Question

Consider this tcl/tk code: it takes PPM-formated RGB data and saves it to a JPG file

image create photo tmpImg -data $Data -width $Width -height $Height -format ppm
tmpImg write $FName -format jpeg
image delete tmpImg

My question is: how can I set the quality of the resulting JPEG picture?
Is there a “-quality” option in Img::jpeg?
I could not find anything in the sparse documentation available….

Thanks a lot.

Answer 1

The documentation is rather sparse, but these options appear to be supported when reading and writing JPEG images: -optimize, -progressive, -quality, and -smooth. The way you pass them when writing an image is more than a bit funky:

# Write with 90% quality
tmpImg write $FName -format {jpeg -quality 90}

Yes, they’re passed inside the -format option. (Hey, I didn’t invent this bizarre hack!)