Biorthogonal wavelets have been used with great success in most of the recent transform image coders. By using the new multiwavelets, one can now easily design fully orthogonal linear phase FIR transform schemes. The aim of our work is to assess whether the added orthogonality yields a performance gain compared to traditional biorthogonal transforms. As comparison platform we use the well-known SPIHT codec, which is based on the significance tree quantization (STQ) principle. Without any particular fine-tuning the multiwavelet codec performs within 0.5 dB of SPIHT. A closer inspection shows however that it is hard to improve on this, therefore re-establishing the rule of thumb that strict orthogonality is not a key factor in image transform coding. More details can be obtained on the WEB at http://lcavwww.epfl.ch/~weidmann/mwcoder