ColorPerfect's Alpha feature and the Alpha Select work around for PhotoLine

What we refer to as the "Alpha feature" is one of ColorPerfect's really advanced tools. It can be used to apply the correct colors from one version of an image to the tonal scale of any second version. This essentially sets the user free to use any of the host application's broad range of tools to produce the desired tonal scale while still relying on ColorPerfect to maintain color integrity. The Alpha feature can be used in combination with all of ColorPerfect's modes. It can be used with TouchUp mode but the feature can also be combined with ColorNeg, ColorPos and PerfectRAW directly.

This feature was introduced back with ColorPerfect 1.05 and the idea behind it is to be able to use the advanced facilities of Photoshop and PhotoLine; curves, levels, masked adjustment layers, etc. to produce an image which has the perfect tonal scale (underlying B&W image) but lacks color integrity. Then, convert that image to grayscale using ColorPerfect and let ColorPerfect apply the original colors to the grayscale so that color integrity is restored. Of course, now that this tool is available many more creative uses will flow out of it.

What is the difference between the Alpha feature and Alpha Select

Our original Alpha feature currently exclusively works when the Plug-in is paired with Adobe Photoshop as its host. That is so because the feature relies on using a fourth color channel as the carrier for the desired tonal scale and also on a technique for calling the plug-in that does not work in the other hosts. Such an extra color channel is often referred to as an alpha channel - which gave the feature its name.

For PhotoLine we have added an alternative method that relies on a selection mask as the carrier for the desired tonal scale instead: Alpha Select.

Alpha Select is disabled by default and needs to be enabled for any mode in which you plan to use it. Simply check the "Use Alpha Select" checkbox on ColorNeg, ColorPos and/or TouchUp mode's option screens to show the Alpha Select checkbox on the Start panel whenever a selection is available for an image when calling the plug-in. The actual Alpha feature will allow for a tonal scale with 16 bit precision to be transferred while selection masks only store 8 bit precision. When used to hold the tonal scale of a final image this technical detail makes little difference though.

Using the Alpha feature (Photoshop) or Alpha Select (PhotoLine) on positive images


To illustrate the use of the Alpha and Alpha Select features I chose a RAW photo of a San Francisco street scene. Dropping the original RAW file on our auxiliary program MakeTiff produces a linear Tiff file that can be opened in Photoshop or PhotoLine without any further processing and which can then be processed into a final positive image using ColorPerfect's PerfectRAW. That the Tiff image created by MakeTiff looks as dark and as green as it does is normal and expected as explained in another article.

With PerfectRAW we can quickly create a first positive image from the photo that has the correct color information we are interested in. Saving this version as a copy we can then go on and create the version having the tonal scale we desire.

For that we can use Photoshop's or PhotoLine's broad range of tools without paying too much attention to color. Only pixel moving commands like the clone brush should be left for later. For this example I specifically chose tools that would wreck the color beyond repair but tried to create an interesting high contrast tonal scale in the process.

Once we are done creating the second version of our image we need to use ColorPerfect's TouchUp mode to run Saturation to 0 and to produce a gray image version.

Skip this paragraph if you're using PhotoLine. The Photoshop screen shots used here were taken on my German version of Adobe Photoshop and I hope you'll be fine with that. After creating the gray image version we need to select any one of the gray image's three color channels e. g. the green channel so that only it shows. We then copy this channel (Ctrl+A, Ctrl+C) and insert it as a fourth color channel into our image version holding the original colors. To do this first create a new color channel in that document, activate it alone and then paste (Ctrl+V) the data you copied into it. The image file used for this must only consist of a background type layer (not multiple layers or a layer that allows for transparency) or the final step would be impossible to perform: Selecting all four color channels so that they are visible and active (the eye icons must show in front and the channel names must be highlighted as shown). Once you have this set up and call ColorPerfect the Alpha feature will get invoked automatically.

Skip this paragraph if you're using Photoshop. In PhotoLine we need to save the gray image as a temporary PLD file instead. The use of the PhotoLine image format is required here. After saving the PLD the second image can be closed. Return to the initial image saved before and use PhotoLine's Load Mask command to load the temporary PLD file as a selection mask. The command is located at the Menu: Tool => Mask => Load Mask. With the selection in place we can then call ColorPerfect to apply the original colors to the alternate tonal scale we created. The Alpha Select checkbox should show on the Start panel. If it does not we'll need to activate the "Show Alpha Select" checkbox on the current mode's options screen and use the Revert (<<) button to show the Start panel again after activating the option.

All we really need to do after triggering the actual Alpha feature or checking the Alpha Select checkbox is leaving the plug-in by pressing the OK button.

We could of course also use some of ColorPerfect's tools before doing that. Specifically using Highlight compression and the Saturation adjustment can often be useful. Most of the controls in ColorPerfect will function, but will behave differently than when working with a normal image. This is because we are using the Alpha Channel to completely specify the grayscale image underlying the color image. Thus the controls which affect only the grayscale image (Black, Highlights, Gamma, Zones,...) would be completely ineffective while controls which affect just color (CC, saturation, etc.) would behave normally and controls which affect both color and the grayscale image would have only their color function.

However, we decided that rather than have Black, Highlights, Gamma, and Zones be completely non-functional and useless, we would instead have them operate on the grayscale image given in the Alpha Channel, thus giving the ability to fine tune the underlying grayscale image. For the Alpha feature's 16 bit tonal scale there will be more leeway for doing this than with Alpha Select.

At present we have not altered the rest of the controls and the effects of White and BP in particular can be strange - but useful if you experiment with them. One unexpected use is in eliminating "color noise" which can crop up when using this method, particularly when working "outside the box." These controls can either increase or decrease such noise.

Upon pressing the OK button ColorPerfect creates a version of the image that maintains the tonal scale of our off color adjustment but has the colors from our original image restored to it. In PhotoLine we can now deactivate the selection (Ctrl+D), in Photoshop we can delete the alpha channel. If we feel that we have overdone it with the adjustment it often is a good idea to blend our adjusted and original images to a suitable degree.

Using the Alpha feature (Photoshop) or Alpha Select (PhotoLine) directly on color negatives


The same method can be employed when working with color negatives. As a second example I chose a photo my grandfather took of me as a boy, playing with some toy cars. The linear scan of the original negative can quickly be inverted using ColorPerfect's ColorNeg mode. I did not do anything elaborate in this negative to positive conversion. Choosing one of ColorNeg's built in Kodak film characterizations for a legacy consumer film type produced reasonably good color for this image right away.

As the second image version I made one deliberately ignoring the physics of scene through negative to positive transfer. I used Photoshop's Image => Adjust => Invert command (PhotoLine's Tool => Color => Invert command) which basically just flips an image's brightness in a way that lets black become white and vice versa. This tool creates a pseudo negative from any positive image or returns such a pseudo negative to its original color image. For actual color negative film things do not work this way at all because it's the films densities that are additive and not a given scene's intensities.

Nonetheless I combined this adjustment with some equally far out adjustments using RGB curves. I came up with this alternate version of the image. Its colors are totally beyond repair but using the Alpha feature or Alpha Select as outlined above to apply this second version's tonal scale to the original negative works just fine, does interesting things to my jeans' fabric and lets the little bumper stickers on my toy box stand out more clearly.

Using ColorNeg mode in combination with AlphaSelect yields a very different positive image. Again if we feel that we did too much here it can be a good idea to blend some of the original image version back into the result of the artistic adjustment. Such can be accomplished using layers and layer opacity or using more elaborate methods involving layers, a feathered eraser, the history brush and/or Photoshop's Edit => Fade command. Comparing with the original image again we find that being playful about what to try combining with the Alpha feature can pay off in unexpected ways.

What's new about this? Doesn't the same kind of color transfer simply work using Lab mode in Photoshop?


The short answer to the second part of the question is no. While some things involving the Lab color mode are the next best thing to our work flow in Photoshop and PhotoLine themselves achieving the same quality of result is impossible when using them. If you have never employed Lab mode for something like this please don't read on. The following is not relevant for your work with ColorPerfect and ColorPerfect does not use Lab.

For those interested in this question in more detail I'll still keep the answer brief. The technical difference is that ColorPerfect's Alpha feature works independent of the source color image's brightness. If we had a rather dark original color image - which would be absolutely fine with it being a 16 bit image - and would transfer the target tonal scale we made above into that source image by copying one image's Lab L channel to the other the result would massively lack a certain color quality. The quality that looses precision with increasing differences in brightness here is sometimes referred to as chromaticness. The degree it is off differs at a pixel level and there is no way in Photoshop or PhotoLine to remedy that in a precise way. When using ColorPerfect for the transfer of the new tonal scale to the dark source image's color the result will be identical to the one shown above. It simply does not matter if the original color image is dark or bright.

The issue shown here for adjustments to L* in L*a*b* images is possible to solve mathematically by the way. We did solve it for our legacy Gamsat plug-in which did use L*a*b* internally and we called the correction adjustment GamSat featured for this Ambiance. We believe the Ambiance concept to be original with us, too but ColorPerfect no longer needs it because of our new Complete Color Integrity approach to digital imaging.