Dear Gimpsters: Since the feature freeze begins in one week I'm taking this opportunity to lobby for what I consider to be a very important addition to the GIMP. The executive summary of the feature is as follows: o The Curves tool should have input and output fields which give the numerical position of the mouse when it is in the graphical part of the tool. o There should also be three fields which give the RGB value of the pixel that the mouse is over when it is in the image window. The Curves tool is the most powerful color correcting tool in Photoshop (as it is in the GIMP). For example there is a very good book by Dan Margulis called "Professional Photoshop" and practically half the book is on how to used Curves to get top notch color correction results. In a nutshell it is amazing what can be done with a numerical approach to color correction. The problem with the GIMP Curves Tool is that the required numbers are difficult to come by. The rest of this request gets into some of the details of how the "color correction by the numbers" technique works and proposes some simple features for the Curves tool that would allow it to do color correction by the numbers. Thus, if you have no interest in this subject there is no need to read any further ;-) ------------------------------------------------------------------------- Now for the more involved justification for the request: The main technique for color correcting with Curves is as follows: o Measure highlight, shadow, and neutral pixel values in the image (i.e., look at the RGB values). Neutral values are grays such as pavement, care tires, etc., Highlights should be white and shadows black. o If grays do not have balanced color, that is R = G = B, then it is likely that a color cast exists that needs to be fixed. o Typically, it is one of the R, G, or B values which is quite different from the other two if a color cast exists. Thus, the correction technique is to move the point of the R, G, or B curve which is incorrect to a better value. For example, suppose I measure a pixel value which should be gray but from the color picker I see that its value is actually R=178, G=203, and B=205. I can see that a little red is missing, that is, the pixel doesn't look quite gray...it has a cyan tinge to it. o To fix the problem in the Curves tool, the value 178 on the red curve is moved up to about 204. Not only does this fix the problem at the pixel in question it also pretty much improves the overall look of the entire image! This is because the image had a cyan color cast that needed to be corrected. Only the pixel that should have been gray was used to make the correction. Now there are two main pains with the GIMP in making use of the above technique. First, in the Curves tool I have to estimate the place where I am on a curve and if I move that point I have to estimate where I've moved it to. Second, the color picker does not stay open at the same time as the Curves tool. Thus, it would be terrific if: 1) Each curve had in input and output box which show the x-y position of the mouse when it was in a curves box. In this way a point on a curve could be very precisely moved to a correcting value. 2) It would be very useful to be able to see the actual numbers associated with R, G, and B when the mouse was in the image window. In that way it would be possible to get all sorts of numeric feadback on highlights, grays, and shadows and it would no longer be necessary to rely on the color picker tool to get the required information. Then in conjunction with the mouse-Shift click option which adds point to curves when pixels are clicked in the image window it would be easy to identify input points to be moved. What do you think? Would this be easy to implement? It would certainly be an important addition to the GIMP since it would add a really professional color correcting feature that is kind of missing. Best Regards, Carey Bunks ------------------------------------ Dr. Carey Bunks Senior Scientist BBN Technologies 70 Fawcett St, 15/2A Cambridge, MA 02138 tel: 617-873-3028 fax: 617-873-2918 email: cbunks@xxxxxxx ------------------------------------
