Retired: Bounty #12 - PNG Encoder/Decoder - $14,000

This is the first bounty in a series of bounties we are releasing this week in the run up to Motoko Bootcamp. Winners of the Bootcamp’s Intermediate level will get first crack at selecting one of these bounties to complete.

PNG Encoder/Decoder - #12

Current Status: Discussion

  • Discussion (02/20/2022)
  • Ratification
  • Open for application
  • Assigned
  • In Review
  • Closed

Official Link

Bounty Details

  • Bounty Amount: $5,000 USD of ICP at award date - $5000 USD of ICP Match Available
  • DFINITY Bounty Accelerator Grant Match Available: $5000 USD of ICP at award time - (For every ICP sent to 9c935803b4ee39d89d6b4eaf2ead548df6c1cf7314cc74721d06f5d1a131b37c, will add $125 USD of ICP at award date to the bounty, up to the first 40 ICP donated, After 40 ICP, donations to the above address will add .25 ICP to this issue and .75 ICP to fund other initiatives)
  • Project Type: Single Contributor
  • Opened: 02/20/2021
  • Time Commitment: Weeks
  • Project Type: Library
  • Experience Type: Intermediate - Motoko
  • Issue Type: Motoko Library


This bounty gives the opportunity to

  • learn how png works
  • learn advanced motoko parsing and type management
  • learn about cycle management and multi step processes

The goal of this bounty is to create an encoder/decoder for PNG written in Motoko. PNG is an image format that compresses raw pixels into a manageable file size. PNG is supported by most browsers as an image format for natively displaying pictures.

More info about PNG can be found at:

Example PNG libraries can be found at:

The library will need to support decoding and encoding large images that likely outrun the current cycle limit. You will need to use a library like Using pipelinify is not required if another, better method is available. The bounty applicant may also enhance for their needs.

Some work on this issue can be found at

The library will need to provide the following functions(or equivalent with a different multi-step processing library):

decode_meta(Buffer<Buffer.Buffer<nat8>>) -> PNG // this may need to be a step process if you have to access the whole file to get meta data

decode(Pipelinify.ProcessRequest) -> Pipelinify.ProcessResponse; //sets up a decode process

decode_process(Pipelinify.StepRequest) -> Result<ProcessResponse,ProcessError>; //executes a step

encode(Pipelinify.ProcessRequest) -> Pipelinify.ProcessResponse; //sets up a encode process

encode_process(Pipelinify.StepRequest) -> Result<ProcessResponse,ProcessError>; //executes a step

decode_result(Pipelinify.ProcessingStatusRequest) -> Buffer<Buffer.Buffer<nat8>>, metadata: PNG};

encode_result(Pipelinify.ProcessingStatusRequest) -> Buffer<Buffer.Buffer<nat8>>;

clear_cache(?Pipelinify.ProcessingStatusRequest) -> bool; //clean out any pipelinify cache for a status request, or the entire cache if null

type PNG = {
    //see the PNG spec and define this type

The ProcessRequest variables will need to be defined by the developer to conform with the spec. For this bounty, the dev may implement one optimal configuration of the compression inputs. A future bounty can allow for more customization.

Results should generally be returned in Buffer.Buffer<Buffer.Buffer> so that files can be manipulated in memory. The subchunks should not exceed 2MB so that they can be shipped to other canisters under the file transfer limit. The Candy Libray that Pipelinify uses provides a number of functions to help with these limitations. Feel free to refactor candy and submit improvement pull requests.

The developer will need to experiment with process chunking strategies and make recommendations about how much data can be processed during one process cycle. Hopefully, we can remove this requirement once deterministic time slicing is integrated.

The final delivery should include test cases for both single step and multistep encoding/decoding.

The package should be deployed as a vessel package.

To apply for this bounty you should:

  • Include links to previous work writing tutorials and any other open-source contributions(ie. your github).
  • Include a brief overview of how you will complete the task. This can include things like which dependencies you will use, how you will make it self-contained, the sacrifices you would have to make to achieve that, or how you will make it simple. Anything that can convince us you are taking a thoughtful and expert approach to this design.
  • Give an estimated timeline on completing the task.
  • Post your application text to the Bounty Thread

Selection Process

The developer’s advisors will propose a vote to award the bounty and the Developer Advisors will vote.

Bounty Completion

Please keep your ongoing code in a public repository(fork or branch is ok). Please provide regular (at least weekly) updates. Code commits count as updates if you link to your branch/fork from the bounty thread. We just need to be able to see that you are making progress.

The balance of the bounty will be paid out at completion.

Once you have finished, please alert the dev forum thread that you have completed work and where we can find that work. We will review and award the bounty reward if the terms have been met. If there is any coordination work(like a pull request) or additional documentation needed we will inform you of what is needed before we can award the reward.

Bounty Abandonment and Re-awarding

If you cease work on the bounty for a prolonged(at the Developer Advisory Board’s discretion) or if the quality of work degrades to the point that we think someone else should be working on the bounty we may re-award it. We will be transparent about this and try to work with you to push through and complete the project, but sometimes, it may be necessary to move on or to augment your contribution with another resource which would result in a split bounty.


The bounty was generously funded by the DFINITY Foundation Accelerator. If you would like to turbocharge this bounty you can seed additional donations of ICP to 9c935803b4ee39d89d6b4eaf2ead548df6c1cf7314cc74721d06f5d1a131b37c. ICDevs will match the bounty 5:1 for the first 40 ICP out of the DFINITY grant and then 0.25:1 after that. All donations will be tax deductible for US Citizens and Corporations. If you send a donation and need a donation receipt, please email the hash of your donation transaction, physical address, and name to More information about how you can contribute can be found at our donations page.

General Bounty Process


The draft bounty is posted to the DFINITY developer’s forum for discussion


The developer advisor’s board will propose a bounty be ratified and a vote will take place to ratify the bounty. Until a bounty is ratified by the Dev it hasn’t been officially adopted. Please take this into consideration if you are considering starting early.

Open for application

Developers can submit applications to the Dev Forum post. The council will consider these as they come in and propose a vote to award the bounty to one of the applicants. If you would like to apply anonymously you can send an email to austin at icdevs dot org or sending a PM on the dev forum.


A developer is currently working on this bounty, you are free to contribute, but any splitting of the award will need to be discussed with the currently assigned developer.

In Review

The Dev Council is reviewing the submission


The award has be been given and the bounty is closed.


DFINITY Accelerator Grant: - $5000 USD of ICP at award date

Other Bounties


Ah, this is one of those superhero bounties.

FWIW, this would be really useful.

1 Like

And we have more coming!

1 Like

I am very interested in this project. I specialize in image recognition and deal with images on a regular basis. I think this would be useful.
However, I am new to motoko so I’m not sure how much I can do. I will first clone your uploaded github code and see how it works.

1 Like

Everyone is new to Motoko, i wouldn’t worry about that lol


This would be a great way to learn Motoko and get paid to do it. Worst case you can’t quite finish the bounty but you get us some percent of the way there. If you decide that you don’t want to finish we can always reassign it.

There are very few low-level binary parsing libraries so some of this may require you to start at the base level. It might almost be easier to start with the GZIP library as it likely is a bit easier to complete and this one would use a bunch of the similar methods used in that one.

Did you participate in the BootCamp this past week? If non of the winners want to work on this one you are welcome to give it a shot. Let’s loop back early next week after the BootCamp prices are handed out.


I participate in the BootCamp, but have not yet finished the assignment.
Please let me know if you have new information about this bounty.

Hello, I’ve been interested in this bounty for a while, as I have some related interest in making visual file formats more accessible on the IC… I was also fortunate enough to participate in the Motoko bootcamp, and have been working on making a different kind of minter; as it were, a functional PNG encoder / decoder would be very helpful for the ecosystem and instructive to implement if I can be assigned to do this bounty.

Also, I see tomoyo above had also expressed interest, if you are still interested maybe we can work together because, from what I hear, this is “no simple task”.

Let me know!

1 Like

@tomoyo and @inviscidpixels Would you all like to work on this one together?

I’m still learning motoko and haven’t finished the boot camp yet, so @inviscidpixels can take this bounty.

Sounds good, @inviscidpixels, it is yours.


Great… thank you for the opportunity.

1 Like

are you still down to share this task with someone? I’m doing my masters in imaging related work with matrices, transformations, and stuff, and I’ve coded in motoko. If youre still cool with partnering up, I’d like to help.

oh and if @skilesare is cool with it too. I know he gave you the approval already.

1 Like

Assigned to @Iceypee with @inviscidpixels maybe providing some assistance.

1 Like

Just beginning but I think I’m starting to understand the bigger picture.


Just an update pushed an indexing and alpha separation method. For now, I’m just going to do inside one canister. I’m still trying to wrap my head around that pipelinify thing. Once I figure that out, I’ll make it scale for two.

If you can get this to work, that would be superhuman!

1 Like

I’m happy to give a tutorial on pipelinify as well. I’ve been meaning to document for a while now.

1 Like

That would be awesome to have a tutorial on pipelinfy. I looked at the source; but very little documentation in code. This pipelinfy would be awesome in other large jobs as well.

Just a weekly update, pushed some test functions and added partial index function. please see github for changes