Write a Bitmap Pixel by Pixel in Python?

looked in to System.Drawing import Bitmap, Also I am aware of Pillow but not sure how to install on Rhino Iron Python
basically need to save the image below which is now a list of color values
image

This is hardly the most efficient method, but probably the most simple (using .NET directly and in this case for reading an Excel/CSV file and converting that to a bitmap):

import System.Drawing as sd

if Read:
    
    # Read CSV data file and add to nested list
    csvData = []
    with open(PathRead,'r') as f:
        for line in f.readlines():
            l = line.strip().split(';')
            csvData.append(l)
            
    if Write and csvData:
            
        # Get number of columns and rows in excel data
        columns = len(csvData[0])
        rows = len(csvData)
        
        # Make bitmap
        bm = sd.Bitmap(columns,rows)
        
        # Add pixels
        for i in range(columns):
            for j in range(rows):
                
                # Get data in cell
                cd = csvData[j][i]
                
                # Make color depending on cell data
                if cd in ["a","A"]:
                    col = sd.Color.White
                elif cd in ["y","Y"]:
                    col = sd.Color.Black
                elif cd in ["B"]:
                    col = sd.Color.Yellow
                elif cd in ["W"]:
                    col = sd.Color.Gray
                    
                # Set pixel
                bm.SetPixel(i,j,col)
                
        # Save to file
        bm.Save(PathWrite,sd.Imaging.ImageFormat.Bmp)

160104_CSVToBitmap_00.gh (4.9 KB)

3 Likes

Here is my take just by looping through a list of colors to write, The down side is it takes 30 mins to do 600px image vs C# less than a minute

import System.Drawing 
import math

bmp = System.Drawing.Bitmap(Width,Height)

for x in xrange(Height*Width):
    #index = i + j*Width
    j = int(math.floor(x/Width)) 
    i = int(math.floor(x-(j*Width)))
    col = Color[x]
    bmp.SetPixel(i,j,col)
    bmp.Save(PathWrite,System.Drawing.Imaging.ImageFormat.Bmp)

Wow that’s slow! Can you time the bmp creation part and writing part separately to see where ir’s Taking so long?
You should be able to use

j= x // Width
i= x % Width

To simplify the code
Or even j, i = divmod(x, Width) which does the same

Ahh spotted it - you are saving the bitmap 600 times! No wonder it’s slow :slight_smile:

Got it Thanks!! 900ms

import System.Drawing as sd
import math

bm = sd.Bitmap(Width,Height)

for x in xrange(Height*Width):
    j= x // Width
    i= x % Width
    col = Color[x]
    bm.SetPixel(i,j,col)
bm.Save(PathWrite,sd.Imaging.ImageFormat.Bmp)

Not 600 times but likely more times: widthxheight. For a full HD that is 1920x1080 = 2 073 600 times (:

You’re saving the bitmap to file within the loop, which will be super duper slow. If moving the bitmap save outside of the loop is still too slow, consider using the more advanced lockbits method (as discussed here).

Edit: Looks like you guys already found the culprit. As you were.