Problems working with 8bpp and 24bpp images

Cesar · 15th February 2006, 08:28

Oops, it seems I've forgotten to take alpha channel in account. I suppose you can do it youself.

**SkripT** · 15th February 2006, 15:15

Another time thanks a lot Cesar, your suggestions are very helpfully

It's a great idea to calculate a similar color in the table using the distance between two points, I didn't remember that function

. I will try it and I comment the results.

PD: did you forget to calculate the distance using squares in the function 'obtenirIndexColor'?

Qt Code:

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diff = dR * dR + dG * dG + dB * dB;

diff = dR * dR + dG * dG + dB * dB;

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The results of calculating the distance multiplying each term with itself are the same that calculating it as I did with the absolute value, no?

Cesar · 16th February 2006, 07:54

Originally Posted by SkripT

Another time thanks a lot Cesar, your suggestions are very helpfully It's a great idea to calculate a similar color in the table using the distance between two points, I didn't remember that function . I will try it and I comment the results.

You are always welcome

Originally Posted by SkripT

The results of calculating the distance multiplying each term with itself are the same that calculating it as I did with the absolute value, no?

No I didn't. Consider the example:
The point to approximate: P(100, 100, 100).
Two points to choose betwean: A1(75, 125, 100) and A2(100, 51, 100)

Qt Code:

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diffSkript(P, A1) = |100 - 75| + |100 - 125| + |100 - 100| = 25 + 25 = 50
diffSkript(P, A2) = |100 - 100| + |100 - 51| + |100 - 100| = 49
diffCesar(P, A1) = (100 - 75)*(100 - 75) + (100 - 125)*(100 - 125) + (100 - 100)*(100 - 100) = 625 + 625 = 1250
diffCesar(P, A2) = (100 - 100)*(100 - 100) + (100 - 51)*(100 - 51) + (100 - 100)*(100 - 100) = 49*49 = 2401

diffSkript(P, A1) = |100 - 75| + |100 - 125| + |100 - 100| = 25 + 25 = 50
diffSkript(P, A2) = |100 - 100| + |100 - 51| + |100 - 100| = 49
diffCesar(P, A1) = (100 - 75)*(100 - 75) + (100 - 125)*(100 - 125) + (100 - 100)*(100 - 100) = 625 + 625 = 1250
diffCesar(P, A2) = (100 - 100)*(100 - 100) + (100 - 51)*(100 - 51) + (100 - 100)*(100 - 100) = 49*49 = 2401

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As you can see, the results differ. Which one is the best? You choose

**SkripT** · 16th February 2006, 16:36

You' re right Cesar, the results differ!! I will try some colors and see which one is more aproximated.

Cesar · 16th February 2006, 23:08

Go ahead!

And please, post the results, 'cos I'm too curious

**SkripT** · 17th February 2006, 13:07

Hi, Cesar I have tested a little both versions. In many colors they give me the same results. But, in other cases, your version give me results that looks similar to the original color. Here are two examples:

Color to aproximate: r:85, g:0, b:255
Cesar: r:31, g:82, b:138
SkripT: r:79, g:110, b:140

Color to aproximate: r:255, g:85, b:255
Cesar: r:245, g:207, b:178
SkripT: r:255, g:255, b:255

In other cases where they gave me different results, was difficult to say which of one was closer to the original color because is a very subjective fact. Finally I maintain your version because looks more professional calculating the difference with the distance between points

Cheers.