Sunday, July 05, 2020

Does software level the playing field? [2]

I previously shared my thoughts that, yes, software and the "capture sharpen" function in particular, can indeed "level the playing field" in terms of "sharpness" in an image, independent of which lens is used.

Before moving on to see how this compares and works in the real world I would like to confirm what I have come to understand by looking at three more lenses

In this comparison I look at two Nikon Nikkor 85mm lenses with a LensTurboII focal reducer and one Sony 50mm SEL OSS.  These lenses were commonly touted as being good "portrait" lenses.  In fact, the Nikkor K 85mm f/1.8 is a gorgeous "portrait" lens.  It is not as wickedly sharp as some of my other lenses when shot wide open, but the overall wide open rendition, I find, is just amazing.

Setup -

  • Big Beefy Manfrotto tripod (so big that it is suitable for stabilizing an old 8x10inch view camera)
  • Sony NEX-7 - 2 second delay, ISO 100
  • Lenses - shot wide open and at f/2.8 only
    • Sony 50mm f/1.8 SEL OSS - effective full frame focal length of 75mm
    • Nikon Nikkor 85mm f/1.8 K pre-Ai + Lens Turbo II - effective APS-C focal length of 56mm
    • Nikon Nikkor 85mm f/2 Ai + Lens Turbo II - effective APS-C focal length of 56mm

Scene -

What I setup was a simple situation of a tree that had complex, beautifully detailed bark.

Sony 50mm, Nikkor 85mm Capture Sharpen Comparison


Comparison -

Click on the following image and find the full resolution image to inspect the image at 100percent.

Sony 50mm, Nikkor 85mm Capture Sharpen Comparison


Comments -


In general, "soft" or out of focus image areas will remain so after passing the "capture sharpen" step.

I have to say, I'm particularly happy to see how well the Sony 50mm f/1.8 SEL OSS did from wide open.  As we will see in a future blog entry, I had a Sigma 60mm f/2.8 Art that I nearly regretted selling, until I saw this, that is.  In any event, this Sony lens is truly the "cat's meow" of a lens and it's a "keeper."

The Nikon Nikkor 85mm f/2 Ai + LensTurboII focal reducer is really quite nice from wide open, too.  It isn't all that far behind the incredible Sony.  With this I think I can re-confirm that the "capture sharpen" function "levels the playing field" rather nicely.  This old Nikkor is a very usable optic.

Finally, the Nikon Nikkor 85mm f/1.8 K pre-Ai + LensTurboII focal reducer remains softer than the other two lenses when shot wide open.  Not that the wide open "capture sharpened" image is bad, mind you.  It's only by comparison that one can see any difference.  However, by f/2.8, the "playing field has been leveled" and this early f/1.8 Nikkor is just as brilliant as it's sister lenses compared here.

Do lenses actually matter?  It's turning out to feel as if it might not matter at all which lens you use, just as long as you "sharpen" an image correctly during processing.

Now there's some potential heresy for you.

Friday, July 03, 2020

Does software image processing "level the playing field?"

We were in in southern France this winter and taken the TGV.  This allowed me to pack a rather heavy suitcase.  But coming back north meant flying.  Suddenly the suitcase was a bit heavy.  My wife tried to pick up my carry-on and immediately asked what the h*ll I had in there.  It contained two computers and three cameras with Nikon Nikkor manual focus lenses.

My wife's question was a good one and I've now come to question that I should carry all my fun, preferred "stuff" when we're away from Paris.  Instead I might want to carry something light.

So... let's have a look around and see what I have... ah... yes... Sony E-mount autofocus lenses... and... some software... and... why not once more and without hesitation confirm that a lens is a lens is a lens... and... let's have a look at the impact of image processing on image "sharpness" to see if any differences between lenses remain after cleaning up an image with some software...

Recently RawTherapee has come bundled with something called "Capture Sharpen".  It is an image pre-sharpen module that works to reverse image softness that comes from imaging sensors that use anti-aliasing (AA) filters. 

This function is automatically applied, I understand, in popular non-open source software image processing applications such as Lightroom and Capture One.   

This makes sense as, for instance, Canon uses strong AA filters with their cameras to combat moire patterns.  This tends to hide optical resolution.  Canon digital images often appear softer before the "capture sharpen" image processing step than competitors imaging systems.

Sony is one of those competitors and based on personal experience they use weaker AA filters, and in some cases uses no AA filtration at all.  So it's easy to see lenses of varying degrees of "sharpness", particularly when shot wide open.

So I wondered if "capture sharpen" might clean up optical effects similarly to the way this function tries to reverse the effects of AA filters.

In this comparison I grabbed some of my beloved Nikon Nikkor glass (which tend to be soft wide open) and compared their images against a few small, sharp, auto-focus Sigma and Sony SEL lenses.

Setup -

  • Big Beefy Manfrotto tripod (so big that it is suitable for stabilizing an old 8x10inch view camera)
  • Sony NEX-7 - 2 second delay, ISO 100
  • Lenses - shot wide open and at f/8 only
    • Nikon Nikkor 24mm f/2.8 Ai + Lens Turbo II - effective APS-C focal length of 16mm
    • Sony 16mm f/2.8 SEL
    • Sigma 19mm f/2.8 EX DN E
    • Sigma 30mm f/2.8 EX DN E
    • Nikon Nikkor 35mm f/2 + Lens Turbo II - effective APS-C focale length of 35mm

Scene -

What I setup was a high contrast situation with strong highlights and deep shadows.

Sigma 30mm f/2.8 EX DN E scene setup


Comparison -

Click on the following image and find the full resolution image to inspect the image at 100percent.

Nikon Sony Sigma "Real World" Comparison


Comments -


In general, "soft" or out of focus image areas will remain so after passing the "capture sharpen" step.

Comparing my Nikon Nikkor 24mm + LensTurboII setup against a Sony 16mm after the "capture sharpening" step I see that the centers are pretty much equal in terms of apparent sharpness.  The edges, however, of the 24mm + LensTurboII remain softer than the 16mm Sony.  In fact, at f/8 the 16mm Sony is really quite good, where it matches the performance of the brilliant 19mm Sigma EX DN E.

The Sigma 19mm and 30mm lenses are brilliant across the field at both wide open and f/8 after the "capture sharpen" step.  Not much more to say than this.

Which leaves us with looking at one last Nikkor, the 35mm f/2 pre-Ai.  I really like this lens.  When coupled with the LensTurboII focal reducer I find this focal length is nearly a perfect match for how I "see."  Wide open it tends to be just slightly "soft" compared to the Sigma 30mm.  However, after the "capture sharpen" step apparent "sharpness" the Nikkor cleans up beautifully.

Old, many times softer lenses can be made to look like their modern counterparts.  It's pretty easy to see that "capture sharpen" levels the playing field, as it were.

Returning to the question of camera system weight and portability, I'm now re(?)-convinced that I don't have to carry the Nikon Nikkors if I don't want to or if I find myself in a situation where less weight becomes important.

Friday, June 26, 2020

Super Selective toning ~ finale

I've taken three steps (step one, step two, step three) to reach this level of understanding around what is possible with selective toning of black and white images using Open Source Software image processing applications.

In this, the fourth and for now final step in my process of understanding I look at preserving as much image information as possible as the means to keeping  histogram as smooth as possible.

As you will recall, when processing jpg images there are only 256 luminosity steps.  Any changes made to the image quickly introduces gaps/spikes in the histogram.  This indicates lost information. 

Most of the time this is beyond the ability of the untrained human eye to perceive.  But, to me at least, this is intellectually unsatisfactory.  More practically there are many cases where we would like to preserve as much information as possible when we make any changes (strong or otherwise) to an image in processing.

For these reasons I turned my attention to using the image toning functions in RawTherapee.

This Open Source Software application handles a vast array of RAW formats and provides 16bit image color spaces as default, with the possibility of dealing with 32bit floating point color spaces, too.

Limiting our attention to three functions we will see how easy it is to selectively tone an image while keeping the histogram very smooth.

Step One - Open a RAW format image in RawTherapee

In this example I pressed the "Auto Levels" button and let the application sort out how to arrange the image tones automagically. 

Then I opened "Tone curve 1" and snugged up the blacks and raised the whites in anticipation of emulating old silver halide prints.

RawTherapee black and white image toning


Step Two - Convert to black and white (I like "luminosity" conversions, but you may prefer something different, like de-saturation or RGB conversions).

RawTherapee black and white image toning


Step Three - Tone the image using "Color Toning"

Example A

RawTherapee black and white image toning

Note the settings I used.

The highlights remain neutral in this example.  So specular highlights in the image will remain pure white.

The mid-tones in this example are strongly Yellow, with a hint of Red and Green.

The shadow tones are just slightly blue to emulate a cool tone shade that we experience in nature (the color temperature of shadows are typically must lower than the color temperatures of highlights).



Example B
RawTherapee black and white image toning

Note the settings I used.

The highlights again remain neutral in this example.  So specular highlights in the image will remain pure white.

The mid-tones, however, are now slightly Yellow, with a hint of Red and, in this example, Magenta.

The shadow tones are stronger blue than the first example to more strongly emulate a cool tone shade that we experience in nature (again, the color temperature of shadows are typically must lower than the color temperatures of highlights).

Comments -

In your own work, I would suggest opening a toned image that appeals to you in a separate window.  Then work on your RawTherapee image toning sliders until you match the tones of your favorite toned image(s). 

If you save these settings you can then quickly recall them to be applied to any image.  RawTherapee has a good set of instructions on how to do this.

Monday, June 22, 2020

Super Selective toning in the Gimp ~ Part Three

In a prior blog entry I described a means of using the Gimp to tone the mid-range of a black and white photograph while keeping the blacks black and the whites white using Luminosity Masks.

This can be a rather complex process.  We will now try to dramatically simplify the entire toning procedure.  At the end of this post we will have a look as to whether this is a satisfying answer.  So stay tuned.


Setup -

Processing -

I will give a very specific set of instructions here.  However, keep in mind there are many combinations and variations that might help you express your intentions better.


Step One -

Open a black and white step wedge in the Gimp



the Gimp ~ converting gray scale with subtle tones

Now open three previously sample colorized step wedges.  Open cool tone wedge and two warmtone color wedges.  We will use this starting in Step Four.



Step Two -

Create 9 Luminosity Layers and Masks with one click

Select Filters -> Generic - Luminosity mask setup and watch as new masked layers are generated. 

Note how they are arranged with the "Darks" layer set of three grouped layers labled "DDD", "DD", and "D".  Similarly, note how the "Mids" and "Lights" are organized.  We are about to rearrange them.

But before we do, take a close look at how each set of three sub-layer masks are slightly different from one another.  They define how much of a region will be affected when we make changes to the layer image. 

Said another way, each mask uniquely describes what portion of the image will be affected by any changes we make to each layer image that each mask is attached to.


the Gimp ~ converting gray scale with subtle tones


Step Three -

Re-Ordering the Luminosity Mask Layers.

When we add color to these Luminosity layers, their arrangement and order will be important.  How the colors will blend and transition between the layers will be determined by the order you choose. 

We will now rearrange them to prepare for sample colorizing.

Click on the "Mids" top of group layer (where the "MMM", "MM", "M" sub-layers are organized just below it) and select the up arrow carrot.  When you click on the up arrow carrot after selecting "Mids", the entire "Mids" layer structure will move.  The up arrow carrot is found on a tool bar just below the base image.  Verify that "Mids" collection of three layers and masks are now positioned above the "Darks" collection of three layers.

Click on the "Mids" "M" layer and move it above the "MMM" layer (as seen in the example below.

Now click on the "Lights" collection of three layers and masks and again using the up arrow carrot click twice to move "Lights" first above "Darks" and then above "Mids".  "Darks" will now be the first Luminosity layer collection above the base image.  We have simply reversed the order of the layers and their masks.

There is one final task before moving onto the next step.  Deselect the "LL", "L", "MM", "DDD", and "D" layers. Your layers and masks should now look like the following.

the Gimp ~ converting gray scale with subtle tones


Step Four -

Select the "DD" layer image (not the mask - you can't colorize a mask).

Open Filters -> Map -> Sample Colorize and in the "Sample" pull-down menu select the cool tone step wedge.

Select Get Sample Colors

Select Apply

Select Close

the Gimp ~ converting gray scale with subtle tones



Step Five -

Adding a Mid-Tone Color select the "MMM" layer image (not the mask - you can't colorize a mask).

Open Filters -> Map -> Sample Colorize and in the "Sample" pull-down menu select a mid-tone sample colorized stepwedge.

Select Get Sample Colors

Select Apply

Select Close

the Gimp ~ converting gray scale with subtle tones



Step Six -

Adding a hint of color over the "MMM" layer by using the second warmtone stepwedge.

Select the "M" layer image (not the mask - you can't colorize a mask).

Open Filters -> Map -> Sample Colorize and in the "Sample" pull-down menu select the second of your two mid-tone sample colorized stepwedges.

Select Get Sample Colors

Select Apply

Select Close

the Gimp ~ converting gray scale with subtle tones


Step Seven  -

File -> Export the newly tri-tinted step wedge saving it using a meaningful name so you can easily identify and retrieve it in the future to tone your images.

From now on, all you have to do is open your image and open the step wedge in the Gimp and to sample colorize your image using that step wedge.  No need to use luminosity masking to get the detailed color tints you want.

Simple.


Summary -

You may have noticed that we have done nothing with any of the "Lights" layers.  Because of the way we ordered the layer stack, these keep the whites from the base image and will keep the whites white in final saved tri-toned step wedge.  In this example the "LLL" layer has the narrowest band of white of the three "Lights" layers.  By selecting other "Lights" layers you can extend the white and light grays further down the step wedge.

All you need to do is create one of these altered step wedges and you can consistently apply this exact range of tints to any image by sample colorizing using the newly created wedge.

However, let's think this a bit deeper. 

In 8 bit JPG images we have four channels to work with.  We have red, green, blue, and a black and white channel.  In converting to black and white we end up with only _one_ channel's worth of information, the black and white channel.  So when we add color _back_ to the black and white channel we have only 256 shades of gray to work with, even though we are adding color to the RGB channels.

What we've done is gone from an 8bit by 3 color channel color space down to just 256 bits of information to work with.  Most of the time the human eye can accept this and may find an image pleasing.

Looking at four channel curves in an image processing software reveals the fragility of using this limited amount of information.  This is readily seen when the "curves" are modified.  We can see in a histogram that information is at various points quickly lost.

I know.  Deep subject.  Is it worth all this thrashing?  I think so.  Here's why.

There might well be a very nice solution where we can easily work the black and white channel in a 14 or 16 bit RGB color space.  This has the promise of giving us a much smoother histogram "curve" and might help us experience images in a rich and, dare I say, gorgeous large format film nearly analog "look" and "feel" kind of way.

Onward to Part Four.


Sunday, May 31, 2020

Super Selective Toning in the Gimp - Part Two

Continuing the search for subtle toning based on selective tone ranges, here is a second method a person can use in the Gimp.

In Part One I laid out a process for selecting unique colors for selected Luminosity Mask regions.

In this, Part Two, I would like to share a process for using a unique feature found in the Gimp.

Under Colors -> Map at the end of the drop-down list is something called "Sample Colorize".  When used with a step wedge you can specify a range of colors that spread from pure black to pure white that apply tints to an image.  In analog photography terms you can think of this as a sophisticated toning mechanism.

There used to be a collection of step wedges you could download to work from, but I can't seem to find them anymore (it's been a number of years).  So I create my own step wedges from tinted images with color ranges that I like.  I tend to work from scanned carbon tissue, or platinum-palladium, or chocolate toned images.  I also have step wedges I created from scanned cool tone silver gelatin prints (I used to be a black and white photo print tech back when dinosaurs roamed the earth and still have some of my earlier works).

Looking at these step wedges you may quickly realize the subtleties in colors that are possible.  Here-in lay the promise for even finer tonal gradations when combined with the Luminosity Mask technique previously described.

I can't stress enough that there are any number of valid ways of achieving these kinds of results.  I am simply following a process path that seems obvious to me.  You mileage will vary (as they say).


Step Three - Get your step wedges ready

Continuing in the Gimp, open three step wedges.  I would suggest a cool tone wedge, a chocolate tone wedge, and a yellow-ish tone wedge.  These will open as separate files next to your base image tab.

Step Four - Cool down the shadow/dark tones

Return to the image to be toned and make the "DD", "MMM", and "LLL" layers the only _active_ (visible) Luminosity Mask layers.  We won't need the other masked layers so we need to make sure they are de-activated.

Working with your base image, select (for this example) the "DD" layer image (not the mask as you can not Sample Colorize masks).

Open Colors -> Map -> Sample Colorize

In the upper right corner of the dialog box, find and select the cool tone step wedge. 

"X" use subcolors ("smooth colors" should already be selected just to the right)

Select "Get Sample Colors"

Select "Apply"

Select "Close"

You should now see the image you are working on has taken on the cool tones of the step wedge in the dark regions.

Step Five - Warm up the middle tones

Select (for this example) the "MMM" layer image (not the mask as you can not Sample Colorize masks).

Repeating the Colors -> Map -> Sample Colorize steps outlined in Step Four, apply the chocolate toned step wedge colors to the mid-range tones of your image.

Step Six - Make the highlights "sing"

Select (for this example) the "LLL" layer image (not the mask as you can not Sample Colorize masks).

Repeating the Colors -> Map -> Sample Colorize steps outlined in Step Four, apply the yellow-ish toned step wedge colors to the mid-range tones of your image.

Your image should now be toned using portions of three colorized step wedges and three Luminosity layer masks.

If upon close inspection you find one region or another is too strongly tinted, you can lower the opacity of that layer/mask to something you find more pleasing.  I tend to do this in the shadows/dark tones as my colorized step wedge tends too be too blue to my eye.  So I tend to set the "DDD" layer/mask opacity to 50 percent.

Super Selective tone mapping in the Gimp


In the example screenshot image you can see how I have modified the process just slightly from what is written above.  Note the layer/mask arrangements and visibility settings (the "eye" found just to the left of each layer/mask).

In this example I have set the "LLL" layer/mask above everything else.  This will keep the whites white as I did not tint the "LLL" image.

I moved the "M" layer/mask above the "MMM" layer/mask and tinted both layers.  As you can see, the "M" layer/mask has a grayer mask than "MMM."  This means the "M" layer/mask is more subtle and for it's effects to be seen it has to be placed above the stronger "MMM" layer/mask.

Lastly, the "DD" layer image is cool toned and the opacity of that layer/mask is set to around 50 percent.

This is a lot to take in, but it helps understand why we will do what we do in the next Part Three example where we greatly simplify the entire process.

Tuesday, May 26, 2020

Super Selective Toning in the Gimp - Part One

In a prior blog entry I described a simple means of toning the mid-range of a black and white photograph while keeping the blacks black and the whites white.

Some years ago I remember reading where one of the attractions to using carbon tissue layers in registration to create a black and white photographic print was that a person could vary the colors of each layer.  That is, each carbon tissue layer represents some narrow range of overall image intensity and by carefully selecting the colors of each layer a printer could, for example, use cool tones in the shadows and warm tones in the highlights.

We can achieve the same effect with perhaps even finer tonal controls than carbon prints by using digital black and white images. 

Here is another of perhaps many valid methods for achieving the carbon tissue colorizing controls in digital image processing.

Setup -

Processing -
I will give a very specific set of instructions.  However, keep in mind there are many combinations and variations that might help you express your intentions better.

Before we begin, I want to note that in this example I'm using three strong primary colors so that you can see the blending transition effects from light to dark.  For a proper black and white image we would like never do something like this.

Step One - Create the Base Black and White Image

Open an image in the Gimp.

Mid-Tone color generation and blending using Luminosity Masks


Add a black layer over the base image and set the blend mode of the black layer to "Lch Color".  Flatten the image in preparation for the next steps.

Mid-Tone color generation and blending using Luminosity Masks



Step Two - Create 9 Luminosity Layers and Masks with One Click

Open Filters -> Generic - Luminosity mask setup and watch as new masked layers are generated.  Note how they are arranged with the "Darks" layer set of three grouped layers labled "DDD", "DD", and "D".  Similarly, note how the "Mids" and "Lights" are organized.  We are about to rearrange them.

But before we do, take a close look at how each set of three sub-layer masks are slightly different from one another.  They define how much of a region will be affected when we make changes to the layer image.  Said another way, each mask uniquely describes what portion of the image will be affected by any changes we make to each layer image that each mask is attached to.


Mid-Tone color generation and blending using Luminosity Masks


Step Three - Re-Order Luminosity Mask Layers

When we add color to these Luminosity layers, their arrangement and order will be important.  How the colors will blend and transition between the layers will be determined by the order you choose.  We will now rearrange them to prepare for sample colorizing.

Click on the "Mids" top of group layer (where the "MMM", "MM", "M" sub-layers are organized just below it) and select the up arrow carrot.  When you click on the up arrow carrot after selecting "Mids", the entire "Mids" layer structure will move.  The up arrow carrot is found on a tool bar just below the base image.  Verify that "Mids" collection of three layers and masks are now positioned above the "Darks" collection of three layers.

Mid-Tone color generation and blending using Luminosity Masks

Now click on the "Lights" collection of three layers and masks and again using the up arrow carrot click twice to move "Lights" first above "Darks" and then above "Mids".  "Darks" will now be the first Luminosity layer collection above the base image.  We have simply reversed the order of the layers and their masks.

Mid-Tone color generation and blending using Luminosity Masks


Step Four - Add Highlight Color

Select a foreground color.

Mid-Tone color generation and blending using Luminosity Masks

Deselect visibility (the "eye" found just to the left of the layer image) of the "LL" and "L" layers.

Select the "LLL" layer image (and not the "LLL" mask since we cannot add color to a mask).  In this example we are selecting the layer who's mask most narrowly describes the highlight region of the image.  Selecting "LL" or "L" would broaden the colored highlights further down the tonal range.  This is something to keep in mind as you work with this technique as you can use this to introduce subtle gradations of colors within the tonal region defined by these Luminosity masks.

Select Filters -> Map -> Sample Colorize 

Select Sample: From Reverse Gradient

Select  Get Colors (perhaps not strictly required)

Select Apply

Select Close

Mid-Tone color generation and blending using Luminosity Masks


Here is how the image looks after adding color to the "LLL" highlights layer.  You can begin to see where we are going with all this by looking carefully at the various color wheels in the image we are working on to observe what just changed.

Mid-Tone color generation and blending using Luminosity Masks




Step Five - Add Mid-Tone Color

Select a new foreground color.

Mid-Tone color generation and blending using Luminosity Masks


Deselect visibility (the "eye" found just to the left of the layer image) of the "MM" and "M" layers.

Select the "MMM" layer image (and not the "MMM" mask since we cannot add color to a mask) under the "Mids" layer grouping. 

Select Filters -> Map -> Sample Colorize

Select Sample: From Reverse Gradient

Select  Get Colors (perhaps not strictly required)

Select Apply

Select Close

Here you have a choice and you will need to try both to see which mid-toning works best for you.  In this example I have continued to select Sample: From Reverse Gradient though you could use Sample: From Gradient.

Mid-Tone color generation and blending using Luminosity Masks


This is how the mid-tones are colorized and blended with the "Lights" "LLL" layer that we added in the prior toning step.

Mid-Tone color generation and blending using Luminosity Masks



Step Six - Add Low-Tone Color

Select yet another new foreground color.

Mid-Tone color generation and blending using Luminosity Masks

Deselect visibility (the "eye" found just to the left of the layer image) of the "DD" and "D" layers.

Select the "DDD" layer image (and not the "DDD" mask since we cannot add color to a mask) under the "Darks" layer grouping.

Select Filters -> Map -> Sample Colorize 

Select Sample: From Gradient  (note the change of this field value from the prior two steps)

Select  Get Colors (perhaps not strictly required)

Select Apply

Select Close

Mid-Tone color generation and blending using Luminosity Masks


Here is how the "Darks" look after following this, the final step, in this example.  Carfully observe how the colors transition between colorized regions.  This may have important consequences for the colors you choose in your own work.  There is potentially a lot to consider here.


Mid-Tone color generation and blending using Luminosity Masks




Summary -

As you can see, we have successfully added different colors to the highlight "LLL", mid-region "MMM", and shadows "DDD".  We did this by sample colorizing copies of the base image that are included in each of the 9 layers that were generated by the "Luminosity mask setup".  Each Luminosity layer has a unique mask that defines the region and extent to which the sample colorization will be applied.  In this way we can control the exact colors of, in this example, three different regions - highlights, mid-tones, and shadow.

Remember, we have 9 masked layers to work with.  So we have the possibility to further "finesse" the colors and their transitions.  If/when you choose to take advantage of the 6 masked layers that we did not use in this example, I suggest that you will want to invert the order of "Mids" under the top layer grouping.  That is to say, instead of ordering the "Mids" sub-layers as "MMM", "MM", and "M", reverse this too "M" first, you can leave the "MM" where it is, and move "MMM" to the top. 

The "Lights" and "Darks" sub-layer ordering can be left alone.  As a potentially mind-bending exercise I will leave the reasoning for this to the reader.  On second though, maybe I should cover it here.

If you look at the masks for the "Lights" and "Darks" sub-layers you will see that the most restricted mask is on top, with the following two layers expanding the regions affected by color changes.  So you will want the most restricted color mask on top in the "Mids" so that its color effects will be seen and not hidden _below_ upper more expanded layer mask.

In any event, as you add colorized layers, re-select the visibility "eye" found just to the left of each layer image to make that layer "active" and its effects visible in the overall image.

There you have it.  A potentially mind-bending, mind-exhausting way of subtly controlling colors of different tones across an image.  All this in the pursuit of old carbon tissue photographic image style.

Now, honestly, wasn't that fun?  Well, maybe not.  But at least you have real control over your image, right?








Thursday, May 21, 2020

Selective toning in the Gimp

A friend asked how we might be able to selectively tone an image using the Gimp.  His goal was to make the whites white and the blacks black, but have the mid-tones hold some interesting color.

As with everything digital, there are a gazillion ways of doing things.  For mid-range toning, here is just one way.


Step One - load a color image into the Gimp.  This will be the base layer.

Mid-tone tint steps ~ Gimp


Step Two - convert to Luminosity (human eye tonal intensity matching) black and white.  You can do this by adding a BLACK layer over the base color image and setting the blend mode to "Lch Color" (shown below prior to flatten image) and then flatten the image in preparation for the next step. 

As an aside: I see that by using Luminosity curves in a black and white conversion that I get the kind of tonal separation that I prefer in my black and white images.  In fact this approach, to me, is so good that old silver halide film can not match this.

A simple digital de-saturation (which is what old film used to try and achieve with its "panchromatic" product offerings) makes things muddy.  A filter over RGB curves doesn't give exactly what I wish.  Your mileage will vary, of course.

So once you have a black and white image, however you get there, you can move on to step three.

Mid-tone tint steps ~ Gimp

Step Three - Set the foreground color to something "interesting".  There are a number of colors that emulate things like cold silver, warm tone palladium, sepia toning, etc, etc, etc.  Choose something you like.


Mid-tone tint steps ~ Gimp


Step Four - Add a layer over the base black and white image using the foreground color you just selected

Mid-tone tint steps ~ Gimp

Step Five - Put the new color layer over the base black and white image.  Then select Layer -> Mask -> Add Layer Mask and add a white mask to the color layer.

Mid-tone tint steps ~ Gimp


Step Six -
Select the base image (in this example the color wheel image in the base layer) and select Edit -> Copy Image

Click on the White color layer mask to make it active.  Then select Edit -> Paste.  This will add a copy of the base image as a Mask to the Color Layer.

Now set blend mode of the color layer to either "Lch Color" or "HSL Color" - your choice

Mid-tone tint steps ~ Gimp


Step Seven - Open "Curves" on the Mask image and set the curve as seen below

NOTE: by raising the center of the curve, you _add_ more color to the mid-tones, but only if that's the effect you want.  Play with this to see how your base image toning changes.

NOTE 2: By lowering the ends of the curve you make the whites whiter down the tonal range and the blacks blacker up the tonal range.  For myself, I  don't mind a bit of color in the blacks, so I raise that black end of the curve - to taste, of course

Mid-tone tint steps ~ Gimp

Step Eight - Verify your results.  Flatten your image and save.

Mid-tone tint steps ~ Gimp