How do you balance ImageJ PNG compression quality and file size for storage and sharing?

1 Why PNG compression matters

PNG compression is the process of reducing the size of a PNG file without losing any information or quality. Compression can save you disk space, make your files faster to upload or download, and preserve the original appearance of your images. However, compression can also introduce some trade-offs, such as longer processing time, higher CPU usage, or compatibility issues with some software or platforms. Therefore, you need to balance the benefits and drawbacks of compression depending on your needs and preferences.

2 How ImageJ compresses PNG files

ImageJ compresses PNG files using the zlib library, which implements the Deflate algorithm. Deflate is a combination of two techniques: LZ77 and Huffman coding. LZ77 finds repeated patterns in the data and replaces them with shorter references. Huffman coding assigns variable-length codes to the most frequent symbols in the data and uses them to encode the data. The result is a smaller file that can be decompressed to the original data without any loss.

3 How to adjust PNG compression level in ImageJ

ImageJ allows you to adjust the PNG compression level in the Save As dialog box. The compression level is a number between 0 and 9, where 0 means no compression and 9 means maximum compression. The default level is 6, which is a good compromise between speed and size. You can change the compression level by typing it after the file name, for example, image.png:7. The higher the compression level, the smaller the file size, but the longer the processing time and the higher the CPU usage.

4 How to compare PNG compression quality and file size in ImageJ

ImageJ provides a handy tool to compare PNG compression quality and file size in the Image > Stacks > Tools > Animation Options dialog box. You can use this tool to create an animated GIF from a stack of images with different compression levels. To do this, you need to create a stack of images with the same dimensions and color mode, but with different compression levels. You can use the Duplicate command to copy an image and change its compression level in the Save As dialog box. Then, you can use the Image > Stacks > Tools > Concatenate command to merge the images into a stack. Finally, you can use the Animation Options tool to create an animated GIF from the stack and see how the compression level affects the file size and quality.

5 How to optimize PNG files for web or email in ImageJ

If you want to optimize your PNG files for web or email, you may want to reduce their size further by using some additional methods. One method is to reduce the color depth of your images, which means the number of colors that can be displayed in each pixel. ImageJ supports various color modes, such as 8-bit, 16-bit, 24-bit, or 32-bit. The higher the color depth, the more realistic and detailed the image, but also the larger the file size. You can reduce the color depth of your images by using the Image > Type > command and choosing a lower bit depth. Another method is to crop or resize your images, which means to change their dimensions or resolution. ImageJ allows you to crop or resize your images by using the Image > Crop or Image > Scale commands. The smaller the image dimensions or resolution, the smaller the file size, but also the lower the quality.

6 How to batch compress PNG files in ImageJ

If you have many PNG files that you want to compress with the same settings, you can use the batch mode in ImageJ to save time and effort. The batch mode allows you to apply a macro or a plugin to a folder of images and save the results in another folder. To use the batch mode, you need to write a macro or a plugin that specifies the compression level and any other options you want to apply to your images. You can use the Macro Recorder or the Script Editor to create and edit your macro or plugin. Then, you can use the File > Batch > Process command to select the input and output folders and run your macro or plugin on all the PNG files in the input folder.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?