Posts Tagged ‘blending modes’

Feb
27
2010

The Myth of the Golden Hour, Part IV

The image above was recorded in The Wave at about 12:20 MST on August 27, 2009, using the Nikon D700 and the AF-S NIKKOR 24-70mm f/2.8G ED lens at 45mm.  Exposure was f/16 at 1/250s, with an ISO of 200.  The Wave is found in the Coyote Buttes North section of Vermilion Cliffs National Monument in Utah/Arizona.

In a previous installment in this series I’ve indicated that the contribution to image contrast of the individual red, green, and blue channels are unequal.  In fact, the green channel contributes twice as much as the red channel, and the red channel contributes three times as much as the blue channel.  There are quite natural reasons for this curious channel weighting, which we will consider in a future entry.  For the current consideration we will focus on how we can modify the apparent weighting of the contributions of the individual R, G, and B channels.

The book says that an image recorded at midday is likely to be weak, e.g., lacking color saturation and contrast.  Admittedly, perhaps the composition is a bit ordinary, but there is nothing lacking in the image above in terms of image contrast and color saturation.  On the other hand, and as is shown below, that is not how this image started out.

Well, this is obviously an overexposed image you might say.  Nope, check the histogram.

I bracketed this shot too, and this is the best compromise between overexposed and muddy.  The lack of contrast is a result of shooting the scene with the sun pretty much exactly overhead – what audacity!

We appear to have quite a way to go to bring the source image to the final image, but it’s actually quite straightforward.  Begin by reviewing the red, green and blue channels of the source image.  First copy the Background layer, (cntl>j (<cmd>j on the Mac) to generate a new layer (Layer 1).  Then select the red, green, and blue channel panels in turn in the CHANNELS palette.

As you can clearly see below, the green channel possesses much better contrast than the red channel – this channel is in pretty good shape.

The blue channel (below) has much better contrast than the red channel.

To enhance contrast in that weak red channel we simply replace the red channel (blend) with the blue channel.  To accomplish this replacement, we employ the Apply Image tool to execute the blend by first selecting the red channel, and then typing Image > Apply Image, and then specifying that the blue channel be added to the red channel in Normal blending mode at 100% opacity.  The result is shown below.

While you might be able to appreciate the contrast enhancement, the resulting influence on color dominates your impression.  We can restrict the influence of channel blending by changing the blending mode of the Background copy layer to Luminosity.  The result of the change in blending mode is shown below, with the original source image shown below that image for comparison.

This is a significant improvement.  The contrast is then further enhanced by applying a curves adjustment to the red and green channels (you could also apply a curve to the blue channel, the influence on the overall image contrast would be small).

To finish processing of the image we apply the image to itself in Multiply blending mode by first flattening the image, and then copying the resulting layer and changing the blending mode to Multiply.

Finally, we apply Shadow/Highlight adjustment to open up the mid tone range a bit: select Image > Adjustments > Shadow/Highlights…

I hope that you’ve found this entry useful.  If so, please drop me a line and let me know what you’d like to see in future posts.  Cheers, P.

Copyright 2010 Peter F. Flynn. No usage permitted without prior written consent. All rights reserved.

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Posted in Adventure, Methods, National Parks and Monuments | 5 Comments »

Jan
22
2010

The Myth of Golden Hour, Part II

The image we will consider in this entry is the often-photographed Horseshoe Bend site near Page, AZ.  The overlook is located about 6 miles south of Page on US 89, at the end of a 0.75 mile hike (one-way) over rolling sandy terrain.  The final processed image is shown below.

The source image (shown below) was was recorded on July 22, 2009, at about 14:40 MST, using the Nikon D700 and the AF-S NIKKOR 24-70mm f/2.8G ED lens at 27mm.  Exposure was f/16 and 1/125s, ISO 200.  Minimal processing of the RAW image was conducted during the conversion.

The image exhibits the anticipated washed-out attributes that we would anticipate given the time of day at which the image was recorded.  In this instance, as we so often find, photographing this amazing scene during the Golden Hour is simply not tractable, since long shadows would fill the canyon, generating an uninteresting image.  Our only option is to record the image when the sun is relatively close to its zenith, and hope to enhance detail and color post-capture.

Below, I include a screen capture of the ACR Raw conversion interface below to illustrate that although the image it pretty washed out, the histogram indicates that things aren’t too bad – this is common is images recorded near midday on sunny days.

There are several things would should like to improve.  The clouds on the horizon are attractive, but a bit blown out.  There is dramatic color variation, but it definitely could be much better.  Specifically, both contrast (luminosity) and color variation would be improved by both darkening the sandstone surfaces throughout the image and by expanding the subtle range of color present.

We’ll tackle the clouds/sky issue first.  We begin by copying the Background layer to generate the Background copy layer.

The next move is difficult to motivate, but the results are compelling.  Apply the blue channel of the RGB image to the R,G, and B channels in Normal blending mode – select  Image > Apply Image…   Note that the Invert box is checked – this is important.  See the dialog box and resulting image below.

Not yet clear where this is headed?  Try changing the blending mode of the Background copy layer from Normal to Overlay blending mode as shown below.

Although you may be able to see that we have increased definition in the clouds, the image still looks pretty strange., and specifically there is an odd loss of resolution throughout most of the image  We clear this up by blurring the Background copy Layer.  Make certain that the Background copy layer is selected (the layer icon will turn blue if you are using default settings).  Then select  Filter > Blur > Gaussian Blur…  The Gaussian Blur dialog box will appear, and allow you to vary the radius parameter.

The proper setting of radius depends on the resolution of the image.   As you increase radius, the image will gain back the original resolution of the source image, but the clouds – and – other highlight regions of the image – will have improved definition.  For this 12MP image, I had to apply the maximum value, 250 pixels, twice.  The Photoshop engineers definitely need to increased the range of the radius parameter to accommodate current and future image sizes.  The resulting image is shown below.

Careful comparison between the working image shown above and the original image indicates that the Overlay procedure has left the image much lighter.  We restore the original luminosity by first copying the Background image to generate a new layer named Background copy 2, and then draging that new layer to the top of the layers stack as shown below.

Of course, since the blending mode of the new layer is Normal, the view you now have of the image is exactly the same as when you started – placing any image with blending mode set to Normal  at the top of a layer stack simply displays that image.  Things get interesting when you convert the blending mode to Darken as shown below.

The influence of the processing becomes clear when we view a section of the sky as shown below – original image on the upper half.

Note that not only has the definition in the clouds improved, but the canyon walls have also been enhanced.  This is a good stopping point for the current entry.  Stay tuned for part III.

One final note.  I didn’t invent any of the methods discussed in this entry.  My approach is a combination of a wide range of influences, including ideas discussed by Martin Evening, Bruce Fraser, Scott Kelby, Dan Margulis, Deke McClelland, Jeff Schewe, Rov Sheppard, and a number of others – all of the folks listed by name publish excellent texts on image processing and are well worth owning.

An image of the Horseshoe Bend area is shown below courtesy of Google Earth Imaging.

Copyright 2010 Peter F. Flynn. No usage permitted without prior written consent. All rights reserved.

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Posted in Adventure, Methods | 2 Comments »

Jan
13
2010

The Myth of Golden Hour, Part I

The Golden Hour is a classic photographic nutshell that recommends that the best times for recording images are approximately the first hour after sunrise, and the first hour prior to sunset.  This concept is so neatly set in the minds of photographers that it has come to suggest that high quality images can only be recorded during the Golden Hour intervals.  The point of this series of entries is not so much to debunk the idea, as to provide a practical example of  the relatively facile and powerful modern digital processing methods.

We should first consider what it is about the Golden Hour that make this time so special for recording photographic images.  During the Golden Hour, the angle of the sun with respect to the horizon is small, certainly less than 15°, so that the light directly from the sun travels a greater distance though the atmosphere; which reduces its intensity, and also produces characteristically relatively long shadows.  Moreover, the relative contribution to the overall light intensity from the sky is enhanced.  This sky light is characteristically extremely diffuse, e.g., think of the sky as the ultimate light diffuser.  In terms of the color of the light, the longer path traveled by the light leads to a relative decrease in the blue component due to dispersion, leaving a relative enrichment in yellow and red components.

On the day that the image shown above was recorded, August 28, 2009, sunrise occurred at approximately 06:50 MST.   The image was recorded at 10:45 MST, well outside of the Golden Hour, and exhibits the overwhelming highlights and deep harsh shadows that are characteristic of images recorded near mid-day.  The image was recorded using the Nikon D700 and the AF-S NIKKOR 24-70mm f/2.8G ED lens at 44mm.  Exposure was f/16 at 1/125s, ISO at 200.

The image is pretty washed-out/over-exposed.  Although we might have been able to do more with an exposure at -0.67 EV, there is little doubt that this image would most probably be more appealing, at least in the classic photographic sense, if it had been recorded between 19:00 and 20:00, since sunset on this date occurred at 20:00 (the image was recorded looking westward, e.g., into the rising sun, not a tractable shooting scenario).  The problem was, as it often is, that I wasn’t there during the Golden Hour!  Moreover, obviously most life occurs at sometime other than during the Golden Hour.  Is there anything we can do to add more pleasing contrast and color saturation to such images?  I certainly think so, otherwise I would have written this entry!

Let’s begin with a simple fix, which is to add a new layer on top of the original layer, and change the blending mode of the new layer to ‘Multiply’.  Begin by dragging the Background layer to the copy layer icon, thus generating the Background copy layer as shown below:

Now change the ‘blending mode’ of the Background copy layer to Multiply as shown below – note that the pull-down menu tab contains a number of blending options – select the downward pointing arrow to the right of ‘Normal’ underneath the Layers tab to reveal them.

The result is shown below.  I’d suggest that there may be no simple move that produces such a dramatically improved result as the addition of a Multiply-layer to a washed-out or overexposed image:

Finally, we can vary the extent of the blending of the top layer into the bottom layer by adjusting the opacity of the top layer.

I hope that you have found this entry to be useful.  Good luck on your own efforts.  Keep shooting, and don’t believe ’em if they tell you you can’t make solid scenic color images outside of the Golden Hour.

Copyright 2010 Peter F. Flynn. No usage permitted without prior written consent. All rights reserved.

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Posted in Methods, National Parks and Monuments | 5 Comments »

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