3 steps to fix a blue sky using the Skin Tone tool

Capture One Pro 9 has a number of tools designed for working with images captured using a Technical Camera System. The Skin Tone tool in the Color Editor, however, is not one of them. This Tool is actually designed for improving the render of skin tones, ensuring that the skin is clean, smooth and pleasing. Surprisingly this tool also works extremely well for fixing variations in tone of a blue sky captured with a Technical Camera System.

The above image has been captured using an ALPA Technical Camera equipped with a Rodenstock ALPA HR Alpar 4.0/35mm lens and a Phase One IQ3 digital back.  To avoid converging vertical lines in the building and to preserve all the details the camera system provides, I have shifted the lens up 8 mm while maintaining the camera is horizontally straight and perfectly level.

This lens may not be specifically designed for movements when paired with a Full Frame 6×45 image sensor, as you find in the IQ3 digital back. However when the lens is stopped down to f/11 you find  the best compromise between depth of field and,  you can then get away with movements of approximately 8-9 mm without losing your image in the corners.

Tip902 Img2 full

Image on the left is a capture directly out of the camera.  It shows large color variations in the sky caused by the wide-angle technical camera lens.  The image on the right is the same image processed using Capture One Pro 9 and applying the tools for technical cameras as well as the Skin Tone Tool.

To achieve perfect color render in images like the above, taken on a technical camera, the three steps below are required in addition to capturing the image:

1) Capture a Lens Cast Correction (LCC) reference image

2) Correction for Lens Cast (LCC)

3) Fixing minor color issues


1. Creating a LCC reference file

For Capture One Pro 9 to compensate for the strong color variations seen in the sky, a separate image of a translucent white reference plate needs to be captured.

Tip902 Img3 full

Without changing the movements of the camera or the aperture, hold the translucent plate directly infront of the lens and make a capture. Typically you’ll need to change the exposure time equivalent to 2 f-stops to get a good exposure.

2) Correcting for Lens Cast

Lenses for Technical Cameras Systems take advantage of the fact that there’s no need for the mirror box which facilitates a normal camera’s prism, and therefore the lens can get much closer to the sensor.  This is is a great advantage when designing a wide-angle lens as it allows them to be smaller and optically superior.  However, with the lens so close to the sensor there is a significant challenge with the angle of incident light reaching a pixel.  The angle of incident light can be quite extreme and exceed the normal range that the micro-lenses of each pixel are designed to accommodate.

In Capture One Pro 9 select the LCC reference file of the translucent white plate. From within the LCC tool in the Lens Tool tab, click “Create LCC”.

Tip902 Img4 full

Straight out of the camera the images of the translucent white plate show color variations as well as light fall-off.

Tip902 Img5 full

 

When you create the LCC make sure to tick the box for Dust Removal Information, as this will allow you to automatically fix minor dust spots in your final image.

Also tick the box for “Wide Angle Lens with Movements” as this will initiate additional calibration data needed for images taken with wide-angle lenses that include movements.

After the LCC calibration has been created, it is automatically applied to the selected image in order to verify the correction actually will be able to correct the image.

Tip902 Img6 full

With all boxes checked the LCC reference image now shows a perfect grey image without color cast, dust spots or light fall-off.

Tip902 Img7 full

To apply the LCC calibration information to the desired image, you simply select both the LCC reference image and the image of the building.  Once selected, right-click on your desired file and from the menu options select “Apply LCC”.

The task of creating and applying LCC files can be done on multiple LCC files, just select all the translucent white reference files and select “Create LCC” from either the LCC Tool or from the right-click menu in the thumbnail browser.  If all your images are organized by a number of exposures followed by a LCC reference image, followed by exposures and then  LCC shots (and so on), you can properly batch-apply the LCC calibration information. Simply select all the images including the LCC reference image and select “Apply LCC” from the right-click menu in the Thumbnail browser.

Tip902 Img8 full

With the LCC calibration information applied to the image, it immediately looks much better.  The calibration has reduced most of the colorcast in the image but as I have applied movements to the lens, causing an steeper angle for the incident light on the sensor, the LCC calibration doesn’t fix the color variations perfectly.

3) Fixing the remaining color variation using the Skin Tone tool

To fix the blue sky I will be using the Skin Tone tool in the Color Editor.  I could work on the whole image but as there are quite a bit of blue tones in the building I would rather work in a Local Adjustment mask, created from a color selection in the Color Editor. Doing so, I can modify the mask to only include the sky.

From the advanced tab I make a color pick on the blue sky.  I click on the “View Selected Color Range” to verify that I’ve got the right selection.
Tip902 Img9 full

Now when I know I have the right color range selected I can convert this selection to a Local Adjustments Mask.  I do so by clicking on the three dots (tool options) in the Color Editor Menu line and select “Create Masked Layer from Selection”.

Tip902 Img10 full

In the Local Adjustments Tool tab I can finally move into the Skin Tone tab in the Color Editor.

This tool is designed for improving skin tones using the Uniformity sliders; these are designed to even out differences in a subject’s skin.  It’s a very specialized tool for specific use, however these sliders also work perfectly on the blue sky of this image.  In this example I adjusted the Uniformity of the Hue to 100%, Saturation to 67% and Lightness just a tiny bit. This adjustment totally eliminates any color variation in the sky.

With the Adjustment sliders I can further tweak the color tone to my desired blue tone.

 

All the best,

Niels

May 12 2016

By The Image Quality Professor

Category: Professor Tips Tags:
  • Download Capture One Pro 10 Now

    The download contains a free 30-day trial with all features unlocked. Capture One Pro 10 is a PAID upgrade from Capture One Pro 8 or 9.

  • Book a demo

    Get a demo of the full XF Camera System, high resolution lenses and digital backs. Sign up now, and our local partners will get in touch with you very soon.

  • The Image Quality Professor
    The Image Quality Professor

    The digital pioneer, Niels V. Knudsen, is Phase One’s Image Quality Professor and founder of the IQP blog. Moreover, he is responsible for breakthrough advancements in image quality both in Phase One’s medium format camera systems and in Capture One Pro.

    Share this article

    Follow by Email
    Facebook
    Twitter
    LinkedIn

    Comments (20)

    Thanks Niels. Always look forward to all the tips and tricks that come my way. Almost four years now as a lover of CO. Wonderful software that makes me looks so good, so easily! Keep doing what you do so well :)

    The Image Quality Professor

    Hi Dave,

    Thanks a lot for your kind words. We are so happy to hear that you enjoy working with Capture One.

    All the best,
    Niels

    I don’t see a need to create a mask from the colour selection.

    The uniformity adjustment only applies to the targeted colours anyhow. In your example, the targeted pixels are identical to the masked ones.

    A good reason to create a mask is to have the ability to exclude certain areas from correction (e.g., people wearing jeans or similar) by erasing the mask from those areas.

    David Grover

    There are similar blue tones in the building. Therefore after creating the mask, it can be edited to remove those building parts.

    As Niels said.

    David

    johnb263

    HI Niels – I’m following just step3 in your method to get sky uniformity (due to local contrast adaption) – so, I use the global color editor, select the sky color, create a mask, erase the parts of the mask that I do not want to adjust, go to color editor / skin tones in the local adjustments tab, and try to adjust uniformity. I’m expecting the mask to apply, so only areas below the mask will adjust – but, the whole image adjusts.. Missing something?
    John

    John,

    Does the Advanced Colour Editor tool you are using display a little brush icon (as used by the masking enabled setting) next to the name?

    If NOT the tool is set to be working with the Background not the layer.

    If it does have that icon but still affects the whole image despite your modified mask then something strange is happening – difficult to advise without actually seeing what you are seeing.

    johnb263

    Grant, thanks – yes, I am using the color editor in the local adjustments tab – so it’s got a little brush next to it. I thought the latest update will fix the problem – still the same. The difference is what was also mentioned by Richard Allen – inside the local adjustments tool one needs to re-select the color you want to adjust (otherwise all the controls are greyed out). I think this is the problem – this selection is not affected by the mask – it looks at the whole image. I also made sure the mask that I created was selected in the “local adjusments” drop down. so, I still don’t see this working (although I really would like to..) Attaching a image I tested it with

    johnb263

    I don’t think this works as intended. The mask does not apply to local color adjustment. Would be nice if it did, though..

    The Image Quality Professor

    Hi John,

    Creating a mask from the Color Editor, gives you the option to use the mask for anything you would like to. In this particular case it happens to be that I would like to unify the color variation. You could have used the mask for another purpose.

    All the best,
    Niels

    The Image Quality Professor

    And for Skin Tone correction, you may want to use negative clarity for evening out skin tone imperfections.

    Laurin Rinder

    shooting 55+ years. Im sorry But what happened to shooting it correctly in camera instead of fixing or fiddling yourself to death in software. Most of you guys if had to shoot film and nail It would be out of work. Sorry..

    Enough is enough. whats next software to shoot it for you???

    David Grover

    Hi Laurin,

    The corrections Niels is making is simply not possible ‘in camera’. The observed colour shifts is a by product of very wide angle lenses on high resolution sensors. There is no way to correct for this at time of Capture.

    Fortunately as Niels demonstrated, its easy to do it within Capture One.

    David

    Laurin – which film stock, camera and lens system would you use to avoid any problems in that shot?

    Would you consider undertaking any corrections in the dark room?

    Or maybe, as per the old days, print the result in monochrome then have it hand coloured if that was want the client wanted?

    I think the point here is that digital technology is not without limitations and presents its own challenges which are different to those of film. As are the answers to the challenges and the use of a “digital darkroom”.

    I am fairly sure I could not afford to shoot film these days.

    Richard Allen

    Once I have used the “Create Masked Layer from Selection” if I then go to the ‘Skin Tone’ tab there is no adjustment for me to make as the settings are all greyed out?

    The Image Quality Professor

    Hi Richard,

    Thanks for your question. See the reply above.

    All the best,
    Niels

    George Norkus

    Hello Niels,

    Here are two questions which I’m quessing the LCC might be an answer to my problem.

    In the fall I photograph high school football games. Most of the high schools do not have an electrical cycle balance. When I photograph the plays at 1/800 or 1/1000sec, some end up with a reddish cast to all or a portion of the photograph. I believe the reason is because the speed of the shutter catches the light sort-of “blinking”. (I get random reddish cast on photos taken within seconds of each other. Some appear normal, some have a partial reddish cast, and some complete.)

    Being I cannot replicate this reddish cast until a future night game, (fall time), do you or someone else think the use of an LCC would correct for it?

    Also, am I correct in thinking it is caused because of the cycle rate of the stadium lights?

    The Image Quality Professor

    Hi George,

    Sorry for the late reply. I agree, I think you are right about the cause of the reddish cast. That’s why a LCC won’t help you.

    I would suggest that you bring a grey card next time you shoot football games in the fall, and make a series of shots where you try to catch the same reddish cast of the grey card.

    All the best,
    Niels

    Hello Niels

    Can I use step 3 (skin tone tab) to get rid of a color cast?
    I’m into automotive and often I have a blue color cast on the windows of a car, etc…
    Or do I use the “advanced tab” and a mask to do this?

    Greetings
    Gerd

    David Grover

    Hey Gerd,

    I think using the Advanced tab with a Local Mask would be the best option.

    David

    Add a Comment

    ATTACH IMAGE