Using resmush

resmush is an R package for optimizing local and online image files, individually or in entire directories, with the reSmush.it API. The API is free for personal use and does not require an API key. reSmush.it is also available through WordPress and other tools.

The reSmush.it API provides:

Optimization without an API key.
Support for PNG, JPEG, GIF, BMP and TIFF files.
A file size limit of less than 5 MB.
Compression powered by several algorithms:
- pngquant: Removes unnecessary data from PNG files while preserving full alpha transparency.
- jpegoptim: Lossless optimization based on Huffman table optimization.
- OptiPNG: A PNG optimizer used by several online compression tools.

Examples

Optimize and download an online JPEG image with resmush_url():

library(resmush)

url <- "https://dieghernan.github.io/resmush/img/jpg_example_original.jpg"

resmush_url(url, outfile = "jpg_example_compress.jpg", overwrite = TRUE)

#> ══ resmush summary ═══════════════════════════════════════════════════════════════════════
#> ℹ Input: 1 URL, 178.7 Kb total.
#> ✔ Optimized 1 URL: size is now 45 Kb (was 178.7 Kb). Saved 133.7 Kb (74.82%).
#> Saved result in directory 'C:/user/john_doe/AppData/Local/Temp/'.

Use the qlty argument to adjust the JPEG quality level. For best results, use values above 90.

# Use a low JPEG quality level.
resmush_url(
  url,
  outfile = tempfile(fileext = ".jpg"),
  overwrite = TRUE,
  qlty = 3
)

#> ══ resmush summary ═══════════════════════════════════════════════════════════════════════
#> ℹ Input: 1 URL, 178.7 Kb total.
#> ✔ Optimized 1 URL: size is now 2.2 Kb (was 178.7 Kb). Saved 176.4 Kb (98.74%).
#> Saved result in directory 'C:/user/john_doe/AppData/Local/Temp/'.

JPEG image with visible compression artifacts — Figure 2: Image with visible compression artifacts caused by high compression (`qlty = 3`), compared with Figure 1 (b).

When results are available, all optimization functions invisibly return a data frame with one row per result and columns containing source and destination paths, formatted and raw file sizes, compression ratios and status notes. They return NULL otherwise. Successful API calls also write the optimized files to disk. The following example shows the result for a local image file:

png_file <- system.file("extimg/example.png", package = "resmush")

# Copy to a temporary file for this example.
tmp_png <- tempfile(fileext = ".png")
file.copy(png_file, tmp_png, overwrite = TRUE)
#> [1] TRUE

summary <- resmush_file(tmp_png, overwrite = TRUE)

tibble::as_tibble(summary[, -c(1, 2)])
#>   # A tibble: 1 × 6
#>   src_size dest_size compress_ratio notes src_bytes dest_bytes
#>   <chr>    <chr>     <chr>          <chr>     <dbl>      <dbl>
#> 1 239.9 Kb 70.7 Kb   70.54%         OK       245618      72356

Alternatives

Several other R packages provide image optimization tools:

The xfun package (Xie 2026b) provides:
- xfun::tinify(): Similar to resmush_file() but uses TinyPNG and requires an API key.
- xfun::optipng(): Compresses local files using OptiPNG. The program must be installed locally.
The tinieR package: An R interface to TinyPNG.
The tinyimg package (Xie 2026a): Optimizes local PNG and JPEG files using Rust libraries. It supports lossless PNG optimization via oxipng, optional lossy PNG palette reduction and JPEG re-encoding via mozjpeg.
The optout package: Similar to xfun::optipng() but with more options. It requires additional local software.

Tool	CRAN	Additional software	Online images	API key required	Limits
`xfun::tinify()`	Yes	No	Yes	Yes	500 compressions per month (free tier)
`xfun::optipng()`	Yes	Yes	No	No	None
tinieR	No	No	Yes	Yes	500 compressions per month (free tier)
tinyimg	Yes	Yes (Rust toolchain)	No	No	None
optout	No	Yes	No	No	None
resmush	Yes	No	Yes	No	Personal use only. Files smaller than 5 MB.

Table 1: R packages: comparison of image optimization alternatives.

Tool	PNG	JPEG	GIF	BMP	TIFF	WebP	PDF
`xfun::tinify()`	✅	✅	❌	❌	❌	✅	❌
`xfun::optipng()`	✅	❌	❌	❌	❌	❌	❌
tinieR	✅	✅	❌	❌	❌	✅	❌
tinyimg	✅	✅	❌	❌	❌	❌	❌
optout	✅	✅	❌	❌	❌	❌	✅
resmush	✅	✅	✅	✅	✅	❌	❌

Table 2: R packages: supported formats.

In practice, resmush is designed for quick image optimization with minimal setup, including support for online image files and formats such as GIF, BMP and TIFF. Packages such as tinyimg may be a better fit for fully local workflows focused on PNG and JPEG optimization and fine-grained control over compression settings.

References

Xie, Yihui. 2026a. tinyimg: Optimize and Compress Images. https://doi.org/10.32614/CRAN.package.tinyimg.

Xie, Yihui. 2026b. xfun: Supporting Functions for Packages Maintained by Yihui Xie. https://github.com/yihui/xfun.