AccessViolationException when applying adaptive histogram to large images

[nullpainter]

Prerequisites

• I have written a descriptive issue title
• I have verified that I am running the latest version of ImageSharp
• I have verified if the problem exist in both DEBUG and RELEASE mode
• I have searched open and closed issues to ensure it has not already been reported

Description

When applying an adaptive histogram equalisation to a 21,969 x 9802px image, I receive the following:

Unhandled Exception: System.AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
   at SixLabors.ImageSharp.Processing.Processors.Normalization.AdaptiveHistogramEqualizationProcessor`1.CdfTileData.RowIntervalOperation.Invoke(RowInterval& rows)
   at SixLabors.ImageSharp.Advanced.ParallelRowIterator.RowIntervalOperationWrapper`1.Invoke(Int32 i)
   at System.Threading.Tasks.Parallel.<>c__DisplayClass17_0`1.<ForWorker>b__1()
   at System.Threading.Tasks.Task.InnerInvokeWithArg(Task childTask)
   at System.Threading.Tasks.Task.<>c__DisplayClass176_0.<ExecuteSelfReplicating>b__0(Object <p0>)
   at System.Threading.Tasks.Task.Execute()
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot)
   at System.Threading.Tasks.Task.ExecuteEntry(Boolean bPreventDoubleExecution)
   at System.Threading.ThreadPoolWorkQueue.Dispatch()

Steps to Reproduce

This can be easily replicated using the following code, which fails fast:

using var image = new Image<Rgba32>(20000, 10000);
image.Mutate(c => c.HistogramEqualization(new HistogramEqualizationOptions
{
    Method = HistogramEqualizationMethod.AdaptiveTileInterpolation, 
    ClipHistogram = true
}));

I haven't looked at the code at all, but given the speed at which this fails compared with the length of time it takes to equalise a 10,000px square image, I am assuming this crash happens early in the process during memory allocation.

(Apologies for attempting to process gigantic images)

System Configuration

• ImageSharp version: 1.0.2
• Other ImageSharp packages and versions:
• Environment (Operating system, version and so on): Windows 10
• .NET Framework version: .NET Core 5.0

[JimBobSquarePants]

Can you supply the image?

[antonfirsov]

Can you supply the image?

According to the OP I think this is it:

using var image = new Image<Rgba32>(20000, 10000);

I suppose there is an index overflow here:

ImageSharp/src/ImageSharp/Processing/Processors/Normalization/AdaptiveHistogramEqualizationProcessor{TPixel}.cs

Line 636 in 78a584e

Unsafe.Add(ref cdfMinBase, cdfX) = this.processor.CalculateCdf(ref cdfBase, ref histogramBase, histogram.Length - 1);

I think we should limit usages of Unsafe.* to the essentially critical (and well covered) LoadResizeSave stuff (JPEG, Resize, maybe PNG), and remove it from all other processors. Span indexer is fast.

[brianpopow]

I can reproduce the issue. I will change the pixel access to use GetPixelRowSpan there.