Mysql Algorithm for Determining Closest Colour Match

Question

I'm attempting to create a true mosaic application. At the moment I have one mosaic image, ie the one the mosaic is based on and about 4000 images from my iPhoto library that act as the image library. I have already done my research and analysed the mosaic image. I've converted it into 64x64 slices each of 8 pixels. I've calculated the average colour for each slice and assertain the r, g, b and brightness (Luminance (perceived option 1) = (0.299*R + 0.587*G + 0.114*B)) value. I have done the same for each of the image library photos.

The mosaic slices table looks like so.

slice_id, slice_image_id, slice_slice_id, slice_image_column, slice_image_row, slice_colour_hex, slice_rgb_red, slice_rgb_blue, slice_rgb_green, slice_rgb_brightness

The image library table looks like so.

upload_id, upload_file, upload_colour_hex, upload_rgb_red, upload_rgb_green, upload_rgb_blue, upload_rgb_brightness

So basically I'm reading the image slices from the slices table into PHP and then pulling out the appropriate images from the library table based on the colour hexs. My trouble is that I've been on this too long and probably had too many energy drinks so am not concentrating properly, I can't figure out the way to pick out the nearest colour neighbor if the appropriate hex code doesn't exist.

Any ideas on the perfect query?

NB: I know pulling out the slices one by one is not ideal however the mosaic is only rebuilt periodically so a sudden burst in the mysql load doesn't really bother me, however if there us a way to pull the images out all at once that would also be a massive bonus.

Update Brightness Comparisons.

With Brightness

Without Brightness

Answer 1

I think that you may be better off using HSL instead of RGB as color space. Formulas to compute HSL from RGB are available on the internet (and in the linked Wikipedia article), they may give you what you need to compute the best match.

Answer 2

One way to minimize the difference between the colours (in terms of their RGB components) is you would individually minimize the difference in each component. Thus you're looking for the entry with lowest

(targetRed - rowRed)^2 + (targetGreen - rowGreen)^2 + (targetBlue - rowBlue)^2