Question about colour
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| Question about colour | Chris Moller | 29 Mar 15:28 |
| Question about colour | Rob Antonishen | 29 Mar 15:56 |
| Question about colour | jcupitt@gmail.com | 29 Mar 16:36 |
Question about colour
I did a little experiment last night, creating two rectangles, one of hue = 240, saturation = 90%, and value = 90%, the other differing only in saturation, = 50%, i.e., reducing saturation by 40%. Then, from the Hue/Lightness/Saturation dialogue, I increased the saturation of a selection in the less-saturated rectangle by 40, thinking the colours would then match. They don't. In fact, /no/ adjustment of saturation from that dialogue will make the colours match and, further, adjustment of the saturation also affects the colour value. Adjusting colours that differ only in value (which I assume is the same as what's called "lightness" in the H/L/S dialogue) yields similarly unexpected results: it was possible, using value adjustment alone, to adjust a colour with an HSV triplet of [240 90 50] to [240 90 90], but only by increasing "Lightness" by 61 rather than the expected 40 (or perhaps the at least somewhat intuitive 80, the percentage increase of 90 over 50).
I confess I don't understand colour, but is my understanding even poorer than I thought? Or is this an area in which GIMP needs a bit of work?
(The utterly prosaic background of this question is that my wife runs an eBay business for which I am the reluctant photographer. Frequently, I take multiple pictures of the same object, under the same lighting, differing sometimes only in the distance of the object from the light. The resultant colours in the photographs are frequently significantly different and I use GIMP to try to make them match. This is remarkably difficult to do and if I ever get the time I may undertake to write something for GIMP to make this easier.) (And I won't even comment on the near-impossibility of getting the image colours to perceptually match the in situ colours...)
Question about colour
I confess I don't understand colour, but is my understanding even poorer than I thought? Or is this an area in which GIMP needs a bit of work?
I don't think HSV and HSL are the same colourspace: http://en.wikipedia.org/wiki/HSL_and_HSV
Frequently, I
take multiple pictures of the same object, under the same lighting, differing sometimes only in the distance of the object from the light. The resultant colours in the photographs are frequently significantly different and I use GIMP to try to make them match. This is remarkably difficult to do and if I ever get the time I may undertake to write something for GIMP to make this easier.)
You can try my histogram match script:
http://ffaat.pointclark.net/blog/archives/162-Gimp-Script-Histogram-Match.html
-Rob A>
Gimp-developer mailing list Gimp-developer@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-developer
Question about colour
Hi Chris,
On 29 March 2011 16:28, Chris Moller wrote:
(The utterly prosaic background of this question is that my wife runs an eBay business for which I am the reluctant photographer. Frequently, I take multiple pictures of the same object, under the same lighting, differing sometimes only in the distance of the object from the light. The resultant colours in the photographs are frequently significantly different and I use GIMP to try to make them match. This is remarkably difficult to do and if I ever get the time I may undertake to write something for GIMP to make this easier.) (And I won't even comment on the near-impossibility of getting the image colours to perceptually match the in situ colours...)
I've actually done some work on this. My package (only tangentially related to gimp) includes a colour calibration button, there's a description of the process on the website:
http://www.vips.ecs.soton.ac.uk/index.php?title=Colour_calibration_with_nip2
The idea is that you take a photo including a colour standard (I use the Macbeth). Then select the chart in the photo and click "calibrate" to have it calculate a transform from your camera colour to sRGB. You can then use that transform to colour-correct other images.
Macbeth have a "mini macbeth" now that has the same colour patches, but is a much more reasonable size.
John
