Using ColorPerfect to process images in grayscale mode (single channel images)

ColorPerfect is also excellent for processing monochrome images (single channel images) as for example scans of black and white negatives. In fact scanning such images in monochrome mode is what we recommend new users to do. The following will explain some things you should know when working with such images in ColorPerfect.

ColorPerfect has primarily been designed to process three color channel (RGB) images. When we added the capability of processing grayscale images directly to ColorPerfect, we decided to treat all such grayscale images as monochrome RGB images. This design makes no difference for the output as long as the user's color settings are set up to accomodate this but has one advantage. The required color settings are also beneficial for other reasons which we will detail further below.

Choosing the right grayscale profile for ColorPerfect

In order to make sure that ColorPerfect's preview image and the final image put out to Photoshop match in terms of brightness and contrast you need to select a working gray profile that uses the same tone reproduction curve (often a Gamma) as does your default RGB working color space.

If your default color space is sRGB use sGray, if it's Adobe RGB 1998 use Gray Gamma 2.2 and if it's Apple RGB or ColorMatch RGB use Gray Gamma 1.8. Should your default color space be eciRGB v2 please read the lowermost section of this page. Matching the gray profile used and the default RGB working color space in this fashion is the only way to guarantee that the preview image in ColorPerfect will match your final image in Photoshop.

Both the final image and the preview image displayed within ColorPerfect are rendered by Photoshop. The difference between the two is that in order to allow the use of the color manipulating tools as outlined below ColorPerfect always needs to request Photoshop to render the preview as a color image. Naturally there is no additional RGB color profile embedded in grayscale images and because of that Photoshop will always fall back to using its default RGB working color space when requested to render the preview image in color mode. It is not possible for a filter plug-in to get information on what that default color space is so we cannot easily compensate for potential differences.

If you require your output to be in a certain grayscale profile that does not match the tone reproduction curve of your default RGB working color space we recommend processing the image in a matching setup as detailed above and to convert the final image to whatever gray profile you require afterwards but while the image still has a depth of 16 bits.

Availability and purpose of the color manipulating tools when processing grayscale images

ColorPerfect does not hide color manipulating tools like the CC filter system and the Saturation while processing your grayscale images. When using the plug-in on grayscale images directly (Photoshop:> Image > Mode > Grayscale) the only use of these tools is assessing what could be done if you had converted your image to RGB prior to invoking the plug-in. In which case the tools can be used to tone a monochrome image which is in line with traditional chemical means in the wet darkroom. When processing actual grayscale images the preview image alone is in color. ColorPerfect here converts the final image to a true grayscale before being putting it out.

Tools that cannot be meaningfully used use on monochrome images like the FilmType / SubType / FilmGamma calibration system generally are unavailable when processing grayscale images and should also be shunned when processing monochrome images in RGB Mode.

Note on switching between Photoshop:> Image > Mode > Grayscale and RGB

The two Photoshop commands "Image > Mode > Grayscale" and "Image > Mode > RGB" are shortcuts to the "Convert To Profile" command both of which use predefined settings. The predefined settings are that the default RGB working color space and the default gray profile will be used in such conversions. These defaults can be set up as follows: Photoshop: Edit > Color Settings.

If you have a linear scan and switch between RGB and Grayscale modes before invoking ColorPerfect doing so does not change the appearance of your image as long as the default RGB working color space and the default gray profile match as detailed above. If the two don't match in that fashion the linear scan will be treated to have one specific Gamma and will be converted to another tone reproduction curve or Gamma based on that assumption when changing between the modes which effectively alters the image. For grayscale images this can't ruin colors of course but to get consistent results you should be aware of this.

Note for users with eciRGB v2 as their default RGB working color space in Photoshop

We recommend that users only configure Adobe Photoshop to have eciRGB v2 as its default RGB working color space if there is an actually solid reason for doing that in their usual imaging workflow. As soon as that choice is made there is a challenge in producing the equality between the tone reproduction curves of the default RGB working space and default grayscale profile the above article calls for. As far as we know there is no matching grayscale profile with L* as its tone reproduction curve.

Since in principle it is not hard to define such a grayscale profile we did make one for you. We strongly advise however that just as little do we recommend users who do not depend on eciRGB v2 to use our grayscale profile as we recommend using eciRGB v2 as the default RGB working space in combination with ColorPerfect. You may download our LStar grayscale profile here. 16 bit image material created with the LStar grayscale profile can subsequently be easily converted to any other grayscale profile before converting to 8-bit.