Manipulating imagedata - quickest technique?

[David Bovill]

David Burgun wrote:
> I wrote an External Command to do image processing work. It is *way* 
> faster than doing it in TranScript. It also implemented an image cache.
>
> If you want to write an External Command, I can give you some pointers.
That would be very useful David.  For this example - writing an external 
for image contrast and brightness - how long would it take - that is for 
someone who knows how to do it :)


Mark Smith wrote:
> on doLighten imageName
>   
...
>   repeat for each line L in the keys of pixArray
>     put min(pixArray[L] * 1.5,255) into pixArray[L]
>   end repeat
...
> end doLighten

Thanks for the code Mark...

A question about how "lighten" works... I have some functions for HSV to 
RGB conversion (they are a bit old and am sure can be optimized) - using 
HSV sliders on individual colours - I get - but as i don't have 
photoshop installed here - I am not sure how it should work with an image?

If I change a Velocity slider for an image does it:

    a) set all velocity values for each pixel to the new value

    b) multiply each existing pixel velocity value by a percentage 
change and then set

Oh and why should multiplying each rgb value by 1.5 lighten an image?

function colour_RGBtoHSV r, g, b
    -- version original,10/3/03
    if g is empty then
        put item 3 of r into b
        put item 2 of r into g
        put item 1 of r into r
    end if
    colour_ConvertRGBtoHSV r, g, b, h, s, v
    return h,s,v
end colour_RGBtoHSV

function colour_HSVtoRGB h, s, v
    -- version original,10/3/03
    if s is empty then
        put item 3 of h into v
        put item 2 of h into s
        put item 1 of h into h
    end if
    colour_ConvertHSVtoRGB h, s, v, r, g, b
    return r,g,b
end colour_HSVtoRGB

on colour_ConvertRGBtoHSV r, g, b, @h, @s, @v
    set the numberFormat to "0.###############"
   
    put r / 255 into r
    put g / 255 into g
    put b / 255 into b
   
    put max(r,g,b) into maxv
    put min(r,g,b) into minv
    put maxv - minv into diff
   
    if maxv <> 0 and diff <> 0 then
        put diff / maxv into s
       
        put (maxv - r) / diff into rc
        put (maxv - g) / diff into gc
        put (maxv - b) / diff into bc
       
        if r = maxv then put bc - gc into h
        else if g = maxv then put 2 + rc - bc into h
        else if b = maxv then put 4 + gc - rc into h
        multiply h by 60
        if h < 0 then
            add 360 to h
        end if
    else
        put 0 into s
        put 0 into h
    end if
   
    put round(h) into h
    put round(s * 100) into s
    put round(maxv * 100) into v
end colour_ConvertRGBtoHSV

on colour_ConvertHSVtoRGB h, s, v, @r, @g, @b
    set the numberFormat to "0.###############"
   
    divide s by 100
    divide v by 100
    if s is 0 then put v,v,v into rgb
    else
        divide h by 60
        put trunc(h) into i
        put h - i into f
        put v * (1 - s) into p
        put v * (1 - s * f) into q
        put v * (1 - s * (1- f)) into t
       
        if i is 0 then put v,t,p into rgb
        if i is 1 then put q,v,p into rgb
        if i is 2 then put p,v,t into rgb
        if i is 3 then put p,q,v into rgb
        if i is 4 then put t,p,v into rgb
        if i is 5 then put v,p,q into rgb
    end if
   
    put round(item 1 of rgb * 255) into r
    put round(item 2 of rgb * 255) into g
    put round(item 3 of rgb * 255) into b
end colour_ConvertHSVtoRGB