Legacy ImageMagick Discussions Archive

Hello,
I need to differentiate between the back- and foreground of images to get the most common colors of the centered foreground
neglecting colors at the outer regions if the image.
For this, I need the histogram of each tile in an image. I'm tiling the image in 5x5 subimages and generating the histograms.
Its easy to do in two convert commands.

convert -map netscape: input_image.jpg +gravity -crop 20%x20% input_image_%d.jpg
convert input_image_?.jpg -format "<file>%f</file>\n<histogram>%c</histogram>" histogram:info:-

This generates me a structures output that like

<file>input_image_1.jpg</file>
<histogram>
561: (102, 0, 51) #660033 rgb(102,0,51)
1: (102, 0,102) #660066 rgb(102,0,102)
...
</histogram>
...

Now I want to do the same in one run to avoid the tile files and because I need to spawn processes, and this is quite costy.
I tried:
convert -map netscape: input_image.jpg -crop 21%x21% -format "<tile>%c</tile>" histogram:info:-

Now I'm loosing the information about, which tile which histogram but just rely, that histograms are in the same order as they use to be with the
2 convert method.
is there a way to number or enumerate the histograms appropriately?
Or is there another way to do so?
thanks
nicslos

This seems to work by itself to identify the page, but the page number is always 1 when you add in the histogram: before info:


convert zelda3.png +gravity -crop 50%x50% -format "<file>%t_%p.%e</file>\n<histogram>%c</histogram>" info:

<file>zelda3_1.png</file>
<histogram></histogram>
<file>zelda3_2.png</file>
<histogram></histogram>
<file>zelda3_3.png</file>
<histogram></histogram>
<file>zelda3_4.png</file>
<histogram></histogram>


Perhaps Anthony can supply a solution.

The %c is to print the image comment.
You see no result as the 'zelda' image contains no comment meta-data!

A histogram: generated image contains a comment that lists the histogram as plain text.
Unfortunately it is purly a output image coder. Which means you have to -write the image somewhere to generate any histogram (and its comment). However you can write the image to a mpr: memory register instead of disk, then read the image (and its comment) from that register.

See Histogram
http://www.imagemagick.org/Usage/files/#histogram
And specifically the "mpr:" coder in the very next section... NOTE the histogram comment can be HUGE and time consuming to generate. The previous example generated 3021 lines! This is why a special 'define' can be set to turn off its generation.

Eventually I would like to see a -histogram option that generates an image that other options can -graph or generate profiles from in various ways But that these options are for in the future.