape
ExposureBiasValue: 0
MeteringMode: Multi-segment
Flash: Off
ISO: 125
WhiteBalance: As Shot
FocalLength: 7.9 mm
FocalLength35efl: 7.9 mm (35 mm equivalent: 48.0 mm)
SensingMethod: One-chip color area
SceneType: Directly photographed
ColorSpace: Unknown (-1)
Contrast: +21
Saturation: 0
Sharpness: 0

 

[hillwalkinggirl]

It actually doesn't look a bit like CA. What I suspect it is, is that in viewing the image at full size, you're seeing the limits of the resolving power of that tiny sensor on your compact camera which is producing this fringing on this high contrast subject.

Viewing images at 1:1 is a challenge even for a DSLR with it's much larger sensor. If you only see the fringing at large image sizes, you're probably worrying unduly, I suspect the fringing would be invisible at any size you're likely to print at?

I agree it's not really a problem, but I was always one of those children who always asked "why"

Stop taking pictures of cows?

The big black bum was the biggest bull you've ever seen. I'm glad I had a fence between me and him.

 

[CT]

I see looking at that exif data Barabara that contrast is set at +21. I don't know how that equates to the default settings, but increased contrast might cause this fringing.

It can also be induced in processing by over-sharpening and the use of feathered masks can often leave this type of halo

 

[Splog]

I see looking at that exif data Barabara that contrast is set at +21. I don't know how that equates to the default settings, but increased contrast might cause this fringing.

It can also be induced in processing by over-sharpening and the use of feathered masks can often leave this type of halo

I was just about to say something very similar Except for the feathered masks bit ..... as I'm not sure what that is

 

[CT]

I was just about to say something very similar Except for the feathered masks bit ..... as I'm not sure what that is

LOL. A feathered mask is mask which you apply around a subject to darken it's surroundings (for example). It's usual to feather the mask by a few pixels to give a gradual fading effect so there isn't a hard line visible where you've increased the contrast. The problem is the feathering starts from where your original mask is, and if you don't have a snug enough fit around your main subject you can get this sort of fringing as it leaves a lighter area when you darken the surroundings.

Does that make any sense at all?

 

[CT]

Barbara, it's quite usual for Landscape settings to increase colour saturation and contrast, so I would guess you may have sussed the problem yourself if you're not getting the halos in AV Mode.

 

[Splog]

LOL. A feathered mask is mask which you apply around a subject to darken it's surroundings (for example). It's usual to feather the mask by a few pixels to give a gradual fading effect so there isn't a hard line visible where you've increased the contrast. The problem is the featheting starts from where your original mask is, and if you don't have a snug enough fit around your main subject you can get this sort of fringing as it leaves a lighter area when you darken the surroundings.

Does that make any sense at all?

Yes it does. It makes perfect sense Sorry, I was having a completely dumb (or should that read beer) moment Just never thought of feathering as a mask, but you're spot on it is a mask, I usually just see it as a tool property! ....

 

[HoppyUK]

That's not CA and doesn't look anything like CA.

It's a JPEG processing artifact.

Edit: not sure you can do much about it. Compact JPEGs are usually massively over processed to try and get something decent out of their tiny sensors. The actual sensor area you're viewing there is about the size of a pin head. It doesn't do to look too closely at files from compacts, they can't stand much scrutiny at 100%, which is fair enough really. There's all sorts of weird stuff going on and the lens is almost nothing more than a starting point

 

[hillwalkinggirl]

I see looking at that exif data Barabara that contrast is set at +21. I don't know how that equates to the default settings, but increased contrast might cause this fringing.

It can also be induced in processing by over-sharpening and the use of feathered masks can often leave this type of halo

I was just about to say something very similar Except for the feathered masks bit ..... as I'm not sure what that is

Barbara, it's quite usual for Landscape settings to increase colour saturation and contrast, so I would guess you may have sussed the problem yourself if you're not getting the halos in AV Mode.

Thanks everyone, I'm going to do a test if the rain holds off, trying different settings and then checking the exif. I'm curious to know what default settings the camera uses for these auto modes. Then I think I'll forget the auto modes as I don't like my camera being a control freak.:nono:

That's not CA and doesn't look anything like CA.

It's a JPEG processing artifact.

Edit: not sure you can do much about it. Compact JPEGs are usually massively over processed to try and get something decent out of their tiny sensors. The actual sensor area you're viewing there is about the size of a pin head. It doesn't do to look too closely at files from compacts, they can't stand much scrutiny at 100%, which is fair enough really. There's all sorts of weird stuff going on and the lens is almost nothing more than a starting point

I take your point, but I know that the standard wont be anything comparable to my D80 but it should be better than my other compacts as it's a Leica ASPH lens with an 11mm CCD. I'm not too sure how they work out sensor sizes but I imagined that the 11mm would represent the actual area of the sensor so at a rough guess I imaged it would be 3.3mm x 3.3mm which would be a lot bigger than a pin head. Can anyone clarify this for me please.

This is the spec of my camera:
Panasonic Lumix DMC-ZS7/TZ10 Spcecifications

Image Sensor: 12.1 million effective pixels.
Metering: Multiple zone, centre-weighted and spot.
Sensor Size: 11mm CCD.
Lens: Leica DC Vario-Elmar f3.3-4.9/4.1-49.2mm (25-300mm as 35 SLR equivalent).
Shutter Speed: 60 to 1/2000 second.
Continuous Shooting: 2.3 fps.
Memory: SD, SDHC, SDXC cards plus 15MB internal memory.
Image Sizes (pixels): 4000×3000, 3264×2448, 2560×1920, 2048×1536, 640×480.
Movies: 1280×720, 848×480, 640×480, 320×240 at 30 fps.
LCD Screen: 7.6cm LCD (460,800 pixels).
File Formats: JPEG, Motion JPEG, AVCHD Lite.
ISO Sensitivity: Auto, 80 to 6400.
Interface: USB 2.0, HDMI, AV.
Power: Rechargeable lithium ion battery, DC input.
Dimensions: 103.3×59.6×32.6 WHDmm.
Weight: 218 g (inc battery and card).

 

[HoppyUK]

Barbara, the way compact sensors are described is weird and dates back to some old TV tube standards that take a bit of getting your head around. Here's an explanation from DPReview http://www.dpreview.com/learn/?/Glossary/Camera_System/sensor_sizes_01.htm

The diagonal of your "2.33in" sensor is 11mm, 8.8 x 6.6mm. So the area we're looking at in your OP enlargement is about the size of a pin head!

What I'm saying about the post processing bit is with the frankly miniscule amount of image data the camera has to work with (forget 12m pixels or whatever, that's just marketing) the JPEG engine gives the image a serious makeover to try and make it look half decent - basically a digital airbrushing. Among the many things it does is try to create artificial lines between areas of light/dark tone to enhance the impression of sharpness and that's what you're seeing.

To be fair, that's the basis of most sharpening procedures and all digital images need at least some of that, but compacts just need a lot more of it. What they do to noise is even worse, smearing away a lot of detail to conceal the noise, then trying to pull back the lost sharpness with more of these edge enhancement procedures.

And with respect to your Leica lens, which I strongly suspect has got nothing more to do with Leica than the name, will also be benefiting from distortion control in the JPEG engine, vignetting reduction, and the digital reduction of CA. Frankly it's not possible to produce lenses with the range of your 25-300mm equivalent zoom without a great deal of digital processing help going on behind the scenes. Manufacturers don't like to talk about this much and prefer to pretend that it's all down to their wonderful lenses, but if you could get a naked Raw file out of your camera you would see the reality of what's actually recorded by the sensor as original data, and it wouldn't be pretty.

Not dissing your camera or even compacts in general, but they have their limitations and looking at 100% images is going to reveal them. Pixel peeping is bad for your health

 

[Donki]

say is the incamera PP that goes on inside compacts, most of the time there is alot to make their pictures look all vibrant and sparkley like .

 

[tdodd]

The problem looks to me like a case of the most unsympathetic sharpening I think I've ever seen. When you (or the camera) applies sharpening to an image it identifies boundaries (i.e. edges) between contrasting pixels and makes the dark pixels at the edge a little darker and the light pixels at the edge a little lighter. This creates the impression of a better defined edge, rather than one which might be a little fuzzy/soft.

If the effect here was simply one of excessive contrast then you would get very deep blacks and a pale sky, but not this odd halo at the boundary, unless as Hoppy says this is a JPEG artefact. The impression I get is not that this is a JPEG compressoion problem but sharpening gone absolutely nuts. You can't really see the blacks getting any blacker, because they are already so dark, but the halo in the sky is a huge clue (IMHO) that sharpening has gone way OTT in "enhancing", if I dare call it that, the contrast in the paler tone at the edge. Has this image been double sharpened or is that really what the camera is spewing out? To determine if it is a sharpening problem simply reduce sharpening as much as possible in the camera and then see how things look.

Just my two cents.

EDIT : p.s. here's a 100% crop from one of my images, which was absolutely fine until I added maximum sharpening in Lightroom, and now looks equally sh!tty. OK, my ham fisted effort is perhaps even worse, but you get the idea - this is a sharpening halo, not a JPEG artefact or one of regular contrast ....

Here's how it looked before being a silly Billy

 

[HoppyUK]

The problem looks to me like a case of the most unsympathetic sharpening I think I've ever seen. When you (or the camera) applies sharpening to an image it identifies boundaries (i.e. edges) between contrasting pixels and makes the dark pixels at the edge a little darker and the light pixels at the edge a little lighter. This creates the impression of a better defined edge, rather than one which might be a little fuzzy/soft.

If the effect here was simply one of excessive contrast then you would get very deep blacks and a pale sky, but not this odd halo at the boundary, unless as Hoppy says this is a JPEG artefact. The impression I get is not that this is a JPEG compressoion problem but sharpening gone absolutely nuts. You can't really see the blacks getting any blacker, because they are already so dark, but the halo in the sky is a huge clue (IMHO) that sharpening has gone way OTT in "enhancing", if I dare call it that, the contrast in the paler tone at the edge. Has this image been double sharpened or is that really what the camera is spewing out? To determine if it is a sharpening problem simply reduce sharpening as much as possible in the camera and then see how things look.

Just my two cents.

<snip>

That's what I meant Tim. A JPEG processing/sharpening thing. Maybe artifact is strictly speaking the wrong word.

Some careful custom processing would surely improve it but I don't think it's that untypical of what comes straight out of this type of camera. Unusual to be so crudely applied and unlucky to see it so blatantly perhaps, but not actually a fault as such.

 

[acs]

Here's an explanation of what appears to be happening: http://www.cambridgeincolour.com/tutorials/unsharp-mask.htm

-- in addition to the compression.

 

[tdodd]

Richard, I think the word "artefact/artifact" is fine. That is what it is. I just don't think the problem is down to the conversion to JPEG. It looks 100% like a sharpening artefact. When I pulled that crazy stunt in Lightroom the artefact was plainly visible on screen, long before converting and exporting the image as a JPEG.

Maybe I'm being pedantic (I actually think not) but I'm sure the problem is excessive sharpening and it really has nothing whatsoever to do with the conversion in camera to JPEG. The way to test my theory - lower the sharpening in camera. If the problem reduces then sharpening is the culprit. JPEG artefacts are more usually block/blotchy/tizzy effects, due to overcompression - chucking useful image data away. This effect does not look like a JPEG conversion problem to me.

Here is a 100% crop from my five year old Sony 7.2MP compact camera, including a variety of contrasty edges. The image looks pretty darned sharp, especially for a 100% crop, and yet is almost entirely devoid of unpleasant sharpening artefacts. The worst sign is probably under the chin of the lady in the background, but even then it is extremely minor and would vanish at anything less than 100% viewing.

Actually, given the magnitude of the problem in the first post I'm wondering whether that is a 100% crop or maybe a 400% crop. I just don't see how the halos could have become so huge without a serious error of judgement on somebody's part.

 

[acs]

This effect does not look like a JPEG conversion problem to me.

Not in itself though you can clearly see the impact of compression in the image.

I would look at that contrast setting.

 

[HoppyUK]

Richard, I think the word "artefact/artifact" is fine. That is what it is. I just don't think the problem is down to the conversion to JPEG. It looks 100% like a sharpening artefact. When I pulled that crazy stunt in Lightroom the artefact was plainly visible on screen, long before converting and exporting the image as a JPEG.

Maybe I'm being pedantic (I actually think not) but I'm sure the problem is excessive sharpening and it really has nothing whatsoever to do with the conversion in camera to JPEG...

<snip>

No, not pedantic at all Tim (though pedantic on matters of fact is also fine by me ).

I'm just being loose with my terminolgy and lumping togther the file compression aspects which strictly speaking is all that JPEGing does (and I agree is not the issue here) with the other aspects of image enhancement that are conduced simultaneously in the production of a 'JPEG' output. The procedure is of course more correctly a two stage business - a JPEG compression stage, plus a separate enhancement stage (sharpening, contrast etc) which is the problem I think.

Cheers

 

[Chaz Photos]

The problem looks to me like a case of the most unsympathetic sharpening I think I've ever seen. When you (or the camera) applies sharpening to an image it identifies boundaries (i.e. edges) between contrasting pixels and makes the dark pixels at the edge a little darker and the light pixels at the edge a little lighter. This creates the impression of a better defined edge, rather than one which might be a little fuzzy/soft.

If the effect here was simply one of excessive contrast then you would get very deep blacks and a pale sky, but not this odd halo at the boundary, unless as Hoppy says this is a JPEG artefact. The impression I get is not that this is a JPEG compressoion problem but sharpening gone absolutely nuts. You can't really see the blacks getting any blacker, because they are already so dark, but the halo in the sky is a huge clue (IMHO) that sharpening has gone way OTT in "enhancing", if I dare call it that, the contrast in the paler tone at the edge. Has this image been double sharpened or is that really what the camera is spewing out? To determine if it is a sharpening problem simply reduce sharpening as much as possible in the camera and then see how things look.

Just my two cents.

EDIT : p.s. here's a 100% crop from one of my images, which was absolutely fine until I added maximum sharpening in Lightroom, and now looks equally sh!tty. OK, my ham fisted effort is perhaps even worse, but you get the idea - this is a sharpening halo, not a JPEG artefact or one of regular contrast ....

Here's how it looked before being a silly Billy

 

[hillwalkinggirl]

Barbara, the way compact sensors are described is weird and dates back to some old TV tube standards that take a bit of getting your head around. Here's an explanation from DPReview http://www.dpreview.com/learn/?/Glossary/Camera_System/sensor_sizes_01.htm

The diagonal of your "2.33in" sensor is 11mm, 8.8 x 6.6mm. So the area we're looking at in your OP enlargement is about the size of a pin head!

What I'm saying about the post processing bit is with the frankly miniscule amount of image data the camera has to work with (forget 12m pixels or whatever, that's just marketing) the JPEG engine gives the image a serious makeover to try and make it look half decent - basically a digital airbrushing. Among the many things it does is try to create artificial lines between areas of light/dark tone to enhance the impression of sharpness and that's what you're seeing.

To be fair, that's the basis of most sharpening procedures and all digital images need at least some of that, but compacts just need a lot more of it. What they do to noise is even worse, smearing away a lot of detail to conceal the noise, then trying to pull back the lost sharpness with more of these edge enhancement procedures.

And with respect to your Leica lens, which I strongly suspect has got nothing more to do with Leica than the name, will also be benefiting from distortion control in the JPEG engine, vignetting reduction, and the digital reduction of CA. Frankly it's not possible to produce lenses with the range of your 25-300mm equivalent zoom without a great deal of digital processing help going on behind the scenes. Manufacturers don't like to talk about this much and prefer to pretend that it's all down to their wonderful lenses, but if you could get a naked Raw file out of your camera you would see the reality of what's actually recorded by the sensor as original data, and it wouldn't be pretty.

Not dissing your camera or even compacts in general, but they have their limitations and looking at 100% images is going to reveal them. Pixel peeping is bad for your health

Thank you Richard, that explanation helped a lot.

 

[hillwalkinggirl]

I see looking at that exif data Barabara that contrast is set at +21. I don't know how that equates to the default settings, but increased contrast might cause this fringing.

It can also be induced in processing by over-sharpening and the use of feathered masks can often leave this type of halo

Hi CT, I've just taken another test photo set at landscape and the contrast is at normal. Strange things are happening. I've just done a reset on my camera now.

 

[hillwalkinggirl]

The problem looks to me like a case of the most unsympathetic sharpening I think I've ever seen. When you (or the camera) applies sharpening to an image it identifies boundaries (i.e. edges) between contrasting pixels and makes the dark pixels at the edge a little darker and the light pixels at the edge a little lighter. This creates the impression of a better defined edge, rather than one which might be a little fuzzy/soft.

If the effect here was simply one of excessive contrast then you would get very deep blacks and a pale sky, but not this odd halo at the boundary, unless as Hoppy says this is a JPEG artefact. The impression I get is not that this is a JPEG compressoion problem but sharpening gone absolutely nuts. You can't really see the blacks getting any blacker, because they are already so dark, but the halo in the sky is a huge clue (IMHO) that sharpening has gone way OTT in "enhancing", if I dare call it that, the contrast in the paler tone at the edge. Has this image been double sharpened or is that really what the camera is spewing out? To determine if it is a sharpening problem simply reduce sharpening as much as possible in the camera and then see how things look.

Just my two cents.

EDIT : p.s. here's a 100% crop from one of my images, which was absolutely fine until I added maximum sharpening in Lightroom, and now looks equally sh!tty. OK, my ham fisted effort is perhaps even worse, but you get the idea - this is a sharpening halo, not a JPEG artefact or one of regular contrast ....

Here's how it looked before being a silly Billy

No I haven't sharpened the image at all, that's how the camera spewed it out. There is a picture adjust option in the menu which can be applied when using Aperture, Shutter of manual mode. I am going to try taking some pics with the sharpening at a negative value to see what happens. I agree it definately looks like a sharpening halo.