This free online tool generates image histograms for red, green, blue, and greyscale values. Histograms can be generated for multiple images at once in batch.

You can also export the values into a csv file for further analysis in your spreadsheet application.

Note: All processing is done on the client side. That means your images are not transferred to the server.

How This Tool Works

An image histogram displays pixel value distribution within an image.

This tool basically creates 256 bins for each color (red, green, blue) and greyscale (luma) intensity. The number of bins is shown on the horizontal axis.

The tool then loops through every image pixel and counts the occurrence of each intensity. The counts of occurrences in each bin are then displayed on vertical axis.

Counts for each pixel intensity are normalized to range 0 to 255 before they are displayed on the graph.

I used JavaScript in combination with WebAssmebly to create this tool.

How Are Greyscale Values Calculated

I'm using the following formula to convert red, green, and blue values to greyscale

luma = 0.299*red + 0.587*green + 0.114*blue

Useful links

If you want to know how to generate and show image histogram on Android, you can check out my blogpost where I'm giving more technical details about this topic

I also created some other tools related to photography and image processing. If you'd like to automatically stitch multiple overlapping photos, you can check out my tool that I've created for web and for Android
https://play.google.com/store/apps/details?id=eu.sisik.panotool


You are allowed to use the generated histogram graph images and data freely for any commercial or non-commercial purposes, and you also don't need to give attribution (although linking back to my site is always nice ;D).

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Sixo Apps

If you're curios about the technical aspects of Android or you like image & video processing apps, you might find something interesting amongst the apps that I've published on Google Play