Mike Chaney's Tech Corner

When I read RGB colors in CS4 the values shown are different than in QIS "current color". Why is that?
Thank you!

Check the image for the working color space.
It is likely that CS4 opened the image in a different working space than Qimage.
Fred

If image is in given color space let say Pro-photo, how can it be opened in different color space in either application? When I hit CTRL-i it says Pro-photo and CS$ says the same.

Hi Adam,

If you are using a colour picker/sampler type of tool, you need obviously to pick exactly the same spot on the image and ensure it is choosing the same number of pixels. In PS you can adjust the size of the area being selected - it 'averages' the colour over that area.

Best wishes,

Ray

Adam,
I don't have CS to emulate what you are doing.
How are you deciding that the RGB values are not the same?
Is the Prophoto profile embedded in the image? What kind of image, JPG, Tif, ?
I know that CS x  will allow you to open an image in an alternate color space, other than the embedded one.
There are too many variables to venture a guess as to what you might be encountering.

You are welcome to email the image to me.

wathree.ssz@verizon.net

Fred

Excellent point Ray.
What I did in Qimage was use the same image with two different profiles embedded. Then I selected a pixel. ONE, by using the pixel coordinates in Qimage.
I used pixel 833 by 777 in both tests using the same image but one in aRGB and one in sRGB
They come with different readings as expected.
Fred

Hi Fred,

Another point - if using the gretag macbeth (sp) charts from Dry Creek, they have the colour values printed on the patch. Some* of those values are not correct (won't effect going colour to colour, but you may never get the values printed on the chart)

Best wishes,

Ray


(* The first one I checked - 'pro photo' had one wrong value - never bothered after that)

Ray,
This is your 5 cents, but I disagree with you.
Fred,
I'll send you a chart.
Thank you!

I have the answer.
If you shut off the monitor profile, the RGB readings are identical in Qimage as they are on the chart.
Fred

Why is that so? How does QI use monitor profile than?
I don't understand this.

Simply put:
Let's say that my monitor has too much red.
I profile it. The profile creates a table to hold the adjustments needed my my monitor to produce accurate colors.
My profile reduces the red which is stored in the Look Up Table.
Now what I see on the screen is accurate color even though we had to reduce the red to get it to be accurate.
Better now?
Fred

If you open the chart that has an embedded profile, or requires a specific one, and you convert it, the colors may not match.  The color gamut has changed and something MAY HAVE been interpolated.

The Color Options dialog allows control over many colors in the Editor Window (see Using the Text Editor and Using the Hex Editor for more information). Open the Color Options dialog by clicking 'Tools > Options...' and selecting Colors from the list.

Many of the color options have a Foreground color (Fore) and a Background color (Back) that are used when drawing text on the screen. The Foreground color indicates the color of the text, and the background color indicates the color of the background behind the text. Usually darker colors are used for the foreground and lighter colors are used for the background.

Click on a color box to open up the Color Selector Box. Select a color from the box, or click the More Colors... button to open the standard Color Selector Dialog. When using the Color Selector Dialog, select a color from either the color boxes on the left or the color area on the right and click the OK button. Clicking the Add to Custom Colors button adds the current color to the list of 16 colors on the bottom left. The Cancel button will close the dialog without selecting a color. Some colors may be set to None, which means that the foreground or background color will not be modified.