Our release of the ColorPerfect plug-in for Adobe Photoshop rendered GamSat 1.0 mostly obsolete
GamSat 1.0 is a plug-in for Adobe Photoshop that was used to change the Gamma, saturation and / or hue of an image. Our release of the ColorPerfect plug-in for Adobe Photoshop as the successor of our original ColorNeg and ColorPos plug-ins rendered GamSat mostly obsolete, too. GamSat is still available as an unlimited 30 day trial version and can be permanently activated with any ColorPerfect license key.
Optimizing images in respect of a specific color photographic paper's Gamut with GamSat
Even the most modern color photographic print processes will not match the full gamut of your RGB working space. This is due to the nature of such processes and is not likely to change. To help you in assessing the colors you'll achieve many professional labs will provide you with soft proofing profiles for the photographic media they work with in their respective production environment. A common mistake made by people who encounter this kind of profile for the first time is that they try converting their images into such a profile. This is contrary to what a soft proofing profile is intended for and will effectively do harm to your image.
To illustrate how you can work correctly with such a profile in combination with GamSat let's look at the digital photo of a back lit rose. The photo has been taken late in the afternoon on a summer day. The flower's petals that are being touched by the sun are very saturated. The image shown as a starting point has already been adjusted with ColorPos to achieve the best rendition of the scene. Let's assume we want to have a print of this image made at a digital lab in Germany printing on Fujicolor Crystal Archive DP II Professional Paper. This is not supposed to imply that that is the ultimate paper to print on. Its just an example that can be replaced by the media you like best or that is available to you.
The lab offers a corresponding *.icc profile for download. Before we can start working in Photoshop we have to download it and place it in the system folder for color profiles. On Windows machines this is Windows / System32 / Spool / Drivers / Color and on the Mac this is Library / Colorsync / Profiles.
In Photoshop we can then customize our proof conditions by selecting menu entry View / Proof Setup / Custom. We are then presented with a dialogue box where we select our soft proofing profile for Fujicolor Crystal Archive DP II Professional Paper at the lab we're going to employ. We will select a rendering intent of relative colorimetric and turn black point compensation on to finish setting up our proof conditions. After leaving the dialogue with the Ok button we can apply the soft proof to our image at any time by hitting Ctrl+Y or by selecting the according entry from the menu View / Proof Colors. What is happening is that Photoshop shows us what our image would look like under the given proof conditions. The image data itself is not being changed. This is just a matter of displaying them.
Please note that any of these color proofs will not quite match the final print. Your computer monitor is illuminated while a color print is reflective. In addition the color paper's surface plays a significant role. We might be printing on the pearlescent surface of a professional portrait paper or maybe on a matte or a glossy surface. Each will have its own characteristics that are not being expressed by any means of soft proofing on a computer screen.
In case of our rose we can see that the very saturated areas of the petals would be rendered incorrectly when printed on the chosen paper. They look more towards magenta than towards the red they would be by nature. Unless we compensate for this in an adequate way the rose will not come out as intended on our final print. If we leave the Proof Colors mode enabled we can work directly on the color proof of our image in GamSat while actually applying the changes to our original. Of course along with the benefits this brings along there also is a certain danger of unknowingly changing the original in a way that remains hidden from view. We will want to be sure that we are working on a copy of our original image file when optimizing for individual printing conditions that might be subjected to change at any time. Since we only want to adjust the highly saturated red areas to a state that is more like their natural appearance we'll first set up a selection to use in our compensations. The selection you see here has been created quickly using the Select Color Range dialogue. Afterwards the edge of the selection has been feathered to a suitable degree.
If you were to do this adjustment in Photoshop you would likely try reducing the saturation somewhat in the Hue / Saturation dialogue. We have pointed out the deficits of that method in our report on Hue and Saturation adjustments. Take a look at the color proof of an adjusted version of the image made with this tool. The color proof does look better than the original's. If we turn off proofing and compare what we have produced with Hue / Saturation to the original rose's photo we will notice though that the luminance of the petals has changed significantly and that they have been desaturated in a way that makes them appear cooler in tone than the rest of the rose.
Let's take a look at how we can do better with GamSat. We'll be using the same selection as we did before. We'll turn color proofing back on and start GamSat. We'll be working mostly on the inside of our selection to reach this color proof of the final image as explained hereafter.
In GamSat we will not do the whole amount of adjustment needed to print the petals in a red similar to that of the remainder of the rose by changing saturation. We would have to desaturate the colors too far to retain the most natural look. Instead we will first darken the petals a little using the Gamma adjustment. In the example a value of about 1.2 was used. We will combine this adjustment with GamSat's unique Ambience adjustment at a setting of 100%. If you are not yet familiar with that you might want to read our report on this new feature. What Ambiance does is adjusting each pixel's saturation according to actual luminance changes. The pixels we have darkened slightly using Gamma will therefore become less saturated which is coherent with an actual change in lighting. By itself this is not enough to get the colors to print the way we want them to. We therefore have to reduce the overall saturation of our selection somewhat. Due to the adjustment done with Gamma and Ambiance a setting slightly below 95% is all it takes to complete what we want to achieve. Now we adjust the outside of the selection to best match our adjustment. This way the darker parts of the rose will remain significantly darker. The color proof of the resulting image which we have already shown previous to giving the details on how it was created will look much more natural than either the original image's or the Photoshop adjusted version's color proof did. If we turn proofing off again you will see even more clearly that GamSat's adjustment has stayed close to the original. It can even also be considered beneficial in this view as the petals have gained in detail. The Saturation adjustment done in Photoshop strays much farther from the original. If we had wanted to reduce saturation that much without introducing a color cast we could easily have created a superior version by reducing the overall saturation further in GamSat while omitting the combination of Gamma and Ambiance but that was not our intent.