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  3. TIFF Files Larger Than 2 GB in IronOCR

TIFF Files Larger Than 2 GB in IronOCR

Curtis Chau
Curtis Chau
Updated:

IronOCR loads image input into a single in-memory buffer through its internal AnyBitmap type. That buffer is indexed by a 32-bit integer, so it caps at roughly 2 GB regardless of available system memory. A TIFF file larger than 2 GB exceeds this limit and fails to load.

The failure is quiet rather than loud:

Loaded pages: 0

OcrInput.LoadImage(filePath) creates an AnyBitmap internally and materializes the whole image into one buffer. Because that buffer is indexed by int, it is effectively limited to about 2 GB no matter how much memory the machine has, so a TIFF slightly over that limit cannot be held. LoadImage(filePath) currently returns zero loaded pages instead of throwing a clear exception; this silent failure is a known issue, and a clearer exception is planned. The single-buffer design is an architectural limit, and native per-page TIFF streaming, which would avoid buffering the whole file, is not yet available.

This affects 2026.5.2. The limit is a runtime constraint, not OS-specific, so it applies across platforms on .NET.

Solution

Split the TIFF into sub-2 GB chunks and pass each chunk to IronOCR as a byte array.

1. Add Magick.NET

Bring in Magick.NET so you can split the TIFF before handing it to IronOCR. Pick the variant that matches your project (Q8/Q16, AnyCPU/x64).

dotnet add package Magick.NET-Q16-AnyCPU
dotnet add package Magick.NET-Q16-AnyCPU
SHELL

2. Split by Page Count and Load as Bytes

Open the TIFF as a MagickImageCollection, break it into page-count chunks that each stay under 2 GB, convert each chunk to a byte array, and load it with OcrInput.LoadImage(byte[]) rather than the file path.

var inputPath = "input.tiff";
var pagesPerChunk = 100;
using var allPages = new MagickImageCollection(inputPath);
int chunkNumber = 1;
for (int i = 0; i < allPages.Count; i += pagesPerChunk)
{
    using var chunk = new MagickImageCollection();
    for (int j = i; j < Math.Min(i + pagesPerChunk, allPages.Count); j++)
    {
        chunk.Add(allPages[j].Clone());
    }
    foreach (var image in chunk)
    {
        image.SetCompression(CompressionMethod.LZW);
    }
    var chunkBytes = chunk.ToByteArray();
    using (var ocrInput = new OcrInput())
    {
        ocrInput.LoadImage(chunkBytes);
        var pages = ocrInput.GetPages().ToList();
        Console.WriteLine($"Loaded pages: {pages.Count}");
        var result = new IronTesseract().Read(ocrInput);
        Console.WriteLine("OCR Text Length: " + (result.Text?.Length ?? 0));
    }
    Console.WriteLine($"Chunk {chunkNumber} processed");
    chunkNumber++;
}
var inputPath = "input.tiff";
var pagesPerChunk = 100;
using var allPages = new MagickImageCollection(inputPath);
int chunkNumber = 1;
for (int i = 0; i < allPages.Count; i += pagesPerChunk)
{
    using var chunk = new MagickImageCollection();
    for (int j = i; j < Math.Min(i + pagesPerChunk, allPages.Count); j++)
    {
        chunk.Add(allPages[j].Clone());
    }
    foreach (var image in chunk)
    {
        image.SetCompression(CompressionMethod.LZW);
    }
    var chunkBytes = chunk.ToByteArray();
    using (var ocrInput = new OcrInput())
    {
        ocrInput.LoadImage(chunkBytes);
        var pages = ocrInput.GetPages().ToList();
        Console.WriteLine($"Loaded pages: {pages.Count}");
        var result = new IronTesseract().Read(ocrInput);
        Console.WriteLine("OCR Text Length: " + (result.Text?.Length ?? 0));
    }
    Console.WriteLine($"Chunk {chunkNumber} processed");
    chunkNumber++;
}
Imports System
Imports System.Linq
Imports ImageMagick

Dim inputPath As String = "input.tiff"
Dim pagesPerChunk As Integer = 100
Using allPages As New MagickImageCollection(inputPath)
    Dim chunkNumber As Integer = 1
    For i As Integer = 0 To allPages.Count - 1 Step pagesPerChunk
        Using chunk As New MagickImageCollection()
            For j As Integer = i To Math.Min(i + pagesPerChunk, allPages.Count) - 1
                chunk.Add(allPages(j).Clone())
            Next
            For Each image In chunk
                image.SetCompression(CompressionMethod.LZW)
            Next
            Dim chunkBytes = chunk.ToByteArray()
            Using ocrInput As New OcrInput()
                ocrInput.LoadImage(chunkBytes)
                Dim pages = ocrInput.GetPages().ToList()
                Console.WriteLine($"Loaded pages: {pages.Count}")
                Dim result = New IronTesseract().Read(ocrInput)
                Console.WriteLine("OCR Text Length: " & If(result.Text?.Length, 0))
            End Using
        End Using
        Console.WriteLine($"Chunk {chunkNumber} processed")
        chunkNumber += 1
    Next
End Using
$vbLabelText   $csharpLabel

Each chunk is a fresh MagickImageCollection cloned from the source pages, re-compressed with CompressionMethod.LZW, then serialized with ToByteArray() and passed to OcrInput.LoadImage(byte[]). Keeping the byte payload under 2 GB is what sidesteps the buffer limit.

3. Tune pagesPerChunk

Adjust pagesPerChunk for your data. Lower it if a chunk approaches 2 GB or if memory is tight; raise it for smaller pages to cut down on overhead.

4. Account for Magick.NET in Deployment

Magick.NET ships ImageMagick native binaries. Those add to package size and bring a native dependency footprint, so factor them into your deployment.

Curtis Chau
Curtis Chau
  Chat with engineering team now
Technical Writer

Curtis Chau holds a Bachelor’s degree in Computer Science (Carleton University) and specializes in front-end development with expertise in Node.js, TypeScript, JavaScript, and React. Passionate about crafting intuitive and aesthetically pleasing user interfaces, Curtis enjoys working with modern frameworks and creating well-structured, visually appealing manuals.

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